Predator perception of detritus and eggsac decorations spun by orb-web spiders Cyclosa octotuberculata:Do they function to camouflage the spiders?
<正> Camouflage is one of the most widespread and powerful strategies that animals use to make detection/recognitionmore difficult. Many orb-web spiders of the genus Cyclosa add prey remains, plant debris, moults, and/or eggsacs to their webscalled web decorations. Web decorations resembling spider body colour pattern have been considered to camouflage the spiderfrom predators. While this camouflage is obvious from a human's perspective, it has rarely been investigated from a predator'sperspective. In this study, we tested the visibility of web decorations by calculating chromatic and achromatic contrasts of detritusand eggsac decorations built by Cyclosa octotuberculata, against four different backgrounds viewed by both bird (e.g., blue tits)and hymenopteran (e.g. wasps) predators. We showed that both juvenile and adult spiders on webs with detritus or egg-sac decorationswere undetectable by both hymenopteran and bird predators over short and long distances. Our results thus suggest thatdecorating webs with detritus or eggsacs by C. octotuberculata may camouflage the spiders from both hymenopteran and birdpredators in their common habitats [Current Zoology 56 (3): 379-387, 2010].