Spiders Use Airborne Cues to Respond to Flying Insect Predators by Building Orb‐Web with Fewer Silk Thread and Larger Silk Decorations

Orb‐web spiders are an important group of trap‐building animals that feed upon an array of insect prey and are themselves the prey of wasps and parasitoid flies. The purpose of this study was to examine whether spiders use airborne vibration cues to respond to these flying insect predators by changing their web‐building behavior. While on its web waiting for prey, the orb‐web spider Eriophora sagana was exposed to a vibrating tuning fork that emitted an airborne vibration signal. The signal mimicked the approach of flying insect predators and its effect on the subsequent web building was examined. No stimulus was provided during web building. A significant treatment effect was observed with respect to the total thread length (TTL) and area of the silk decoration (conspicuous white structure attached to the orb‐webs of diurnal spiders) of their webs. While control spiders increased the TTL in their second web, the stimulus group spiders did not, providing the first evidence that orb‐web spiders use airborne vibration cues to assess the predation risk and change their foraging activity. It also indicates that spiders remember an encounter with a predator on their webs and use this information later to adjust their web building. My findings imply that spiders devote less effort to foraging (i.e. web building) in response to the presence of their predators, which is considered to reduce their foraging efficiency. In contrast, the stimulus group spiders increased the area of their silk decoration significantly more in their second webs than did the control spiders. This is considered an experimental support for the hypothesis that silk decorations have an anti‐predator function.