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Because of the exoskeleton, arthropods must have flexible areas to be able to move. Such regions are called arthrodial membranes and are particularly vulnerable to bacteria and fungi. Here, we analyzed the secretion in the glands underneath it in a Neotropical harvester (Arachnida, Opiliones) and tested whether it has antiseptical properties. We punctured the membrane, collected and diluted the secretion and quantified proteins and peptides in a spectrophotometer. We also fractionated and analyzed the samples in reversed-phase high-performance liquid chromatography (RP-HPLC) and then incubated the treated fractions and determined growth inhibition by measuring absorbance. The secretions resulted in 42 fractions, among which two had activity against the Gram-positive bacteria Micrococcus luteus and against the yeast Candida albicans. The low concentrations at which the secretions were active are relevant from a biotechnological point of view. For the animals, the secretions possibly prevent infections, including when they are attacked in these regions by predators that pick that spot to bite.

The subfamily Gonyleptinae is the second largest in Gonyleptidae, harboring over 100 species. Gonyleptinae is polyphyletic, nestled in the clade K92, and despite its richness, several species of that subfamily have not had their chemicals of the defensive secretions analyzed. Among these are Gonyleptes curticornis (Mello-Leitão, 1940) and G. horridus Kirby, 1819, the latter being particularly important because it is the type species of the genus, which in turn names the subfamily. Gonyleptes horridus is also used in many phylogenetic analyses, be it using morphological or molecular data. The chemical study of the secretions of these two species by GC-MS and NMR 1H showed the presence of 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl)-methylbutanone, 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl) isobutanone and 4- methyl-1-hepten-3-one in both species. On the other hand, 4-methyl-1 hexen-3-one, benzaldehyde and 3-octanone were observed only in G. curticornis. Both species are Gonyleptinae and chemical mapping of the group corroborates that vinyl ketones are synapomorphy of K92 and that the compound 1-(6-isopropyl-3,4-dihydro-2H-pyran-2-yl) isobutanone is synapomorphic to G. curticornis and G. horridus, but homoplastic to the genus Sodreana Mello-Leitão, 1922. 1-(6-(1-methyl-propyl)3,4-dihydro-2H-pyran-2yl)2-methylbutanone and 4-methyl-1-hepten3-one is also synapomorphic to G. curticornis and G. horridus, but homoplastic in Moreiranula saprophila.

Assessing information about prey before attacking is crucial for predators. Whip spiders (Arachnida, Amblypygi) are predatory arachnids that prey mainly on arthropods and whose first pair of legs concentrates many sensory structures. Nonetheless, these aspects of amblypygid biology have been mostly studied in a few species of Phrynidae and basic information about predatory behavior and sensory morphology remain scarce for other families. In this study, we described the sensory morphology of the antenniform leg and the predatory behavior of Charinus asturius Pinto-da-Rocha, Machado and Weygoldt, 2002, a representative of the family Charinidae. We report the presence of most sensilla types described in the better studied Phrynidae and highlight novel aspects such as the morphology of the tarsal organ and the reduced number of rod sensilla. Our behavioral results underscore the importance of antenniform legs in the predatory behavior of C. asturius. Finally, we suggest new avenues to advance the knowledge about the importance of antenniform legs for capturing living prey.

Consistent inter-individual differences in behavior have been shown in several animal groups, ranging from vertebrates to invertebrates. One of the most studied personality traits in animals is boldness, which is the tendency to expose to risky situations. Theory proposes that individuals’ state (e.g., body energy) would influence the expression of personality traits. In this study, we tested if boldness levels of the harvestman Mischonyx cuspidatus (measured as duration of death feigning/freezing after simulated predator attack) differ between two different states, namely sated and food deprived. We also tested if the degree of repeatability in boldness is affected by the individual state. We found no differences in the levels of boldness expressed by M. cuspidatus when comparing between different conditions (sated and food deprived) at a population level. However, we found that individuals showed more consistency in boldness when sated relative to a food-deprived condition. Finally, we suggest new avenues for future studies addressing personality in harvestmen.

Scorpionism is a worldwide problem that has already made thousands of victims, and multi-disciplinary approaches for controlling their populations are to be more successful. Hens are often mentioned as tools for controlling scorpions; however, systematic/experimental behavioral studies are not available. Moreover, there is no systematic information on the effect of scorpion venoms on hens. Using the venomous yellow scorpionWe attracted hens with corn powder, offered them scorpions and then recorded the hen-scorpion interaction. To test the effects of the sting we manually removed the scorpion's telson.We found that some hens ate up to six scorpions within minutes. By means of an ethogram and drawings, we showed that they exhibited several aversive behaviors when capturing scorpions. Removal of the scorpion telson stopped the aversive reactions, which was not observed in the control group. Finally, hens did not exhibit atypical behaviors after 1, 7 and 30 days and were all alive after 30 days.This is the first empirical and video recorded study providing evidence that hens are clearly affected by scorpion venom but do not die. Therefore, they may have potential to be used in biological control of these arthropods.

Animals that live by rivers may benefit from being able to cross them, but behavioral adaptations are needed. Additionally, being able to remain submerged is also important if the animal moves under water. Here we asked whether the harvestman Heteromitobates discolor (Opiliones), that lives by rivers, (a) can propel itself across the water surface, (b) moves into the water if disturbed and (c) can survive for long periods when submerged. Heteromitobates discolor exhibited two gaits on water, whereas a strictly terrestrial species was not able to propel itself. When experimentally submitted to simulated predator attack on a rock on the river, H. discolor walked onto the water, while a strictly terrestrial species did not. Finally, it was able to survive for 6 h under water, presumably due to the conspicuous air film that formed around its body, which was also observed in a strictly terrestrial species. Altogether, these observations suggest that the aquatic environment is not a barrier for regular activity and can be used as an extension of the terrestrial environment for H. discolor.

Sexual differences in morphology can evolve by sexual selection and/or natural selection. In some species, only males have morphological structures that are used as weapons. Since some weapons may also be used for defensive purposes, males and females may behave differently towards predators. In some species of harvestmen (Arachnida and Opiliones), males have sharp apophyses (“spines”) on their 4th pair of legs whereas females lack them. Those apophyses are used in male–male fights and in antipredatory behaviors. The harvestmen antipredatory repertory also encompasses passive defenses such as thanatosis (death feigning), retaliation (attack on predators), and chemical defense. Due to the sexual differences on weaponry, we hypothesized that males and females of Mischonyx cuspidatus (Gonyleptidae) rely on different defensive strategies. We experimentally induced males and females to perform 3 defensive behaviors: thanatosis, pinching with legs, and chemical release. We predicted that females would engage more in passive and chemical defenses than males, whereas males would rely more on retaliation than females. As expected, females performed thanatosis more often than males. Likewise, males performed retaliation more often than females. We did not find differences in the rate of chemical defense use between the sexes. This study provides evidence that due to sexual dimorphism, alternative antipredatory behaviors may have been selected in the different sexes in M. cuspidatus.

Animals use external and/or internal cues to navigate and can show flexibility in cue use if one type of cue is unavailable. We studied the homing ability of the harvestmanHeteromitobates discolor(Arachnida, Opiliones) by moving egg-guarding females from their clutches. We tested the importance of vision, proprioception, and olfaction. We predicted that homing would be negatively affected in the absence of these cues, with success being measured by the return of females to their clutches. We restricted proprioception by not allowing females to walk, removed vision by painting the eyes, and removed the odours by removing the clutch and cleaning its surroundings. We found that vision is important for homing, and in the absence of visual cues, proprioception is important. Finally, we found increased homing when eggs were present, and that the time of the day also influenced homing. We highlight vision as a previously overlooked sensory modality in Opiliones.

Most harvestman species are dependent on high humidity levels and amenable temperatures for homeostasis. While they are known to actively choose environments with these conditions, no thermo-/hygroreceptor has yet been identified in harvestmen. Using electron microscopy, we investigated the ultrastructure of two types of hair sensilla of the armored harvestman Heteromitobates discolor (Laniatores, Gonyleptidae): namely the sensillum basiconicum and the hooded sensillum. Both structures occur in small numbers (sensilla basiconica: 28 units; hooded sensilla: 4 units) and are distributed on the distal parts of the legs. On the distalmost tarsomeres I and II, the receptor cells of paired sensilla basiconica and single hooded sensillum occupy a large volume of the inner tissue, and appear tightly associated. The sensillum basiconicum is innervated by 3-4 dendrites and has a longitudinal slit giving the impression of a shaft with two flaps, resembling a beak. The slit probably allows for evaporation of sensillum lymph. The hooded sensillum is innervated by two bundles of three dendrites each, has two pore-like structures on its tip and displays an unusual reticulate cuticle of the shaft. Details of shaft cuticle, the evidence of evaporation of sensillum lymph, and specific innervation patterns support our hypothesis that sensilla basiconica are thermo- and/or hygroreceptors. Even though the definite function of hooded sensilla remains unclear, its putative receptor modalities are assessed by means of specific ultrastructures. Finally, we discuss with regard to functional ultrastructures as to whether the evaporation system of sensilla basiconica fits mechanisms of hygroreception as known from current literature.

Pedipalps in laniatorid harvestmen are usually cylindrical and raptorial, but species in Cosmetidae are exceptional in that adults, but not immature, have pedipalps flattened as a spoon. Th...

Phylogenetic relationships in Opiliones (Arachnida) at the suborder level have greatly stabilized in recent years, largely due to advances in molecular systematics. Nonetheless, identifying morphological characters in the context of well-resolved phylogenies is essential for testing new systematic hypotheses and establishing diagnostic markers. Here, we investigate with SEM a promising character system across Opiliones: the sensilla on the distalmost article of legs I and II. We identified four discrete characters and scored species of nearly all families of Laniatores (28 families, 44 species), three Dyspnoi, two Eupnoi and two Cyphophthalmi. Using a phylogenetic backbone compiled from recent and ongoing phylogenomic studies, we trace the evolution of these sensilla using ancestral state reconstruction. We discover a widespread occurrence of three sensilla (a pair of sensilla basiconica and one hooded sensillum) on the anterior legs of all families of Laniatores studied, and that comparable structures occur in the other suborders of Opiliones. Our analysis shows that this sensory field provides diagnostic information at different levels of phylogenetic relationships. We discuss the implications of the widespread occurrence of these sensilla in Opiliones, which have recently been hypothesized as hygro-/thermoreceptors and their putative homology with tarsal organs in Arachnida.

Prey morphology and size are known to influence a predator’s decision to attack and consume particular prey; however, studies that evaluate both traits simultaneously are uncommon. Here, we first described the trophic niche in the mygalomorph spider Paratropis sp. These spiders have a narrow trophic niche and feed mainly on sympatric species such as larvae of lepidopterans and of beetles such as carabids, passalids and scarabeids. Second, we evaluated the effect of prey taxon and size on acceptance and immobilization duration, and built an ethogram of the predator’s behaviors. For each prey taxa, we offered large (approximately same size than the spider) and small larvae (approximately half of the size of the spider) of the aforementioned prey. We classified carabid beetle larvae as the most dangerous prey because of their sharp mandibles and predatory habits, followed by scarabeid larvae; lepidopteran and passalids larvae were considered to be non-dangerous prey. We did not find a significant effect of prey taxon or size on spiders’ acceptance. Prey size did not affect the time invested on each behavioral category, but prey taxon did. Moreover, although spiders used a similar strategy for capturing prey, they spent more time biting carabid larvae than other prey. Our results suggest that, at least in our study area, prey that are dangerous or the predator’s size do not seem to affect Paratropis sp. acceptance per se, but can cause the predator to change the time budget allocated to each behavior.

Acquiring food requires success in all the distinct phases of foraging, among which are detecting, capturing and handling prey. We have looked at prey detection, capturing and handling in three species of armored harvestmen differing in leg length and pedipalp morphology: Discocyrtus pectinifemur, Heteromitobates discolor and Gryne perlata. We recorded males and females in captivity capturing 0.5- to 0.7-mm-long immature crickets without legs III and provide the first detailed description of prey capture in harvestmen of the suborder Laniatores. We have shown that these three species can detect live prey without touching it but only at close range (

There are records of glands that produce sexual pheromones that are released into the environment or applied directly on sexual partners. Within Opiliones (Arachnida), several harvestmen in the suborder Laniatores have sexually dimorphic glands on legs I and IV, the mode of use of which is recorded only in two species but their function is unknown: while walking, males rub the glands against the substrate or against their body. Here we test an alternative and non-exclusive hypothesis that the glands present on the legs of male Gryne perlata (Cosmetidae) produce contact pheromones used in mating. We predicted that males would touch the females with the gland openings or with other male body parts previously rubbed by these glands. We also predicted that there are chemoreceptors on those parts of the females where males touch them. We analyzed 13 videos of G. perlata mating, a species in which the males have glands on legs I and IV of unknown function. We also analyzed 14 videos of Discocyrtus pectinifemur (Gonyleptidae) mating as a control, a species that lacks these glands. Finally, we looked for chemoreceptors on the legs of female G. perlata using a scanning electron microscope. During copulation, males of both species rubbed the legs of females with their first pair of legs, but not with the regions of these legs where the openings of the glands are. The fourth pair of legs were only used to support the body. Rubbing other body parts of the female by males with their glands was not observed during mating. Setae on the legs of the female did not have tip pores and therefore do not seem to be chemoreceptors. We therefore did not find any evidence that these sexually dimorphic glands in G. perlata release contact pheromones during mating.

Chemoreception is a main sensory modality in harvestmen but there has been no experimental evidence of attraction to conspecifics by olfaction excluding contact chemoreception as an alternative explanation. Here, using a Y-maze olfactometer we tested whether the harvestman Mischonyx cuspidatus (Roewer, 1913) is attracted to volatiles of conspecifics. We found that males were attracted to volatiles of other males, but not females. Females were not attracted to female's volatiles, but were marginally more often attracted to volatiles of males. Our results help understanding mechanisms in mating and social behavior in the order Opiliones.

Sexually dimorphic traits are widespread in animals, and include sex-specific weapons, ornamentation and, although less noticed, glands and associated structures. In arachnids, certain lineages of the order Opiliones exhibit diverse forms of dimorphism in the armature and length of appendages (common in Laniatores), as well as in the presence of sexually dimorphic glands (mostly investigated in Cyphophthalmi), positing harvestmen as promising models to study sexual dimorphism. Whereas the evolution and ecological significance of armature have been the focus of recent attention, sexually dimorphic glands remain understudied in groups other than Cyphophthalmi, despite being widespread in Opiliones. We therefore selected the amphi-Pacific family Zalmoxidae as an ideal taxon to investigate the evolutionary dynamics of this trait. We first describe four new species of Palaeotropical Zalmoxis, including a species with sexually dimorphic glands, and describe the morphology of zalmoxid species with sexually dimorphic glands using scanning electron microscopy. Using a previously assembled six-locus dataset supplemented with new terminals, and applying stochastic character mapping, we infer that sexually dimorphic glands evolved once in the Neotropics and at least four times in the Palaeotropic zalmoxids, revealing the evolutionary lability of this trait.

Sexually dimorphic traits are widespread in animals, and include sex-specific weapons, ornamentation and, although less noticed, glands and associated structures. In arachnids, certain lineages of the order Opiliones exhibit diverse forms of dimorphism in the armature and length of appendages (common in Laniatores), as well as in the presence of sexually dimorphic glands (mostly investigated in Cyphophthalmi), positing harvestmen as promising models to study sexual dimorphism. Whereas the evolution and ecological significance of armature have been the focus of recent attention, sexually dimorphic glands remain understudied in groups other than Cyphophthalmi, despite being widespread in Opiliones. We therefore selected the amphi-Pacific family Zalmoxidae as an ideal taxon to investigate the evolutionary dynamics of this trait. We first describe four new species of Palaeotropical Zalmoxis, including a species with sexually dimorphic glands, and describe the morphology of zalmoxid species with sexually dimorphic glands using scanning electron microscopy. Using a previously assembled six-locus dataset supplemented with new terminals, and applying stochastic character mapping, we infer that sexually dimorphic glands evolved once in the Neotropics and at least four times in the Palaeotropic zalmoxids, revealing the evolutionary lability of this trait.

The study of sensory structures has the potential to provide insights into the natural history and evolution of animals. The sensory structures of arachnids are usually concentrated on the pedipalps (the tritocerebral appendages) or on the distal podomere (tarsus) of the anterior walking legs, the latter being the case for armored harvestmen (Opiliones, Laniatores). Therefore, modifications of the tarsus could have direct impacts on the sensory equipment of these animals. Using scanning electron microscopy, we investigated the sensory equipment in an extreme case of reduction in tarsal articles in the harvestman Sandokan truncatus (Sandokanidae), which bears a single tarsomere in all legs, and the potential consequences of this reduction. Additionally, we review the literature on the natural history of the family Sandokanidae. Tarsomeres of all legs are equipped with gustatory sensilla, mechanoreceptors, and a pore organ, but wall-pored olfactory sensilla are restricted to tarsi I and II. Tarsi II present a higher density of olfactory sensilla and also putative campaniform sensilla (strain detectors), which indicates a special sensory function of this pair of legs. Other podomeres are covered with shelled sensilla, a probable chemoreceptor previously unreported in Opiliones. Overall, S. truncatus has types of sensilla largely comparable to harvestmen with longer and subdivided tarsi. However, S. truncatus also exhibits extra-tarsal sensory fields of sensilla basiconica (putative thermo-/hygroreceptors) in previously undescribed sites, and the unique pore organs. Our results establish a basis for further research investigating the natural history, as well as the evolutionary correlations and mechanistic causes of the tarsal reduction in this enigmatic lineage.

We provide a first scanning electron microscopy examination of the Paleotropical harvestman family Podoctidae (Opiliones: Laniatores), focusing on the distitarsus of the legs of Metibalonius sp. Distitarsi I and II are mostly equipped with olfactory sensilla chaetica with wall pores, while those of legs III and IV have gustatory sensilla chaetica with a tip pore, ventral trichomes with ovate tips (non-sensory) and a type of spatulate seta. Spatulate setae are present in adults of both sexes, with no apparent sexual dimorphism, but they are absent in the nymph. Seven of these setae are inserted on the frontal surface of the last tarsomere of legs III and IV, with the tips oriented ventrally. Each seta has an s-shaped socketed shaft, which terminates distally in a spatula-shaped structure. The distribution of spatulate setae, restricted to legs III and IV (walking legs), the position on the distitarsi, and the typical spatulate shape suggest an adhesive function for these structures. Morphology and position suggest that the socketed spatulate setae of Metibalonius sp. and the previously reported scopular spatulate setae of other harvestmen constitute two distinct types of adhesive structures, highlighting the diversity of adhesive structures in Laniatores. Future investigations about the natural history of this species and internal morphology of spatulate setae are necessary to test further functional hypotheses and to determine their behavioral role.

Preliminary observations suggested that the Neotropical harvestman Jussara sp. (Sclerosomatidae, Eupnoi) had a patchy distribution and a marked seasonality, comparable to species in the Northern hemisphere. This would be an unusual pattern, since conditions of temperature and humidity are very different between tropical and temperate environments. Using a mark-recapture method, we investigated the phenology, habitat use and individual movement of Jussara sp. in a tropical rainforest in southern Brazil. We found a very marked seasonality in the population of adults, with a positive correlation between temperature, humidity and number of adults found. Adults were found only in the wet and warm months and significantly preferred the plant Psycothria suterella (Rubiaceae) as a resting substrate, spending the days motionless on its leaves, often in groups. The same individuals were found for a maximum of three months after their first capture, 30 m from their original site of capture. At night, the ha...

Prey consumption depends on the predator's ability to locate, capture and handle prey. We investigated these three steps in interactions between the delicate-bodied recluse spider Loxosceles gaucho (Araneae) and a heavy-bodied and armoured harvestman, Mischonyx cuspidatus (Opiliones). Although previous research suggested that the hard integument of such harvestmen protects them from being preyed upon by spiders larger than Loxosceles , indirect evidence suggested that Loxosceles spiders can subdue these prey. In the present study, we tested the following three hypotheses with regard to L. gaucho : (1) spiders use chemical cues left by prey to select foraging sites; (2) vibratory cues of prey are essential information in the predatory process; and (3) the spider's web sheet allows adequate handling of prey so vulnerable body regions of the prey can be bitten. To understand how a delicate predator can overcome the defences of a heavy-bodied and well-defended prey, we also quantitatively described the spider's behaviour. To test hypothesis 1, we compared the time spent in areas with harvestmen, crickets and no cues. For hypothesis 2, we compared latency to bite and number of bites in the presence or absence of vibratory information, and for hypothesis 3, we compared latency to detect prey, latency to capture prey and predation success. All three hypotheses were rejected. Loxosceles gaucho seems to be exceptional among spiders by not needing its web, indirect prey chemical cues, or prey's substrate borne vibrations to hunt the tested prey. What enables L. gaucho to prey upon M. cuspidatus is its unique hunting strategy, compared to previously studied spiders: it touches the prey with its tarsi possibly to locate weak parts of the prey's body, such as joints and distal parts of the legs, then it delivers several bites to these vulnerable areas. Our study is the first to document and describe how recluse spiders overcome the defences of an armoured harvestman.

The threat sensitive hypothesis predicts that animals modulate the defensive behaviour with the level of threat. Therefore, responses to predator cues may differ from responses to the actual predator in close range. Also, in high threat situations, prey would be expected to use their most dangerous defences. The recluse spider Loxosceles gaucho (Araneae, Sicariidae) is known to prey upon well defended harvestmen such as the laniatorid Mischonyx cuspidatus (Opiliones, Gonyleptidae), which has been reported to use tanathosis, chemical defences, pinching with sharp apophyses on legs, chelicerae and pedipalps. Because of harvestmen’s dependence on chemical stimuli, we tested if M. cuspidatus would change its locomotory behaviour in the presence of chemicals of the recluse spider (low threat situation: spider vs blank vs chemical control; one at a time). Subsequently, we tested harvestmen behaviour in the presence of the spider in close range, a high-threat situation. Finally, we looked at the survival rate of spiders after being pierced by sharp apophyses that M. cuspidatus have on legs IV. The harvestmen only showed defensive behaviours in the high threat situation. Surprisingly, their mostly known defensive behaviours (chemical defence, tanathosis, pinching with chelicerae and pedipalps) were not seen even in the high threat situation. This is the first evidence that these behaviours are not used against a natural predator that has an almost 80% predation success when attacking harvestmen. Pinching with the sharp legs IV apophyses may perforate but do not kill the spiders. We highlight the importance of the traditional descriptive approach with natural predators to understand the specificities of defensive behaviours against different types of predator.

Food consumption in animals is a complex task with multiple steps. Choosing an adequate foraging site is the very first one, and involves not only the presence of prey and predators but also abiotic conditions. Because spiders are usually cannibalistic, conspecifics fall within these two categories in addition to being competitors. Specifically for ambush and cursorial spiders, the type of substrate is also very relevant because spiders often rely on substrate-borne vibrations to find their prey, and distinct substrates propagate vibrations differently. At this point or after contacting the prey, spiders have to decide whether or not to attempt capture. Such a decision involves profitability, prey defenses, and the physiological state of the spider. To capture prey, ambush and cursorial spiders may rely on web sheets, adhesive setae on the tips of the legs, glue-spitting, and venom directly injected from the fangs of the chelicerae. The actual mode of ingestion also varies among species. For almost every step from picking a foraging place to prey consumption, multiple sensory modalities may be used, such as vision, contact chemoreception, olfaction, detection of substrate-borne vibrations, and air displacement. Adequately choosing where to forage, properly detecting, choosing, capturing, and handling prey may have important fitness implications. In this chapter, we summarize the knowledge on these topics with regard to Neotropical cursorial and ambush spiders, detecting gaps and areas better covered within the topics above. Finally, we attempt to suggest promising model species to investigate these different steps of foraging in these animals.

Several arachnid species use chemicals to detect sexual partners. In harvestmen, there are evidences that chemicals may play a role in intraspecific communication. Using the behavior of Discocyrtus prospicuus (Holmberg 1876), whose males expose the penis to females before they engage in mating posture, we tested if males detect females by contact chemoreception (chemicals left on the substrate) and if males detect females by olfaction. First, we exposed males to three experimental groups, where males had to choose between two substrates: female chemicals/blank control; male chemicals/blank control; female/male chemicals. Then, we gave males access to volatiles of males, females, and control simultaneously. We predicted that males would expose the penis when approaching volatiles and chemicals deposited on the substrate by females. We also tested if males spent more time close to the source of female volatiles and on the substrate with female chemicals and if males tapped the substrate with female chemicals for more time than the others. Finally, we put males and females together to observe if males would expose the penis upon touching the female’s cuticle. Most of our predictions were not supported, though males did tap for more time when exposed to female cues instead of male cues and exposed the penis in 70% of the observations when interacting with the female but only after touching her. Our data does not support olfaction as a way to detect females and corroborate the idea that contact chemicals, either on the substrate or on female’s cuticle, play an important role in the detection and recognition of the opposite sex. This is the first evidence in harvestmen that males may react differently to female/male chemicals.

Most empirical and theoretical papers on prey–predator interactions are for animals with long-range detection, animals that can detect and react to predators long before these touch the prey. Heavy-bodied and chemically defended harvestmen (Arachnida, Opiliones) are an exception to this general pattern and rely on contact to detect arthropod predators. We examined the interactions between the Brazilian wandering spider Ctenus ornatus with harvestmen ( Mischonyx cuspidatus ) or control prey ( Gryllus sp. and M. cuspidatus immature, both with soft integuments). Considering a prey–predator system in which fleeing from or reacting to a predator at a distance is not possible, we predicted both a high survival value of near-range defense mechanisms and that mortality would be higher in the absence of such defense mechanisms. We also expected the predator to behave differently when interacting with harvestmen or with a control prey without such defense mechanisms. Our results from laboratory experiments partially matched our predictions: First of all, histological sections showed that the integument of adult harvestmen is thicker than that of immature harvestmen and that of crickets. Adult harvestmen were less preyed upon than the control prey; the heavy armature increases the survival rate but the secretions from the scent glands do not. The predator did behave differently when attacking harvestmen compared to crickets. Despite the large size difference between predator and harvestmen, the protection provided by the armature allowed some of the harvestmen to survive encounters without pre-contact detection, thus greatly reducing the reliance on long-range detection to survive encounters with predators. Harvestmen call for theoretical and empirical work on prey–predator interactions that take into account the possibility that prey may not detect the predator before contact is established.

Morphological characters are essential for establishing phylogenetic relationships, delimiting higher-level taxa, and testing phylogenetic relationships inferred from molecular sequence data. In cases where relationships between large clades remain unresolved, it becomes imperative to establish which character systems are sound predictors of phylogenetic signal. In the case of Laniatores, the largest suborder of Opiliones, some superfamilial relationships remain unresolved or unsupported, and traditionally employed phenotypic characters are typically of utility only at the family level. Here we investigated a promising set of morphological characters that can be discretized and scored in all Opiliones: cuticular structures of the distal podomeres (metatarsi and tarsi). We intensively sampled members of all known families of Laniatores, and define here three new, discrete appendicular characters toward refinement of Laniatores superfamilial systematics: metatarsal paired slits (MPS; occurring in all Laniatores except Sandokanidae), proximal tarsomeric gland (PTG; in Icaleptidae, Fissiphalliidae, and Zalmoxidae), and tarsal aggregate pores (TAP; found in Gonyleptoidea, Epedanoidea, and Pyramidopidae). We conducted statistical tests on each character to characterize the strength of phylogenetic signal and assess character independence, based on alternative tree topologies of Laniatores. All three characters had high retention indices and bore significantly strong phylogenetic signal. Excepting one pairwise comparison, morphological characters did not evolve in a correlated manner, indicating that appendicular morphology does not constitute a single character system. Our results demonstrate the predictive power and utility of appendicular characters in Opiliones phylogeny, and proffer a promising source of diagnostic synapomorphies for delimiting superfamilies.

The postembryonic development of Opiliones (Arachnida) includes three phases: larval, nymphal (with four to eight instars), and adult (when molts cease). The present study aimed to describe the postembryonic development of Heteromitobates albiscriptus (Mello-Leitao, 1932) (Gonyleptidae) including both a morphometric study and SEM analysis of two structures present in the tarsus of nymphs and adults: the “tarsal aggregate pores” (TAPs) and the “tarsal perforated organ” (TPO). The nymphal phase includes five stages, which can be easily recognized by morphometric values. In contrast to the pectinate tarsal claws found in legs III–IV of adults (the main synapomorphy of the genus Heteromitobates in the subfamily Goniosomatinae), nymphs bear smooth claws. First nymphs lack TAPs and TPOs. TAPs seem to have a precisely defined position in both prolateral and retrolateral faces of the tarsus. The number of pores in TAPs grows from three or four among second nymphs to around 20 among adults, and measure around 2.15 μm in diameter with no clear difference between ages. An additional field of pores on legs III–IV (“ventral tarsal aggregate pores”, vTAPs) was detected only among adults. The plates at the base and the apex of the TPOs differ from the ones in between. The length of the TPO and its number of plates increase with each molt. However, there is no discernible pattern of growth throughout the postembryonic development when taking into account both the average size of the plates (ranging between ∼7–11 μm) and the ratio of TPO length to tarsus length.

Generalist predators have to deal with prey with sometimes very different morphologies and defensive behaviors. Therefore, such predators are expected to express plasticity in their predation strategy. Here we investigated the predatory behavior of the recluse spider Loxosceles rufipes (Araneae, Sicariidae) when attacking prey with different morphologies and defensive mechanisms. We expected L. rufipes to show different prey capture strategies and variable acceptance towards each prey type. Potential prey species were collected directly from the web or in the surroundings of the web-building site of L. rufipes. We collected and used the following in our experiments: termite workers (Nasutitermes sp.), lepidopteran larvae (Eurema salome), ants (Camponotus sp.) and isopods (Tylidae). We paired these prey with L. rufipes and recorded their behavior in captivity, quantifying acceptance rate, immobilization time and the sequence of behaviors by the predator. The acceptance rate was lower for isopods but not different among other prey. The immobilization time was higher for isopods than for termites and similar for the other pairwise comparisons. The behavioral sequence was similar for all prey except for isopods, which were also bit more often. Our combined results show plasticity in the behavior of L. rufipes and also show it subdues a potentially dangerous prey (ant) and an armored prey (isopod).

Preliminary observations of the harvestman Leiobunum vittatum found that individuals rub their bodies against the substrate, presenting the possibility of chemical marking. To determine whether or not L. vittatum individuals can detect substrate-borne chemical cues, we compared responses of L. vittatum males and females to substrate-borne male and female cues. We found that individuals of L. vittatum do respond to conspecific cues and that their responses are sex-specific. In response to substrate-borne conspecific cues, male L. vittatum spent more time, engaged in more scraping with their sensory legs I, and engaged in pedipalpal tapping more often in the presence versus absence of conspecific cues (male and female equally). Furthermore, in the presence of conspecific cues, males engaged in two behaviors never observed in females—(a) “fast approach” and (b) “jerking”, the latter of which was never observed in the presence of cricket cues. In contrast to males, females did not spend more time on conspecific cues, but did spend more time tapping their pedipalps in the presence of male vs female cues, suggesting an ability to distinguish between them. A final experiment explored the possibility that females could discriminate among males of varying histories of agonistic interactions based upon their chemical cues. We found no support for this hypothesis. Our results demonstrate that L. vitattum do respond to conspecific cues, and introduce the possibility that intraspecific communication may be mediated in part by chemical cues.

Solifugids (Arachnida, Solifugae) have unique evertable adhesive organs on the tips of their pedipalps, named ‘suctorial’ or ‘palpal’ organs. Previous studies have shown that these organs enable solifugids to climb smooth glass-like surfaces and have hypothesized that these structures facilitate prey capture. Here, we use high-speed videography to demonstrate that the suctorial organs of Eremochelis bilobatus are its primary means of capturing insect prey. We also present calculations of the adhesive pressure exerted by these suctorial organs during real prey capture events.

Animals present an enormous variety of behavioural defensive mechanisms, which increase their survival, but often at a cost. Several animal taxa reduce their chances of being detected and/or recognized as prey items by freezing (remaining completely motionless) in the presence of a predator. We studied costs and benefits of freezing in immature Eumesosoma roeweri (Opiliones, Sclerosomatidae). Preliminary observations showed that these individuals often freeze in the presence of the syntopic predatory spider Schizocosa ocreata (Araneae, Lycosidae). We verified that harvestmen paired with predators spent more time freezing than when alone or when paired with a conspecific. Then, we determined that predator chemical cues alone did not elicit freezing behaviour. Next, we examined predator behaviour towards moving/non-moving prey and found that spiders attacked moving prey significantly more, suggesting an advantage of freezing in the presence of a predator. Finally, as measure of the foraging costs of freezing, we found that individuals paired with a predator for 2 h gained significantly less weight than individuals paired with a conspecific or left alone. Taken together, our results suggest that freezing may protect E. roeweri harvestmen from predatory attacks by wolf spiders, but at the cost of reduced food and/or water intake.

1463-6395 10.1111/j.1463-6395.2008.00341.x; Willemart, R. H., Farine, J.-P. and Gnaspini, P. 2008. Sensory biology of Phalangida harvestmen (Arachnida, Opiliones): a review, with new morphological data on 18 species. 2014Acta Zoologica (Stockholm) 90: 2092013227 Phalangida includes three of the four suborders of Opiliones (Arachnida): Eupnoi, Dyspnoi and Laniatores. We review the literature on the sensory structures and capabilities of Phalangida, provide new morphological data for 18 species and discuss the 11 sensory structures that have been described in the group. Based on the published data encompassing both behaviour and morphology, three conclusions are apparent: (1) species of Phalangida appear to have limited abilities to detect stimuli at a distance; (2) close range olfaction probably helps to find foods with strong odours, but (3) they appear to be highly dependent on contact chemoreception to detect live prey, predators and mates. We also highlight the fact that legs I in the three suborders and pedipalps in Dyspnoi and Eupnoi are very important sensory appendages, thus legs II should not be called the 'sensory appendages' of harvestmen. In conclusion, we highlight the fact that the sensory capabilities, diet, prey capturing and handling ability, and foraging behaviour of species of Phalangida seem to be different from those of most other arachnids. Finally, we suggest future directions for studies in the field of the sensory system of the group.

The evolution of sexually dimorphic traits has been the focus of much theoretical work, but empirical approaches to this topic have not been equally prolific. Males of the neotropical family Gonyleptidae usually present a strong fourth pair of legs armed with spines, but their functional significance is unknown. We investigated the putative functions of the leg armature in the harvestman Neosadocus maximus . Being a non-visual species, the spines on male legs can only be perceived by females through physical contact. Thus, we could expect females to touch the armature on the legs of their mates if they were to evaluate it. However, we found no support for this hypothesis. We did show that (1) leg armature is used as a weapon in contests between males and (2) spines and associated sensilla are sexually dimorphic structures involved in “nipping behavior”, during which a winner emerged in most fights. Finally, we demonstrate that five body structures directly involved in male–male fights show positive allometry in males, presenting slopes higher than 1, whereas the same structures show either no or negative allometry in the case of females. In conclusion, leg armature in male harvestmen is clearly used as a device in intrasexual contests.

We studied the ability to detect food by close-range olfaction and contact chemoreception in the harvestman Iporangaia pustulosa Mello-Leitao (Opiliones: Laniatores: Gonyleptidae). We first tested the reaction of individuals towards tasteless (pure agar), aversive (agar with salt), and food-intake stimulating substrates (agar with saccharose). Only the substrate containing saccharose was consumed. Contact (mainly with legs II) was necessary for detection of the agar and, before ingestion, the stimulus was always tapped with legs I. In the second experiment, we observed the behavior of individuals in an arena with a screened plastic box containing pieces of Tenebrio molitor L. (Coleoptera: Tenebrionidae) larvae. Individuals spent more time on the box containing food than on the control. In the third experiment, in an arena identical to that used in Experiment 2, we introduced a live but motionless T. molitor larva in the box. There was no difference between experimental and control treatments. We also observed the behavior of I. pustulosa in an arena containing live isopods. In first capture attempts, isopods were only detected upon contact, mainly with legs I. Our results suggest that (i) I. pustulosa is capable of detecting food only by its chemical properties; (ii) food with weak odor may not be detected by close-range olfaction; and (iii) legs I and II are important for food detection but, before ingestion, legs I are used to examine potential food items.

We studied the sensory structures and tegumental glands of two harvestmen species, Neosadocus sp. and Iporangaia pustulosa. We also provide field data of dietary items and data on the foraging behavior of Neosadocus sp. in captivity. Food include mostly immobile items such as dead insects, fruits and feces; the mobility of foraging animals in starvation was greater than in satiation conditions; no trichobothria was found; metatarsal paired slit sensilla and three other sensilla are described for the first time in harvestmen. We discuss the possible relationship between sensory structures, diet and foraging mobility, comparing with other groups of Arachnida. We also describe five new tegumental glands, one sexually dimorphic in the metatarsus IV of I. pustulosa males and two that are rubbed against the substrate while walking, present in both species. This is the first morphological evidence that harvestmen might leave chemical marks on the substrate.

The lack of data on the natural history often hampers phylogenetic studies on the evolution of behavior. Herein we provide quantitative field data on foraging and oviposition sites of a Neotropical harvestman belonging to a subfamily with a published phylogeny, Goniosomatinae. Heteromitobates discolor rests during the day on granitic boulders on rivers, laying eggs in sheltered and darker areas. The female guard the eggs and aggressively respond to approaching conspecific females. In the absence of the female, ants, conspecifics and reduviids may predate the eggs. Egg-guarding females are known not to leave the clutch, but males and non-guarding females may leave the granitic boulders and forage on the vegetation at night, close to the river margins and with no difference in the sites explored between males and females. The general features described in H. discolor are similar to what has been reported for other species in this subfamily, suggesting an evolutionary conservatism within the group.

Males of Iporangaia pustulosa (Arachnida: Opiliones) have a sexually dimorphic metatarsus IV, which is thicker and with more glandular pores in males. Here we tested the hypothesis that this glandular area is used by males to leave chemicals in the environment, predicting that the animals would rub the metatarsus IV against the substrate. We have made recordings both in the field and in the laboratory, in several distinct contexts during the day and at night, comprising 67 hours of observations. We also experimentally tested the reaction of both sexes to a filter paper rubbed on the metatarsus gland, with adequate controls. We report and describe for the first time that the metatarsal gland of I. pustulosa is used to leave chemicals on the substrate by rubbing or touching it against the substrate. We also provide evidence that males can control the release of secretions of the metatarsal gland IV.

Field observations suggested that the spider Enoploctenus cyclothorax (Bertkau 1880) avoids preying on the harvestman Mischonyx cuspidatus (Roewer 1913). The objectives of this study were to test the degree to which this prey avoidance occurred, and to test the effects of starvation on predation rates. Laboratory prey-predator encounters showed that 77.8% of the spiders rejected the harvestmen even after severe starvation, dying after sharing the same terrarium with a harvestman for 68.6 ± 21.8 days. Two spiders fed on the harvestmen, but only after one week. In comparison, crickets given to the control group were all consumed after 13 hours. Prey recognition and subsequent avoidance, without conspicuous exudation of the scent glands (92.9% of the cases), occurred only after the harvestman was touched. We conclude that adult E. cyclothorax do avoid preying on M. cuspidatus, even after severe starvation, suggesting that the latter is recognized by the former by its chemical properties.

In various animal species, male sexual dimorphic characters may be used during intrasexual contests as ornaments to attract females, or to hold them before, during, or after copulation. In the well-known harvestman, Phalangium opilio L., 1758, the behavioral functions of these male sexually dimorphic structures have never been studied in detail. Therefore, in addition to a morphometric study, 21 male contests and 43 sexual interactions were analyzed. Our observations revealed that during contests, the male cheliceral horns form a surface by which the contestants use to push each other face-to-face while rapidly tapping their long pedipalps against the pedipalps of the opponent, occasionally twisting the opponent's pedipalp. Scanning electron micrographs revealed contact mechanoreceptors on the pedipalp that would detect the intensity–frequency of contact with the contender's pedipalp. Larger males won almost all contests, whereas the loser rapidly fled. During sexual interactions, the longer pedipalps of the male held legs IV of the female, whereas males with shorter pedipalps held the female by legs III. No contact with the male pedipalps and chelicerae by the females was visible before, during, or after copulation. Soon after copulating, males typically bent over the female, positioning their cheliceral horns against the females's dorsum. Consequently, our data show that the cheliceral horns and the longer pedipalps of the male seem to play an important role, during both intersexual and intrasexual encountering. Resume : Chez de nombreuses especes animales, les ornementations sexuellement dimorphiques des mâles peuvent etre utilisees lors des combats rituels entre mâles ou comme signal afin d'attirer les femelles ou les retenir avant, pendant et apres l'accouplement. Chez l'opilion Phalangium opilio L., 1758, le role precis joue par ces structures n'a jamais ete mis en evidence. Au cours de ce travail, outre une etude morphometrique, nous avons analyse, grâce a des enregistrements video, 21 combats entre mâles et 43 accouplements. Nous avons pu montrer que, lors des combats, les mâles utilisent les cornes portees par les cheliceres pour se repousser lorsqu'ils sont face-a-face, tout en se tapant mutuellement a l'aide de leurs longs pedipalpes, voire en les enroulant avec ceux de l'adversaire. Des micrographies realisees au microscope electronique a balayage revelent l'existence de mecanorecepteurs sur les pedipalpes qui pourraient permettre au mâle de detecter la frequence et l'intensite des contacts des pedipalpes de son adversaire. Les mâles les plus grands gagnent presque tous les combats, le perdant fuyant rapidement. Au cours du comportement sexuel, les mâles a grands pedipalpes les utilisent pour agripper les pattes IV de la femelle, alors que les mâles a pedipalpes plus courts les retiennent par les pattes III. Il n'y a aucun contact tactile de la part des femelles avec les pedipalpes et les cheliceres des mâles avant, pendant et apres l'accouplement. Juste apres l'accouplement, le mâle s'appuie sur le dos de la femelle a l'aide des cornes de ses cheliceres. D'apres nos observations, il semble donc que les cheliceres et les longs pedipalpes des mâles jouent un role non negligeable lors des interactions intra- et inter-sexuelles chez cette espece.

Sexual coercion in the form of forced copulation has been used as a typical example to illustrate the conflict of interests between females and males. Among arthropods, forced copulation has been reported for some groups of insects and crustaceans, but not for arachnids. In the present work, we analyse and describe the behavioral patterns of mating behavior of the climbing camel-spider, Oltacola chacoensis, relating it to relevant morphological features, In this species, the male forcefully clasps the female’s genital region with his chelicerae and locks her fourth pair of legs with his pedipalps. In some cases, the cuticle of the female’s abdomen was damaged by this cheliceral clasping. In contrast to other camel-spiders, the female O. chacoensis never remained motionless during mating, but continuously shook her body, opening her chelicerae notably towards the male. Despite this coercive context, males performed copulatory courtship (tapping with pedipalps) and females showed an apparent cooperative behavior (they remained still during a short period of the sperm transfer phase). These results strengthen the idea that sexual coercion (in the form of forced copulation) and luring behavior (in the form of copulatory courtship) are not two mutually-exclusive male’s strategies during a single copulation.

Associative learning has been demonstrated in many species of invertebrates, but has not been studied in arachnids, except for some spiders and a whip-spider. Herein, we tested the ability of a Neotropical harvestman, Discocyrtus invalidus (Arachnida, Opiliones) to associate a shelter with a chemical stimulus. We used an arena with a white light at the top and two openings on the floor, one giving access to a dark shelter and the other one closed with a mesh. Filter paper with different chemicals (mate or green tea) surrounded both openings. A harvestman (n=37) was released in the arena and its behavior recorded. The procedure was repeated for 14 consecutive days with each individual. We found that harvestmen got faster at finding the refuge, became less exploratory and tended to move toward the open shelter as the days passed. We conclude that the animals learned to associate the chemical stimulus with the shelter.

The wandering spiders Ctenus amphora Mello-Leitao 1930 and Ctenus crulsi Mello-Leitao 1930 are sympatric in central Amazonian rainforests; however, the former is more abundant in sandy soils and the latter in clay soils. In previous studies authors suggested that C. crulsi is competitively superior on clay soils and avoids sandy soils. Thus, we hypothesized that these species differ in their responses to the soil type. To test this, we placed 37 C. amphora and 30 C. crulsi in chambers providing two choices (sand or clay) and compared the proportion of observations in each to evaluate both species' preferences. Ctenus crulsi significantly preferred clay to sand (P < 0.01), while C. amphora showed no evidence of preference between two types of soil. We discuss the possible ecological consequences of this difference in behavior. This is the first study that experimentally shows a difference between the responses of spider species to soil type as an explanation of their coexistence.

Summary We present field data on seasonality, mating behaviour, sites of oviposition, characteristics of egg batches, and parental care of a cavernicolous population of the Brazilian harvestman Goniosoma albiscriptum. We also tested if guarding females became more aggressive than non-guarding ones by allowing a potential predator to approach G. albiscriptum females. Field work was conducted in several visits to a cave, from September 1999 to April 2001. Reproductive activity was detected almost the whole year, with a minor peak in the spring (October-November) and a major peak in the summer (February-March). Average sex ratio throughout the year was female biased. Proportionally, guarding females were found significantly more often in exposed places than females without eggs. No significant difference was detected between the number of eggs laid in exposed and non-exposed places. The mean number of eggs per batch was 69.58±26.96, and the average minimum time of embryonic development was 33.26±9.78 days. T...

Abstract This study provides information on population dynamics and behaviour (gregariousness and defensive tactics) of the Brazilian cave harvestman Goniosoma albiscriptum (Goniosomatinae). Through a mark-recapture study, we observed that this species regularly uses the cave during the day, leaving it to forage on the vegetation after dusk (i. e., a trogloxene species). There were nine groups within the cave, composed of females and males, the latter being the only sex that moved from one group to another (although rarely). Distinct groups used distinct openings of the cave to leave the shelter after dusk. Goniosoma albiscriptum showed a variety of mechanical defensive behaviours, and also exuded scent gland secretions. During dryer and colder months (between April and August), adult and subadult harvestmen aggregated on the cave walls. The individuals that composed the aggregations were not always the same ones. Reproductive activity (detected by the presence of egg batches) was negatively correlated with formation of aggregations. We suggest that intolerance towards conspecifics during the reproductive period may inhibit the formation of aggregations.

To allow an animal to behave appropriately, the location of sensorial structures is expected to be related to their function. As the different leg pairs of arachnids may have different functions (probing x supporting the body), one could expect them to have a different density of sensilla. Moreover, different regions of the same leg (dorsal, lateral, and ventral) would also be expected to have different densities of sensilla, according to the use of each region (e.g., the ventral part is often in contact with the substrate while the dorsal part is not). As caverni- colous animals are expected to be more sensitive than their epigean relatives, one could also expect a different density of sensilla when comparing cavernicolous and epigean animals. Using three epigean and three caverni- colous species of harvestmen (Arachnida, Opiliones), this study aimed at describing the morphology of hair sensil- la on the legs and answering three questions: (1) Are there differences in the density of hair sensilla between the dorsal, lateral and ventral regions of each leg pair of the same individual? (2) Are there differences in the density of hair sensilla between the leg pairs of the same individual? (3) Are there differences in the density of hair sensilla when comparing the leg pairs of individuals of cavernicolous and non-cavernicolous species? The tarsi and metatarsi of all right legs of the six studied species were analyzed under a scanning electron microscope. The results (P < 0.05) showed that, in general: the ventral region of the tarsus was denser in sensilla trichodea than the lateral and dorsal regions, particularly on legs I and II; the density of sensilla chaetica did not differ on legs III and IV, but was greater on the dorsal region of legs I and II; the ventral part of legs I had the higher density of sensilla trichodea of the four pairs, whereas the second pair had the lower density; Holcobunus citrinus (Eupnoi) was the species with higher density of sensilla trichodea, on all legs; the cavernicolous species had a lower density of sen- silla than the epigean species. The results are tentatively related to harvestmen behavior.