What happens when an insect touches a spider’s web?
Most web-spinning spiders line their silken threads with droplets of glue, which snag blundering insects. But one group—the cribellate spiders—does something different. Their threads are surrounded by clouds of even more silk—extremely fine filaments, each a hundred times thinner than regular spider silk. These nanofibers give the silk a fuzzy, woolly texture, and since they have no glue, they’re completely dry. And yet they’re clearly sticky. Insects that stumble into the webs of cribellate spiders don’t stumble out again.
Raya Bott and colleagues at Aachen University in Germany have now shown that cribellate silk adheres to insects in a previously unknown and unsettlingly macabre way. When an insect touches the strands, waxy chemicals in its outer surface get sucked into the woolly nanofibers and reinforce them, turning the tangled mass of delicate threads into a solid, sturdy rope. The victim literally becomes a part of the web, inadvertently strengthening the instrument of its own capture.
Cribellate spiders are among the most ancient of spiders, and they use their silk in a variety of startling ways. The ogre-faced or net-casting spiders hold their webs in their front legs and drop them onto passing insects. The uloborid spiders have lost the venom that most spiders use, and instead crush their prey to death by wrapping them in excessive amounts of silk; one species was documented using 140 meters to envelop a single insect. And some uloborids—the triangle spiders—spin triangular bungee webs. They hold one corner in tension; when an insect lands, the spider lets go and the entire web collapses onto the target.