ScienceShot: How Spider Assassins Mimic Prey

Sometimes the spider becomes the prey. At least when assassin bug Stenolemus bituberus is on the job. The spindly-legged insect (pictured) lures arachnids to their deaths by landing on webs, struggling like entangled prey, and then eating the arachnids for dinner. To figure out how the deception works, scientists placed spider webs in a sound chamber and recorded the vibrations when an assassin bug, a falling leaf, a courting male spider, or one of two types of prey (vinegar fly or aphid) touched the web. Spiders' reactions to the assassins most closely mirrored those toward prey: turning, pausing, and approaching 65% of the time and turning but not approaching 35% of the time. However, the spiders never aggressively approached the assassin bugs, the researchers report online today in the Proceedings of the Royal Society B. The scientists think this reflects a deliberate tactic of the assassins. By making only short, low-frequency vibrations, the predators mimicked the struggles of small or exhausted prey, duping the spiders into letting down their guard.

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