Spatial distribution and substrate selection by the orb-weaver spider Eustala perfida Mello-Leitão, 1947 (Araneae: Araneidae)

Abstract

Spider habitat types are often restricted by specific biotic and/or abiotic factors. Abiotic physical limitations include temperature and humidity; and biological conditions influencing spider habitat include vegetation type, natural enemies and prey availability. The orb-weaver spider, Eustala perfida (Araneidae), typically builds its web against tree trunks, where it is highly camouflaged. In the present study, we evaluated E. perfida spatial distribution and substrate selection in Serra do Japi, an Atlantic Forest region located in Jundiaí (São Paulo, Brazil). We established plots within and at the forest edge at three altitudes, and measured trunk diameter, web height above ground level, presence of trunk concavities, and spider number in trees within plots. Eustala perfida occurred at all three altitudes, and was more common at the intermediate elevation. All individuals were observed within the forest interior, with the highest occurrence on trunks with diameter at breast height > 30 cm. Trunk diameter varied among sites, and E. perfida distribution apparently followed large trunk availability. On large diameter trunks, spiders typically placed their webs over concavities, and tended to build in rough areas covered by lichens and mosses at levels as high as ~ 150 cm above ground level. Selection of large rough trunks covered by lichens and mosses is probably an adaptation to remain concealed from visually oriented predators.

Keywords:

• habitat selection
• orb-weaver spiders
• camouflage
• Serra do Japi
• ladder-web

Acknowledgements

This project was supported by Instituto Nacional de Ciência e Tecnologia dos Hymenoptera Parasitoides da Região Sudeste (http://www.hympar.ufscar.br), Fundação de Amparo à Pesquisa do Estado de São Paulo (processes: 2011/02535-3, 2011/15457-0, 2011/15456-4 and 2011/02537-6) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (process: CRA 30058/12). We also thank Antonio Domingos Brescovit and Maria Rita M. Poeta for the identification of the spider species.