Natures wonders: spider web shapes evolved (Introduction)

by David Turell @, Wednesday, October 31, 2018, 20:04 (323 days ago) @ David Turell

Spiders have been around for a very long time an d have chased insects as they learned to fly:

https://www.scientificamerican.com/article/sticky-science-the-evolution-of-spider-webs/...

"It may seem silly to fear a little spider—but the predator’s appearances in horror movies make more sense when you consider the precision, skill and creativity it employs to target its prey. Spiders’ venom-injecting fangs and the pointy claws tipping their segmented legs are menacing enough, but their innovative use of silk to ensnare victims may be the biggest reason to be grateful they are small.

“'They’re absolute masters of using silk,” says Paul Selden, an arachnologist and paleontologist at the University of Kansas. Other creepie-crawlies make the stuff, too—silkworms use it pupate in, some ants make nests from it—but, says Selden, “they don’t have the great variety of uses that spiders do.”

"Orb weavers, sometimes classified along with their descendants into a grouping called Orbiculariae, comprise about a quarter of the more than 45,000 known spider species. Their webs typically feature the classic concentric circle and spoke-like strands that radiate from a hub. But some Orbiculariae members spin novelties.

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"Scientists are still working to classify this diversity and understand how it got here, says Selden, who coauthored a review on spider web evolution in the Annual Review of Ecology, Evolution, and Systematics. This picture from the review hints at a general evolutionary progression as one moves up the tree, and highlights a pivotal event: As insects took to flight, spiders chased up after them, placing their snares higher in the air.

"The webs continued to diversify as insects evolved ways to escape this clade of predators. Scoloderus’ ladder web, which sports an elongated, crosshatched netting above a typical, circular orb, is specialized to target moths, which would normally escape a sticky web by shedding protective scales. The ladder portion keeps the moth tumbling—and will trap it when the scales have all flaked off. The triangle spider (Hyptiotes) optimizes its attack by releasing the long-thread portion of its web when an insect hits the main, cone-shaped portion. As a result, the web collapses and envelops the target, like a camping tent that has suddenly lost its poles.

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"Clues about the evolution of web-building behavior have come in part from fossil evidence. Webs and other silken structures typically don’t fossilize well (though occasionally, scientists have found strands of silk and clumps of web preserved in amber), so researchers often rely on the connections they can make between present-day spider morphology and behavior to tell them something about spiders and proto-spiders of the past.

"For example, today’s sheet web builders (such as the Agelena group pictured, and funnel-web spiders of the Ischnothele genus) lay blankets of webbing across grass and other vegetation and tend to exhibit unusually long spinnerets. Just this year, scientists noted similarly long spinnerets in the recently discovered fossilized remains of ancient arachnids. Thus, “at least one hypothesis would be that they built a type of sheet web,” says Bond. “Maybe sheet webs are the type of web that’s ancestral for all spiders.”

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"The mind-boggling diversity of spider strategies shouldn’t come as such a surprise when one considers that they have had hundreds of millions of years to evolve—researchers have found fossils of spiders that were scuttling around more than 150 million years before the dinosaurs.

“'You’re talking about 50,000 species of things that are all nearly exclusively predatory,” says Bond. “Spiders have devised all sorts of ways of killing insects.'”

Comment: The intricate geometric designs of the webs suggest these guys were helped in their designs as ell as the different forms of their silk..


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