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The importance of vision-reliant defensive traits (e.g. warning colours) in mimicry studies is well established, but their effectiveness is limited by visibility. In low light conditions, for instance, acoustic or tactile channels may be more effective. The juvenile and adult stages of the nocturnal hunting Palpimanus spiders audibly stridulate when harassed. Given this we hypothesized that the sound produced by Palpimanus has a defensive role against interspecific predators. Palpimanus though are poorly defended especially against something as large as a gecko. Hence we hypothesized that the stridulation is effective because the spider mimics co-occurring mutillid wasps. We staged predator feeding experiments in which mutillid wasps, sham-operated Palpimanus, silenced Palpimanus and a nonstridulating spider were offered to Eusparassus spiders and geckoes. Stridulating spiders had significantly greater survival against both predators than the nonstridulating treatments and comparable survival to the mutillid wasps. This result represents the first confirmed case of a spider using stridulation against an interspecific predator. Stridulation deterred Eusparasus spiders, while in geckoes stridulation acted postcapture as they dropped the prey instead of attempting to swallow them. For mutillid wasps this dropping response was typically more rapid than with Palpimanus but attempts to swallow silenced individuals were more frequent than sham-operated individuals, which were more likely to be dropped before any attempt to swallow. Analyses of stridulation characteristics of Palpimanus showed they were similar to acoustic signals of four of the co-occurring mutillid wasps and far more so than distress signals of control insects. Our study overall supports the notion that Palpimanus spiders are Batesian mimics of sympatrically occurring mutillids through the use of an aposematic acoustic signal and not just an example of a startle response.

The observable diversity of antipredator defences across organisms demonstrates predation's impact on trait evolution. The functions of many traits that are presumed to have an antipredator function have never been directly tested. The spiny orb-weaving spider, Micrathena gracilis, for example, stridulates when grasped. While stridulation was first hypothesized to be an antipredator defence nearly 50 years ago, no data exist to support this hypothesis. To explore the form and function of M. gracilis stridulation, we first quantified the behavioural and acoustical properties of sound production. Next, using laboratory assays, we directly tested the effect of stridulation on survival with an avian predator – blue jays, Cyanocitta cristata. Finally, we conducted a large mark–recapture field study in which we compared the natural survival of experimentally manipulated adult female M. gracilis that could not stridulate (silenced) versus could stridulate (control). Stridulatory pulses produced broadband frequency spectra, consistent with acoustic antipredator defences in other taxa. We also observed stridulation by male M. gracilis for the first time. In staged laboratory interactions with captive blue jays, we found no differences in survival between silenced and control M. gracilis. Similarly, in our mark–recapture field study, we found no differences in survival estimates between silenced and control groups, nor an effect of stridulation rate. While M. gracilis stridulation closely resembles antipredator stridulation in other arthropods, our behavioural data do not yet provide solid support for an antipredator function in M. gracilis.

The intertidal isopod Dynoides dentisinus is a sexually dimorphic species; males are much larger than females and have a large, horn-like pleonal process (hereafter referred to as a "horn") and large, posteriorly extended uropods. Here, we investigated the function of these structures with regard to their mating system. Behavioral interactions were observed between a male occupying a small tube (resident) and a newly introduced individual (a female or male visitor). When the visitor was male, the resident repeatedly struck the visitor with his horn; each swing was accompanied by a short sound produced by stridulation. The resident also used his uropods to strike the male visitor and then rejected the visitor. The resident struck the female visitor in a similar fashion but eventually accepted her into the tube; during this process, the resident frequently emitted stridulatory sounds. Our field survey found that the members shared a single shelter (barnacle shell) containing groups composed of several males and females. This suggests that the mating system of this species is polygynandry. The number of females in a single barnacle shell was positively associated with the basal diameter of the barnacle shell. However, the number of females was not associated with the body size, horn size, or uropod size of the largest male in the barnacle shell. These results suggest that male body size, horns, and uropods might have evolved as weapons through male-male competition for large barnacle habitats and more females, but that they have not evolved as ornaments via female choice.

Acoustic signals are an essential part of the multi-modal systems of conspecific communication among insects. The patterns of abiotic factors effects on their communication parameters are of great interest for prognostic purposes in current climatic instability and for practical application in order to manage their populations. The aim of this study was to reveal the dependence of the parameters of acoustic signals produced by bark beetle Polygraphus proximus, an aggressive alien stem pest on the environmental temperature. Male stridulatory signals were recorded in seven temperature settings (5–35 °C), and changes in their temporal parameters were evaluated under laboratory conditions. The obtained results allowed us to reveal the pattern of temperature dependence of signals produced by P. proximus. More than half of the insects were found to actively stridulate at 5 °C. Raising temperature caused an increment in chirp rate that continued to increase up to 30 °C. Further temperature increase led to suppression of signaling in most of the tested males. The obtained results showed a number of patterns of temperature effect on the parameters of acoustic signals which might be universal for representatives of different bark beetles genera with various stridulatory apparatus types.

Anthropogenic noise pollution is known to alter the behaviour of acoustically sensitive animals. Many animals also sense vibrations through solid substrates and use substrate-borne vibrations in conspecific communication. The effects of substrate-borne noise pollution, however, remain largely unknown. Here, we investigate the potential for seismic (soil-borne) noise to alter the reproductive behaviour of the burying beetle Nicrophorus marginatus, a species that breeds below the soil surface on vertebrate carcasses and provides biparental care to offspring. Nicrophorus marginatus beetles produce sound using stridulatory structures on the elytra and abdomen, but no ears have been identified in these beetles, suggesting that stridulation might function to produce substrate-borne signals. We examined the timing of stridulation during reproduction, measured neural responses of beetles to substrate-borne vibrations, and measured beetle reproduction in the presence and absence of seismic noise. We found that parental beetles stridulate throughout carcass preparation and the burial process and confirmed that adult beetles are sensitive to low-frequency seismic vibrations. Variables related to brood size were affected in treatments with seismic noise, with burying beetles producing smaller broods with lower total mass than those in control treatments, providing support for the hypothesis that substrate-borne noise may impose fitness costs for soil-dwelling animals. The precise mechanisms leading to reduced brood size remain unknown but may relate to disruption of seismic communication or inaccurate assessment of resource size. Additional investigations are required to understand the degree to which human-generated seismic noise in natural settings influences other edaphic species, and whether these behavioural impacts lead to shifts in edaphic community structure or function.

Hygrobiidae, or squeak beetles, originated in the Triassic-Jurassic and exhibit a relictual distribution in the Palaearctic, Oriental and Australasian regions. Hygrobiids are well known for their s...

Male field crickets (Orthoptera: Gryllidae) produce acoustic signals by wing stridulation, attracting females for mating. A plectrum on the left forewing’s (or tegmen) anal margin rapidly strikes along a serrated vein (stridulatory file) on the opposite tegmen as they close, producing vibrations ending in a tonal sound. The tooth strike rate of the plectrum across file teeth is equal to the sound frequency produced by the cricket (i.e., ~5k teeth/s for ~5 kHz in field crickets) and is specific to the forewing’s resonant frequency. It is subsequently amplified using specialised wing cells. Anatomically, the forewings appear to mirror each other: a file and plectrum exist on both tegmina; however, most cricket species stridulate using right-over-left wing overlap making the stridulatory mechanism directionally asymmetrical by default, rendering the left tegmen’s file unused. Therefore, we hypothesise structural differences between the functional and unfunctional files. Three-dimensional images were used to accurately measure the stridulatory file structure in Gryllus bimaculatus wings. It was found that the left file shows significantly greater variation in inter-tooth distance than the right file, both over the entire file and especially the first sixty teeth (the functional part). Advantages of this modern method over scanning electron microscopy are discussed.

Signalling via substrate vibration represents one of the most ubiquitous and ancient modes of insect communication. In crickets (Grylloidea) and other taxa of tympanate Ensifera, production and detection of acoustic and vibrational signals are closely linked functionally and evolutionarily. Male stridulation produces both acoustic and vibrational signal components, the joint perception of which improves song recognition and female orientation towards the signaller. In addition to stridulation, vibrational signalling mainly through body tremulation and/or drumming with body parts on the substrate has long been known to be part of crickets' close-range communication, including courtship, mate guarding and aggression. Such signalling is typically exhibited by males, independently or in conjunction with stridulation, and occurs literally in all cricket lineages and species studied. It is further also part of the aggressive behaviour of females, and in a few cricket groups, females respond vibrationally to acoustic and/or vibrational signals from males. The characteristics and function of these signals have remained largely unexplored despite their prevalence. Moreover, the communication potential and also ubiquity of cricket vibrational signals are underappreciated, limiting our understanding of the function and evolution of the cricket signalling systems. By providing a concise review of the existing knowledge of cricket perception of vibrations and vibrational signalling behaviour, we critically comment on these views, discuss the communication value of the emitted signals and give some methodological advice respecting their registration and control. The review aims to increase awareness, understanding and research interest in this ancient and widespread signalling mode in cricket communication.

1. Ecoacoustics is increasingly being used to monitor species populations and to estimate biodiversity in marine ecosystems, but the underwater soundscapes of freshwater environments remain largely unexplored in this respect. Few studies exist concerning the acoustic diversity of ponds, but because aquatic plants and many arthropods such as Coleoptera and Hemiptera are known to produce sound, there is potential to use ecoacoustic techniques to monitor changes in biodiversity and conservation value. 2. This pilot study compares the underwater soundscapes of recently restored open-canopy ponds and unmanaged highly terrestrialized ponds situated in an arable agricultural landscape of North Norfolk, UK, in order to assess the benefits of farmland pond restoration. 3. Daytime sound recordings were made for 10 min in each pond and analysed primarily for arthropod stridulations. In addition, six commonly used acoustic indices were calculated to assess the soundscape biodiversity between the unmanaged and the restored ponds. The stridulations of three diving beetle species (Dytiscidae) were recorded in tank studies to assess the potential for individual species recognition from underwater sound capture. 4. Sound-type richness and abundance, as estimated by visually and aurally identifying arthropod stridulation from spectrograms, were significantly higher in the restored open-canopy ponds compared with the unmanaged terrestrialized ponds. In addition, the acoustic indices 'acoustic complexity' and 'biodiversity index' were significantly higher in restored open-canopy ponds than in unmanaged terrestrialized ponds. 5. The three dytiscid water beetle species recorded in a tank were found to produce distinctive and recognizable sounds, indicating potential to create an audio reference library that could be used for automatic acoustic monitoring of freshwater arthropods. 6. Pond soundscapes are rich in biological information and this study suggests that, with further development, automated passive ecoacoustic monitoring could be an effective non-invasive technique for assessing pond conservation value and pond restoration and management success.

In social insects, situations can arise that threaten an individual or an entire colony. When the call for help goes out, different behavioral responses are elicited by signals emitted from nestmates. In ants, the response can be one of redemptive behavior by the worker receiving it. However, little is known about the evolution of this behavior and in which group of ants it manifests. Therefore, this study investigates whether workers of Odontomachus brunneus Patton can act as rescuers, able to detect and respond to calls for help from nestmates. Laboratory experiments were carried out in which the legs of ants were trapped by tape, simulating capture by a predator. Nearby were nestmates able to receive and respond to a request for help. Two experiments were performed: 1. Calls for help were made at different distances, in order to test the response latency. 2. Evaluation of whether rescuers would respond differently to calls for help from nestmates, non-nestmates of the same species, and ants of another species. Finally, evaluation was made of the behaviors of the rescuers when they responded to requests for help from nestmates and ants of another species. It could be concluded from the results that O. brunneus workers respond to signals emitted by workers who may have been captured by a potential predator, prompting the performance of behaviors related to rescue attempts. The signals involved appear to have an optimal range and are species-specific. When exposed to a capture situation, this species transmits audible signals by stridulation, so it is possible that this type of signal may be involved, in addition to chemical signaling.

Bush-crickets (or katydids) of the genus Mecopoda are relatively large insects well-known for their sounds for centuries. Bioacoustic studies in India and China revealed a surprisingly large diversity of sound patterns. We extend these studies into the tropics of South East Asia using integrative taxonomy, combining song analysis, morphology of sound producing organs and male genitalia as well as chromosomes, to get a better understanding of the phylogeny and evolution of this widespread group. Besides the closely related genus Eumecopoda, the genus Mecopoda contains some isolated species and a large group of species which we assign to the Mecopoda elongata group. Some species of this group have broad tegmina and stridulatory files with different tooth spacing patterns and produce continuous, often relatively complicated, trill-like songs. The species of another subgroup with narrower wings have all similar files. Their songs consist of echemes (groups of syllables) which differ in syllable number and syllable repetition rate and also in echeme repetition rate. Our results show that South East Asia harbours a large and certainly not yet fully explored number of Mecopoda species which are most easily and clearly identified by song. Based on the data, five new forms are described: Mecopoda mahindai Heller sp. nov., Mecopoda paucidens Ingrisch, Su & Heller sp. nov., Mecopoda sismondoi Heller sp. nov., Mecopoda niponensis vietnamica Heller & Korsunovskaya subsp. nov., Eumecopoda cyrtoscelis zhantievi Heller subsp. nov. In addition, some taxonomic changes are proposed: Eumecopoda Hebard, 1922 stat. rev., Paramecopoda Gorochov, 2020, syn. nov. of Eumecopoda Hebard, 1922, Mecopoda javana (Johansson, 1763) stat. nov. (neotype selected) with M. javana minahasa Gorochov, 2020 stat. nov., M. javana darevskyi Gorochov, 2020 stat. nov., M. javana buru Gorochov, 2020 stat. nov., Mecopoda macassariensis (Haan, 1843) stat. rev., Mecopoda ampla malayensis Gorochov, 2020 syn. nov., Mecopada ampla javaensis Gorochov, 2020 syn. nov., Mecopoda fallax aequatorialis Gorochov, 2020 syn. nov., the last three are all synonyms of Mecopoda himalaya Liu, 2020, Mecopoda yunnana Liu 2020, stat. nov.

Solifugae, also known commonly as sun spiders or camel spiders, are spider-like arachnid predators commonly present in desert and arid environments, though they also occur in forests and grasslands...

Blue catfish Ictalurus furcatus, the largest catfish in North America and an invasive species in Chesapeake Bay estuaries, has experienced explosive population growth, negatively impacting native species. They have strong pectoral spines that can be locked and rubbed against the pectoral girdle to produce stridulation sounds although sound production during behavioral interactions is unstudied. We examined agonistic behavior in juveniles by allowing individuals to establish a territory and introducing an intruder. Big (43–50 cm total length) and small (36–41 cm) fish were paired within and across size ranges. Territory was considered established when a fish remained in its shelter for over an hour. Fish typically entered the shelter head first and maintained that orientation. They used a variety of agonistic behaviors in shelter defense including aggressive contact, caudal sweeping, and standoff but not the production of stridulation sounds. Individuals often utilized different behaviors indicating less stereotypy than in many fishes, and there were differences in incidence of behaviors between big and small fish. Residents and larger fish did not always win, perhaps due to juvenile status and low fitness consequences of territorial possession.

Stridulation is a type of communication in which a mechanical signal is emitted by the friction of two rigid structures. Stridulation is present in kissing bugs (Reduviidae: Triatominae), where the...

Male Katydids (Orthoptera: Tettigoniidae) rub together their specialised forewings to produce sound, a process known as stridulation. During wing closure, a lobe on the anal margin of the right forewing (a scraper), engages with a teeth-covered file on the left forewing. The movement of the scraper across the file produces vibrations which are amplified by a large wing cell adjacent to the scraper, the mirror. Katydids are known to stridulate with either sustained or interrupted sweeps of the file, generating resonant pure-tone (narrowband frequency) or non-resonant (broadband frequencies) calls. However, some species can conserve some purity in their calls despite incorporating discrete pulses and silent intervals. This mechanism is exhibited by many Pseudophyllinae, such as Nastonotus spp., Cocconotus spp., Triencentrus spp. and Eubliastes spp. This study aims to measure and quantify the mechanics of wing stridulation in Nastonotus foreli, a Neotropical katydid that can produce complex, relatively narrowband calls at ≈20kHz. It was predicted that this species will use a stridulatory mechanism involving elastic energy whereby the scraper bends and flicks along the file in periodic bursts. The calling behaviour and wing mechanics of seven males were studied using a combination of technologies (e.g. micro-scanning laser Doppler vibrometry, advanced microscopy, ultrasound-sensitive equipment and optical motion detectors) to quantify wing mechanics and structure. Analysis of recordings revealed no clear relationship between wing velocity and carrier frequency, and a pronounced distinction between wing velocity and scraper velocity during wing closure, suggesting that the scraper experiences considerable deformation. This is characteristic of the elastic scraper mechanism of stridulation. Curiously, N. foreli might have evolved to employ elastic energy to double the duration of the call, despite possessing muscles that can reach velocities high enough to produce the same frequency without the help of elastic energy.

This review addresses the history of neuroethological studies on acoustic communication in insects. One objective is to reveal how basic ethological concepts developed in the 1930s, such as innate releasing mechanisms and fixed action patterns, have influenced the experimental and theoretical approaches to studying acoustic communication systems in Orthopteran insects. The idea of innateness of behaviors has directly fostered the search for central pattern generators that govern the stridulation patterns of crickets, katydids or grasshoppers. A central question pervading 50 years of research is how the essential match between signal features and receiver characteristics has evolved and is maintained during evolution. As in other disciplines, the tight interplay between technological developments and experimental and theoretical advances becomes evident throughout this review. While early neuroethological studies focused primarily on proximate questions such as the implementation of feature detectors or central pattern generators, later the interest shifted more towards ultimate questions. Orthoptera offer the advantage that both proximate and ultimate questions can be tackled in the same system. An important advance was the transition from laboratory studies under well-defined acoustic conditions to field studies that allowed to measure costs and benefits of acoustic signaling as well as constraints on song evolution.

Social insects communicate by using chemical, visual, tactile, and acoustic signals, including stridulations. Ectatomma ruidum is a mainly Neotropical ant species complex that has faced strong divergence at the genetic level; the species have a highly variable blend of cuticular hydrocarbons and a relatively conserved morphology. Based on evidence for genetic and chemical differentiation, we tested for variation in acoustic traits. We compared the stridulations produced by the species E. ruidum sp. 2, sp. 3–4 and the new putative species E. ruidum sp. 5, as well as the morphology of the stridulatory file. We found that the stridulations produced by E. ruidum sp. 5 were statistically different from those of the other species in a number of traits. The differences in stridulatory traits might rely more on the way the ants produce the sound (rubbed area percentages) than on the morphology of the stridulatory file, for which we did not find variation. Our results highlight the use of acoustic traits as potential taxonomic tools for integrative taxonomic studies and suggest that the acoustic traits of E. ruidum species complex have been subjected to selection.

Simple Summary Acoustic technology is a potential tool to protect wood materials and live trees from colonization by bark beetles and other wood-infesting insects. Bark beetles such as the pinyon engraver beetle Ips confusus use chemical and acoustic cues to communicate and to locate potential mates in trees. In this study, we describe the structures and airborne sounds produced by the pinyon engraver beetle, and test the efficacy of vibroacoustic treatments for tree protection against this beetle. Only female beetles possessed sound producing structures, located on the back of the head and inside the thorax. We analyzed and described the airborne sounds, called chirps, produced by females when held by tweezers or placed on their back. We tested a wide variety of vibroacoustic treatments played into logs but these sound treatments did not prevent male entry into logs and did not disrupt female–male interactions, female tunneling behavior, reproduction or egg laying. We suggest further studies if acoustic methods are to be utilized to control this bark beetle. Abstract Bark beetles are among the most influential biotic agents in conifer forests, and forest management often focuses on bark beetle chemical communication for tree protection. Although acoustic communication occurs in many bark beetle species, we have yet to utilize acoustic communication for bark beetle control. Here, we describe the stridulatory organs and ‘stress’ chirps of the pinyon engraver, Ips confusus, a significant pest and mortality agent of pinyon pine in western North America. Only females possessed stridulatory organs and their stress chirps varied significantly in duration, pulses per chirp, and dominant frequency. We tested an array of acoustic-vibrational treatments into logs but were unable to disrupt male entry into logs or alter female–male interactions, female tunneling, and female oviposition. We found acoustic–vibrational treatments had little effect on I. confusus behavior and suggest further studies if acoustic methods are to be utilized for bark beetle control.

On the basis of the song and morphological analyses, we revised the status of the subspecies Stenobothrus eurasius eurasius Zubowsky, 1898, and S. eurasius hyalosuperficies Vorontsovskii, 1927. The status of the subspecies S. eurasius hyalosuperficies Vor. has been changed to the species level. The most striking difference between S. eurasius and S. hyalosuperficies lies in the song parameters. The calling songs differ not only in temporal parameters but are also produced by different mechanisms. S. eurasius generates calling songs by common leg stridulation, whereas S. hyalosuperficies produces sound by wing clapping. The courtship songs of both species are complex (contain several elements) and very different in temporal structure. The morphological differences between the two species are not as striking as the differences in bioacoustics: we found the only differences in the hind wing venation. At the same time, we suggest these differences to be important since they might be due to different mechanisms of sound production. We revised the ranges of the two species on the territory of Ukraine, Russia and Kazakhstan. We also reviewed the type localities of S. eurasius Zub. and designated lectotype and paralectotype of this species.

The family Theraphosidae is the most speciose in the infraorder Mygalomorphae Pocock, 1892 with over one thousand described species (World Spider Catalog 2021). The taxonomy of the group has been subjected to considerable attention in modern times, with a focus on delineation based predominantly on genital organ and stridulatory organ morphology which has shown promise, both alongside molecular methods (where possible) and as a stand-alone line of evidence, in stabilising the group (e.g. Hamilton et al. 2016; Fabiano-da-Silva et al. 2020; see also Sherwood 2020). The predominant reference to the family is as Theraphosidae Thorell, 1870 with almost as many references to Theraphosidae Thorell, 1869. This non-congruence of dates is because Tord Tamerlan Teodor Thorell (1830–1901) had his important work On European Spiders published in two parts during its publication by the Royal Society of Upsala in its journal Nova Acta Regiae Societatis Scientiarum Upsaliensis. The first half (pages 1–108 and the supplement I–XIII) was published in 1869 whereas pages 109–242 (despite being dated on the cover page as 1869) were published in 1870 (see Roewer 1942; Bonnet 1945; World Spider Catalog 2021). In the second part, the secretary of the society notes: “L’auteur avait proposé comme titre du présent mémoire: Remarks on Synonyms of European Spiders, preceded by some observations on Zoological Nomenclature and a Review of the European Genera of Spiders; mais, la partie, insérée dans le Tome VII, étant seule présentée à la Société des Sciences le 13 Fevr. 1869, il a été nécessaii’e d’y conformer le titre.” [= The author proposed as the title of this memoir: Remarks on Synonyms of European Spiders, preceded by some observations on Zoological Nomenclature and a Review of the European Genera of Spiders; but, the part, inserted in Volume VII, being the only one presented to the Société des Sciences on 13 Feb. 1869, it was necessary to conform the title to it.].

Synopsis There are at least eight ways that wings potentially produce sound. Five mechanisms are aerodynamic sounds, created by airflow, and three are structural sound created by interactions of solid surfaces. Animal flight is low Mach (M), meaning all animals move at

Insect defense sounds have been reported for centuries. Yet, aside from the well-studied anti-bat sounds of tiger moths, little is understood about the occurrence, function, and evolution of these sounds. We define a defense sound as an acoustic signal (air- or solid-borne vibration) produced in response to attack or threat of attack by a predator or parasitoid and that promotes survival. Defense sounds have been described in 12 insect orders, across different developmental stages, and between sexes. The mechanisms of defensive sound production include stridulation, percussion, tymbalation, tremulation, and forced air. Signal characteristics vary between species, and we discuss how morphology, the intended receiver, and specific functions of the sounds could explain this variation. Sounds can be directed at predators or non-predators, and proposed functions include startle, aposematism, jamming, and alarm, although experimental evidence for these hypotheses remains scant for many insects. The evolutionary origins of defense sounds in insects have not been rigorously investigated using phylogenetic methodology, but in most cases it is hypothesized that they evolved from incidental sounds associated with non-signaling behaviors such as flight or ventilatory movements. Compared to our understanding of visual defenses in insects, sonic defenses are poorly understood. We recommend that future investigations focus on testing hypotheses explaining the functions and evolution of these survival sounds using predator-prey experiments and comparative phylogenetics.

International audience; The ability to produce sounds for acoustic communication is well known in different grunt species (Haemulidae). However, most of the sounds have not been described and the sound-producing mechanism of very few grunt species has been deeply studied. Additional data is needed to search for synapomorphy in the sonic mechanism. This study describes acoustic features and branchial anatomy in Haemulon aurolineatum. Correlations were found between some acoustic features and standard length, showing the largest specimens produced shorter, lower-pitched grunts of higher intensity. Examinations of acoustic features and branchial anatomy show that H. aurolineatum uses the same stridulatory mechanism described previously in H. flavolineatum. The unusual feature of Haemulon species concerns the fourth ceratobranchials. These appear to be part of the lower pharyngeal jaws since they possess firmly attached teeth that face the upper pharyngeal jaws. The stridulation results from the rubbing of both pharyngeal and fourth ceratobranchial teeth. This mechanism is probably common to the 23 Haemulon species, but additional information is needed regarding the mechanism of other Haemulinae species to produce stridulatory sounds. Fourth ceratobranchials could constitute a key element of Haemulinae ability to produce sounds providing an eventual synapomorphic aspect of the mechanism in the family.

Insect societies require an effective communication system to coordinate members’ activities. Although eusocial species primarily use chemical communication to convey information to conspecifics, there is increasing evidence suggesting that vibroacoustic communication plays a significant role in the behavioural contexts of colony life. In this study, we sought to determine whether stridulation can convey information in ant societies. We tested three main hypotheses using the Mediterranean ant Crematogaster scutellaris: (i) stridulation informs about the emitter’caste; (ii) workers can modulate stridulation based on specific needs, such as communicating the profitability of a food resource, or (iii) behavioural contexts. We recorded the stridulations of individuals from the three castes, restrained on a substrate, and the signals emitted by foragers workers feeding on honey drops of various sizes. Signals emitted by workers and sexuates were quantitatively and qualitatively distinct as was stridulation emitted by workers on different honey drops. Comparing across the experimental setups, we demonstrated that signals emitted in different contexts (restraining vs feeding) differed in emission patterns as well as certain parameters (dominant frequency, amplitude, duration of chirp). Our findings suggest that vibrational signaling represents a flexible communication channel paralleling the well-known chemical communication system.