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Social Spider’s Fierce Behavior Discovered in 100-Million-Year-Old Fossil

Oct 09, 2012 08:13 AM EDT

A 100-million-year-old fossil of an orb-weaver spider attacking a parasitic male wasp has been discovered in a piece of amber. 

Experts found the amber (globules of fossilized resins) while excavating a mine in the Hukawng Valley of Myanmar. It dates back to the early Cretaceous period between 97 and 110 million years ago.

This is the first fossil evidence showing a remarkable event of a spider attacking a wasp in the web.  The amber has at least 15 unbroken strands of spider silk and the parasitic wasp was entangled in it.

According to the researchers the tree resin flowed on the spider and choked it to death just before it was about to consume its prey.  "This juvenile spider was going to make a meal out of a tiny parasitic wasp, but never quite got to it," George Poinar, Jr., a professor emeritus of zoology at Oregon State University, said in a statement.

"This was a male wasp that suddenly found itself trapped in a spider web. This was the wasp's worst nightmare, and it never ended. The wasp was watching the spider just as it was about to be attacked, when tree resin flowed over and captured both of them," Poinar summarized from the nature of the insects caught in the amber fossil.

Apart from the fossil evidence showing the predatory behavior of the spider, experts also found another male spider in the amber. The presence of two spiders in the same web suggests evidence of sociality in them.  

Both the spider (Geratonephila burmanica) and the parasitic wasp (Cascoscelio incassus) belong to the extinct genera. However, this type of wasp belongs to a group that is today known to parasitize the spiders and lay their eggs on them.

Amber is known to preserve specimens such as insects, spiders, flies and wasps. According to experts, amber helps in estimating the evolutionary changes over millions of years. The oldest known fossil of a spider web is 130 million years old.

The findings of the study, "Predatory behaviour of the social orb-weaver spider, Geratonephila burmanica n. gen., n. sp. (Araneae:Nephilidae) with its wasp prey, Cascoscelio incassus n. gen., n. sp.(Hymenoptera: Platygastridae) in Early Cretaceous Burmese amber", are published in the journal of Historical Biology.

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