Spider Webs are extended Spider Brains and they suck Insect-Shells

Illu: Sineater for Quantamag

Vor ein paar Jahren durchschnitt Hilton Japyassú ein paar der Stränge in den Gebilden von Radnetz-Spinnen, so dass die Stränge zu Boden fielen – wo er Beutetiere (Grillen) platziert hatte. Ein paar der Spinnen waren nun dazu in der Lage, ihr zu Boden gefallenes „Restnetz“ so zu benutzen, wie es Cobweb Spinnen tun (die unregelmäßige Netze produzieren) und die Beute aktiv einzufangen. Dann fragte er sich, woher die Spinne die Information hat (das Netz anders zu nutzen, als ihre Evolution eigentlich vorsieht) und kam nun in einem neuen Paper zu dem Schluß: Bei zumindest diesem Spinnennetz handelt es sich um „Extended Spider Cognition“ – also eine Externalisierung ihres Gehirns. Und damit würden sie eine ähnliche Kognitions-Strategie fahren, wie etwa Oktopusse, deren Tentakel Teil des Wahrnehmungsapparats bilden.

Noch mehr News von Spinnennetzen der Cribellate Spinnen: Wenn sich ein Insekt in ihnen verfängt, löst das Spinnennetz den Chitin-Panzer der Tiere auf und verstärkt mit den Chemikalien die eigene Struktur. Deren Spinnennetze saugen also wortwörtlich die Haut ihrer Opfer vom Fleisch und fusionieren sie mit ihrem Netz (also auch ihrem externalisierten Teilhirn). Spiders are weird.

Atlantic: Does a Spider Use Its Web Like You Use Your Smartphone?
Paper: Extended spider cognition

Millions of years ago, a few spiders abandoned the kind of round webs that the word “spiderweb” calls to mind and started to focus on a new strategy. Before, they would wait for prey to become ensnared in their webs and then walk out to retrieve it. Then they began building horizontal nets to use as a fishing platform. Now their modern descendants, the cobweb spiders, dangle sticky threads below, wait until insects walk by and get snagged, and reel their unlucky victims in.

In 2008, the researcher Hilton Japyassú prompted 12 species of orb spiders collected from all over Brazil to go through this transition again. He waited until the spiders wove an ordinary web. Then he snipped its threads so that the silk drooped to where crickets wandered below. When a cricket got hooked, not all the orb spiders could fully pull it up, as a cobweb spider does. But some could, and all at least began to reel it in with their two front legs.

Their ability to recapitulate the ancient spiders’ innovation got Japyassú, a biologist at the Federal University of Bahia in Brazil, thinking. When the spider was confronted with a problem to solve that it might not have seen before, how did it figure out what to do? “Where is this information?” he said. “Where is it? Is it in her head, or does this information emerge during the interaction with the altered web?”

In February, Japyassú and Kevin Laland, an evolutionary biologist at the University of Saint Andrews, proposed a bold answer to the question. They argued in a review paper, published in the journal Animal Cognition, that a spider’s web is at least an adjustable part of its sensory apparatus, and at most an extension of the spider’s cognitive system.

The Atlantic: The Spider Web That Gets Stronger When It Touches Insects
Paper: Adhesion enhancement of cribellate capture threads by epicuticular waxes of the insect prey sheds new light on spider web evolution

Bott found a clue to cribellate silk’s powers by breaking out a powerful microscope. She noticed that whenever the silk had touched an insect, she couldn’t make out the individual nanofibers any more. It was as if they had fused together. She even filmed the process, showing that a wave of fusion begins at the point of contact, and then travels up the silk.

Looking more closely, she saw that the fibers were still there. They had just become embedded in some kind of fluid—think spaghetti strands drenched in a thick marinara sauce. And when she analyzed the chemicals in the fluid, she realized that it was a match for the waxes found in insect shells. It seemed like the silk absorbs these waxes right off the insects, just as cotton balls will soak up water. In the process, the silk reinforces itself.