April Flowers for redOrbit.com – Your Universe Online
Researchers at Oregon State University have found an extraordinarily rare fossil. Trapped in amber is what the research team describes as the only example of a spider attack on prey caught in its web — a 100 million year old snapshot of an engagement frozen in time.
Found in the Hukawng Valley of Nyanmar, the fossil dates from the Cretaceous between 97 and 100 million years ago. Giving some evidence to oldest examples of spider social behavior, the amber contains not only the spider attacking the prey, but also another male spider in the same web. This behavior exists today, but is rare. Instead, most spiders live solitary, almost cannibalistic existences, and males will not hesitate to attack immature species in the same web.
“This juvenile spider was going to make a meal out of a tiny parasitic wasp, but never quite got to it,” said George Poinar, Jr., a professor emeritus of zoology at Oregon State University and world expert on insects trapped in amber.
“This was a male wasp that suddenly found itself trapped in a spider web,” Poinar said. “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.”
Researchers believe that spiders are ancient invertebrates that date back some 200 million years. The oldest fossil evidence found of a spider, however, is only about 130 million years old. This type of fossil, showing an attack between a spider and its prey has never been documented before.
Amber is made from a tree resin that is renowned for its ability to flow over insects, small plants and other life forms. This preserves them in near perfection before turning into a semi-precious stone. Amber often gives scientists their clearest look into the biology of the past. The spider in this sample, which may have been patiently waiting for hours to capture prey, was smothered in resin just a split second before its attack on the wasp.
The wasp in the fossil is of a type known today to parasitize spider and insect eggs, so the attack by the orb-weaver spider could be considered payback. Both spider and wasp belong to extinct genera. At least 15 strands of unbroken spider silk shoot through the amber.
The findings of this research have been published in the journal Historical Biology.