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Courtesy photo / OREGON STATE UNIVERSITY  

A spider attack is frozen in time for 100 million years.   


A 100-million-year-old dinner

by Mitch Smith
Oct 10, 2012


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Mitch Smith/MEDILL

The Field Museum's Paul Mayer prepares an arachnid fossil for a detailed photograph.

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Mitch Smith/MEDILL

The Field Museum's Paul Mayer holds a 300 million-year-old arachnid fossil found near Joliet.

The spider was about to pounce on the unsuspecting wasp snared in its web. But before that orb-weaver had a chance to dine, the prehistoric moment was frozen in time and buried in amber for 100 million years.

The resin likely fell from the tree, instantly killing both prey and predator just as the spider prepared to feast on the wasp, said George Poinar, an Oregon State University zoologist who studied the specimen.

“It’s funny in a way,” Poinar said. “Here’s a spider that made its web, was waiting for its prey. Finally, a wasp came along. Then it started toward the wasp and got preserved.”

The specimen – found seven or eight years ago in Myanmar – is nature’s version of an action photo.  It’s rare that fossils capture nature in motion, Poinar noted. Scientists say this find offers a new lens into the lives of the ancient insects.

“A lot of times you’re trying to deduce from physical adaptations what the behaviors were,” said Karen Kramer Wilson, a living invertebrate specialist at Chicago’s Peggy Notebaert Nature Museum. “To see the behaviors captured is really cool.”

 

After its discovery, the fossil made the rounds at several locations before landing in Poinar's lab. He co-authored a paper on the find in this month's edition of the journal Historical Biology.

In addition to the adult male spider preparing to eat the wasp, a juvenile spider was preserved on the web. Poinar said a third spider, a female that apparently avoided the carnage, made the web. While the fossilized spiders have bodies quite similar to today’s orb-weavers, Poinar said their social behavior is rare or absent in most modern spiders, which often engage in cannibalism. The web was likely hanging from the bark of a tree in a tropical or subtropical lowland forest at a time when dinosaurs still lived, Poinar said.

Closer to home, scientists have found spider-like insects dating back 300 million years. The bugs – which look like spiders and have eight legs but lack the ability to spin a web – were found near Joliet. Many are now housed at Chicago’s Field Museum. The Illinois fossils don’t depict scenes like the one found in Myanmar, but they are three times older and provide detailed contours of the insects.

“When these guys died, they fell into mud and conditions were just right,” said Paul Mayer, the Field Museum’s fossil invertebrate collections manager.

For the Myanmar fossil to form and survive, an even more unlikely chain of events had to unfold.

“It’s really one of these miracle pieces because the resin had to come just at the time the spider was attacking,” Poinar said. “It had to be complete, and it had to be found by some digger and, fourth of all, it had to be sent to scientists. What’s the probability of ever finding something else like that?”