August 1, 2010 1 Comment
The soldier vs. the cockroach
About 100 million years ago, a soldier beetle of an ancient type found itself under investigation by the antennae of a much larger animal, possibly a giant cockroach. Understandably alarmed, the small soldier beetle, only about a quarter of an inch long, immediately fired off a shot of offensive chemical from one of its rear glands. Just as it released its toxic dose, a wave of sap engulfed it, forever freezing the moment in amber and taking with it the antennae of the larger predator.
We would never know a thing about this tiny event from millions of years ago were it not for the preservative properties of amber. It starts out as sap dripping down a tree but has captured for us some of the most amazing, ancient finds in the history of fossils. Recent reports have included the discovery of the oldest bee species and even the presence of the malaria pathogen in the blood of an amber-preserved mosquito. Finds like this make amber a window into an ancient world showing us things we otherwise would never see.
Small-scale wars in a big world
The scene between the cockroach and the soldier bug would have been lost to history without the amber. But now we know that chemical warfare, today widely practiced by a variety of insect species, existed at the time of the dinosaurs. As Tyrannosaurus rex made its way across the landscape leaving its tri-toed footprints in the mud, soldier beetles were busy waging their war against killers on a much smaller scale.
Insects today employ this tactic so frequently that it featured as the central trait of the most frightful insect villain in movie history, the sulfuric-acid squirting super-killer in the Alien series. Some modern insects do actually shoot acid as a form of defense; in fact, the modern version of the soldier beetle fires off a mean shot of carboxylic acid at anything trying to eat it. Other nasty mixtures insects use today include chemicals that make the predator vomit or at least spit out the intended snack.
The amber that captured the David vs. Goliath battle between the hapless soldier beetle and its cockroach attacker was found in an amber mine in Myanmar, formerly Burma. This mine has been a treasure trove of biological finds trapped in amber, discoveries that tell us things about ancient ecosystems that we otherwise never would know.
What we do know is that this ancient species of soldier beetle liked to eat aphids, other little insects, and plant pollen, which may have been why it was on the tree in the first place. It had seven pairs of chemical-firing glands along its abdomen and was able to pick and choose which ones to use, depending on the angle of the predator. In the case of the amber-encased soldier beetle, it was employing only one gland and had actually achieved a successful shot, engulfing the predator’s antennae in the presumably noxious chemical before succumbing to the flowing sap.
Don’t crack my amber!
No one knows exactly what the chemical was because the person who owns the amber and the scientist who discovered the beetle refuse to allow eager entomologists to examine the encased remains. Many entomologists would be thrilled to extract DNA from this specimen, to be able to compare it to other sequenced ancient and modern samples. Others would like to identify what this earliest known practitioner of chemical warfare was using in those seven accurately firing glands. But to get at these samples, the entire specimen would have to be ground up and completely destroyed, something the amber’s owner, a collector of such pieces, refuses to allow.
And, for the geeks…a new dating for the soldier beetle?
As consolation, entomologists will have to accept another prize. This particular fossil pushes the dating of this species of soldier beetle back by 60 million years, newly placing the little bug squarely in the time of the dinosaurs.