Increasing performance in spider orb webs (Larinioides cornutus) intercepting high speed prey

Spider orb webs (Araneidae) dissipate the mechanical energy of their flying prey, bringing the insects to rest and retaining them long enough for the spider to attack and subdue their meals. Small prey is easily stopped by webs but provide little energetic gain. While larger prey offer substantial nourishment they are also challenging to capture and can damage the web if they escape. We therefore hypothesized that spider orb webs exhibit properties that improve their probability of stopping larger insects while minimizing damage when their mechanical energy exceeds the web’s capacity. Large insects are typically both heavier and faster flying, but speed plays a disproportionate role in determining total kinetic energy so we predicted that orb webs may dissipate energy more effectively under faster impacts. We used high speed video to visualize the impact of wood pellets fired into orb webs to simulate prey strikes and test how capture probability varied as a function of pellet size and speed. Capture probability was virtually nil above speeds of about 3 m/s. However, for at least some size classes of prey, we found that capture probability increased significantly with “flight” speed of the pellets. However, successful captures do not directly measure the maximum possible energy dissipation by orb webs. Therefore, we also compared the total kinetic energy removed from pellets that escaped orb webs by breaking through the silk, asking whether more energy is removed at faster speeds. Over a range of speeds relevant to insect flight, the amount of energy absorbed by prey breaking through webs increases with the speed of prey (i.e. the rate at which webs are stretched).  Orb webs therefore respond to high energy prey with better performance, suggesting adaptation to capture extreme prey. We conclude that orb webs function better at removing prey energy at higher flight speeds. This speed dependent toughness of a complex structure suggests the utility of either the intrinsic toughness of the silk  and/or some feature of the macro-design of webs in high velocity industrial or military applications such as ballistic energy absorption.