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This spider survey of a semidecidual forest area in the city of Mendes, in Rio de Janeiro state, Brazil, aims to increase the scant knowledge about spider communities in this Brazilian ecosystem. Samples were taken over a year, once every three months, in four different sites with seven sampling methods. An overall of 457 species/morphoespecies were recorded in 47 families, corresponding to 10,541 individuals sampled. Families with highest number of species were Theridiidae (91), Araneidae (72), and Salticidae (55). Families with highest abundance were Theridiidae (2,829 specimens), Pholcidae (2,328), and Araneidae (1,263). Most abundant species were Mesabolivar togatus(534), Carapoia lutea(499 individuals), and Cryptachaea digitus (387). Species accumulation curves indicate a minimum of 513 (Bootstrap) and a maximum of 653 species (Jackknife2) for sampled areas. Total Berger-Parker dominance index was low, 0.051, varying from 0.042 to 0.076, while total Pielou equitability Index was high, 0.805, ranging from 0.744 to 0.800. Total Shannon-Wiener diversity index was relatively high, 4.931, ranging from 4.559 to 4.899. The complex, very diverse and relatively well-structured spider community found in Mendes is remarkable, especially in an area with predominantly secondary forests and high anthropic influence. [ABSTRACT FROM AUTHOR]

The density and age structure of spider populations are affected by biotic and abiotic factors. The orb-web spider Eustala taquara (Araneidae) lives camouflaged on the dead vegetation of shrubs, especially in forest edges. Here, we describe the variation in the number of individuals over the year and the phenology of a population of E. taquara. We also tested whether these variables are influenced by temperature, precipitation or prey availability. We conducted the research in a tropical rainforest located in south-eastern Brazil. We recorded the number of spiders and their development stages (spiderling, young, juvenile, sub-adult and adult) monthly, for two years, along 1 km at the forest edge at an altitude of 1000 m above sea level. We estimated prey availability using 20 circular transparent plates containing tanglefoot on one side, exposed for 48 hours in the vegetation, sampled monthly for 18 months. We used circular statistics to assess the peaks of individuals during the study period, verifying the occurrence of time lags between the number of spiders with the climatic variables and prey availability. The population of E. taquara increased in periods of lower precipitation and temperature, and decreased during the rainy season. Thus, the population showed a negative correlation with the climatic variables and potential prey availability. All instars were present simultaneously, revealing that spiders can reproduce at any time of year. During the dry season, the higher number of spiders may be related to the increase in branches and dead plants that provide camouflage against visually oriented predators and sites for web building, increasing the likelihood of obtaining food. [ABSTRACT FROM AUTHOR]

In this study we report the first case of an introduced alien host spider species being parasitized and manipulated by an ichneumonid wasp. Hymenoepimecis bicolor, previously described parasitizing exclusively Trichonephila clavipes (Araneidae), was observed parasitizing the European species Cyrtophora citricola (Araneidae) in southeastern Brazil. The cocoon web built by the parasitized spider is composed of a reduced horizontal sheet, which maintains the radial structure. The reduced number of radii and spirals probably reduce the chances of insect interception by these modified structures. In addition, the density of supporting threads is apparently very different between normal and modified webs. The cocoon web spun by C. citricola lacks the protective barrier structure usually observed in cocoon webs spun by parasitized females of T. clavipes. Our observations are in agreement with several predictions of the ecdysteroid hypothesis and represent an interesting opportunity for further investigation of interactions between these parasitoids and their spider hosts. [ABSTRACT FROM AUTHOR]

Body coloration of orb-web spiders was previously hypothesized to be attractive to insects, luring potential prey, or associated with protection against visually oriented predators. We combined manipulative experiments with spectral reflectance analyses to test the prey attraction hypothesis, using the araneid spider Gasteracantha cancriformis as a model. The study was conducted in a shaded environment, within a forest fragment of the Atlantic forest located in Southeastern Brazil. Insect interception on web surfaces displaying the dorsal section of G. cancriformis opisthosoma, which emits blue fluorescence and reflects light in the ultraviolet wavelength region, was higher than on surfaces displaying the spider's ventral section, or in webs without spiders. This study supports the prey attraction hypothesis by providing evidence that the color patterns of G. cancriformis dorsum improve prey interception by their webs. Fluorescence and achromatic cues are probably important to lure and attract potential prey. [ABSTRACT FROM AUTHOR]

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We describe a new genus and two new species of the spider family Uloboridae Thorell, 1869 from south-eastern Brazil. Uaitemurigen. nov. can be distinguished by the peculiar shape of the opisthosoma, the presence of flattened setae on the patella and tibia of all legs, the flattened embolus, presence of a tegular plate in the male palpus, and female genitalia with flattened copulatory ducts associated with inflated hyaline copulatory atria. The type species, Uaitemuri rupicolasp. nov., is described from males and females from lowland and montane forests throughout south-eastern Brazil. A second species, Uaitemuri demariaisp. nov., is based on a single male from a coastal forest in the state of São Paulo. Morphological and behavioural data support the monophyly of the genus and suggest it is closely related to Orinomana Strand, 1934, Polenecia Lehtinen, 1967, Hyptiotes Walckenaer, 1837, and Miagrammopes O. Pickard-Cambridge, 1870. Uaitemuri rupicola builds vertical orb webs with a spiral-free sector, as observed in some species of Araneidae and Tetragnathidae, but recorded here for the first time in Uloboridae. The pteromalid wasp Arachnopteromalus dasys Gordh, 1976 was observed attacking egg sacs in a population of U. rupicola. [ABSTRACT FROM AUTHOR]

We investigated the characteristics of the stabilimenta constructed by two species of Cyclosa, describing the variations within and among five populations. Both species constructed stabilimenta composed entirely of silk (linear and spiral types) or of silk and debris (linear, detritus clusters and complex types). The vertical linear detritus type was the most frequent structure for adult females of both species, whereas stabilimenta consisting of detritus clusters were more frequent for juveniles of C. morretes. The latter structures appeared to be an intermediate state towards the linear continuous type usually found in adults. The other types were rarely found, and silk stabilimenta were to be constructed only when detritus was not available. The substitution of silk by detritus indicated that both materials function as camouflage in C. morretes and C. fililineata webs. The positions occupied by the spiders within the detritus column (and in some cases the orientation of the stabilimenta) varied markedly within populations, and the unpredictability of their location could be important in reducing the risks of predation. The hypothesis that stabilimenta constitute defensive devices was indirectly corroborated by the observation that spider's body width and length were, respectively, strongly correlated with the width and length of the stabilimenta. [ABSTRACT FROM AUTHOR]

Baeus metazygiae sp. nov. is described as an endoparasitoid of the egg sacs of Alpaida veniliae (Araneidae) from Rio Grande, Brazil. A list of the neotropical species of Baeus is given including new distribution and host records. [ABSTRACT FROM AUTHOR]