Video: Assassin bugs ambush spiders in their own webs

Assassin bugs are just as cunning as they sound. The patient hunters stalk their dinners, ambushing unaware aphids and caterpillars before killing them with their beaks—piercing, sucking mouthparts they use to slurp up their target’s insides. But when they turn to another type of prey, a web-weaving spider, they face another challenge: sneaking up on the eight-legged morsels in their own webs. That’s an impressive feat because many spiders use their webs as extensions of their sensory systems. Now, scientists have figured out just how the assassin bugs stay under the radar. The gangly insects slowly grasp strands of web with their foretarsi—the tips of their front legs—and carefully pull them away from each other until they break, as shown in the video above. They then gently release the ends to minimize any telltale vibrations. By doing this, they can slice their way through the web, completely undetected, in a direct path to their prey. To measure the vibrations caused by this maneuver without touching the web, scientists used laser vibrometry, as they report today in Royal Society Open Science. Their measurements showed that the assassin bugs’ vibrations were virtually undetectable—revealing how these insects earned their name.