The tiny soldier beetle was under attack, probably by a giant cockroach, when sap trickled down the tree and entombed the beetle and part of the roach during the oldest case of chemical warfare ever discovered. That was 100 million years ago, and the story of the conflict, and the sophisticated defenses available to the beetle, remained undisturbed for all that time in a bed of amber in Burma's Hukawng Valley.
Miners looking for gems stumbled across the bed recently, providing a priceless new tool that is helping scientists piece together the story of life at the time of the dinosaurs.
George Poinar, Jr., a zoologist at Oregon State University in Corvallis, has acquired a number of rare specimens from the new mine, some even showing that malaria was thriving 100 years ago, but his favorite is the small chunk of amber that tells the story of the soldier beetle and the roach.
"This is a rare specimen," he said. "It's one of a kind. In 10 lifetimes I would probably never come across another one like this."
The beetle is actually owned by an amber collector, Ron Buckley, co-author with Poinar of a report on the research in the current issue of the Journal of Chemical Ecology. The piece is so priceless that Poinar and his colleagues have turned down frantic requests from other scientists who would like to grind up part of the beetle and sample its DNA and figure out its chemical defenses. It's just too valuable to sacrifice.
Poinar said he was stunned when he got his first look at the beetle.
"When I looked at it under the microscope I thought, oh my goodness, this is a beetle that is actually shooting out something. It has seven pairs of glands along the abdomen and it's shooting some chemical out of one of them." The chemical, which the scientists believe was toxic, covered the antenna from a foreign insect that apparently abandoned the attack. So the beetle survived, only to be entombed in the amber, along with the antenna.
"This beetle was being probed, probably by a giant cockroach that was ready to eat it when the beetle decided to get out its mace and start using it," Poinar said. This was a David and Goliath conflict. The beetle was only about a quarter of an inch long. Its attacker was about two to three inches long.
Chemical defenses are common today among many animals and insects, and even some plants, but Poinar said it's surprising to learn that they were around so long ago.
"Beetles do the same thing today, but no one thought that they evolved this defense 100 million years ago," Poinar said. In fact, this discovery more than doubles the age of soldier beetles, and they survived through the age of the dinosaurs.
And the tiny beetle entombed in Buckley's piece of amber is so similar to modern soldier beetles that even an amateur bug collector would probably know it was a beetle, and most likely a soldier beetle, Poinar said.
And even though this particular beetle died 100 million years ago, its story is being told today because of the remarkable qualities of a kind of tree sap that turns into amber. It's found mainly in three areas, the Baltic region, the Dominican Republic, and now the mine in Burma. It's extremely valuable to scientists because it doesn't just tell part of the story, like most fossils. It tells the whole story.
"It preserves a tremendous amount of detail," Poinar said. "You can even find a fly inside a spider web inside of amber. It entombs very fragile organisms, including microbes."