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Ancient Web Weaves Tale of Spiders, Prey

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Times Staff Writer

A team of researchers has found a 110-million-year-old spider web embedded in a piece of amber -- the oldest known example of a web containing trapped insects.

It appears to be an orb web, like the spiral nets made by common garden spiders to catch flying insects, according to a report published Friday in the journal Science.

Caught within the tangles of the glue-dotted web were a fly, a mite, a beetle and a wasp leg.

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Team member David Grimaldi of the American Museum of Natural History in New York said that previously the oldest spider web found with prey attached was 20 million to 40 million years old.

The amber, found in Spain, is from the early Cretaceous period -- a time when dinosaurs roamed and insects were explosively diversifying.

The existence of orb webs during this period suggests that spiders and insects have been involved in a sort of arms race for a very long time, Grimaldi said.

As an example, he pointed out that during the Cretaceous period, butterflies and moths evolved to form loosely attached scales on their bodies and wings. These scales stick to webs and detach from the insects, allowing them to escape.

In a related study in Science, researchers reported that a genetic analysis of ancient spider silk showed that orb-weaving spiders evolved from a single species more than 136 million years ago.

The spiders fall into two groups: Araneoids weave sticky webs like the one found in the amber; deinopoids use a dry silk that is combed and looks like Velcro under a microscope.

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These silk differences led some scientists to believe that the orb web pattern evolved separately in these two groups -- a process known as convergent evolution.

But a genetic analysis of silk proteins conducted by UC Riverside evolutionary biologists Jessica Garb and Cheryl Hayashi and undergraduates Teresa DiMauro and Victoria Vo found that araneoids and deinopoids descended from a single ancient spider species.

Previously found fossils of the araneoid and deinopoid groups date back 136 million years, meaning that the common ancestor of orb weavers must have lived before this time, the report said.

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