An ancient piece of amber discovered during an expedition to India revealed the oldest-known example of a kind of parasitism known as “myrmecophily,” through the fossil of a 52-million-year-old beetle that likely made its living by mimicking ants.
Researchers think the fossil beetle, known as Protoclaviger trichodens, lived in the comfort of ant nests, an impostor passing itself off as a member of the nest, all while dining on ant eggs—an early example of the parasitic lifestyle still used by some species of beetles today.
“These beetles were right there inside the ant colonies, deceiving them and exploiting them.”
A study published in the journal Current Biology found that the rise of these stealthy beetles, which infiltrate ant nests around the world, took place alongside the ecological ascent of modern ants into the common insect they are today.
“Although ants are an integral part of most terrestrial ecosystems today, at the time that this beetle was walking the Earth, ants were just beginning to take off, and these beetles were right there inside the ant colonies, deceiving them and exploiting them,” said lead author Joseph Parker, a Museum research associate and postdoctoral researcher at Columbia University.
Today, there are about 370 described species belonging to Clavigeritae, a group of myrmecophilous, or “ant-loving,” beetles measuring about 1 to 3 millimeters in length.
Although Clavigeritae beetles are species-rich, they are quite rarely encountered in nature. The newly discovered specimen—brought to Parker’s attention by Museum Curator David Grimaldi, an expert in amber fossils—is thought to be the first fossil of this group to be discovered. The fossil was found in an amber deposit in what was once a rain forest environment in modern-day India, which was uncovered during a Constantine S. Niarchos Expedition supported by the Stavros Niarchos Foundation.
Modern Clavigeritae beetles use a suite of remarkable adaptations to bypass the fortress-like security of ant nests, which use pheromones to identify, and then dismember and consume, intruders. Using methods that scientists are still trying to understand, Clavigeritae beetles are able to pass through these defenses unhindered and integrate themselves seamlessly into the life of a colony.
“Adopting this lifestyle brings lots of benefits. These beetles live in a climate-controlled nest that is well protected against predators, and they have access to a great deal of food, including the ants’ eggs and brood, and, most remarkably, liquid food regurgitated directly to their mouths by the worker ants themselves,” Parker said.
Although the body of the newly discovered Protoclaviger specimen is very similar to modern Clavigeritae beetles, some of its characteristics are clearly more primitive. For example, the fossil’s abdominal segments are still distinct, whereas in modern beetles they are fused together into a single segment resembling a shield.
“Protoclaviger is a truly transitional fossil,” Parker said. “It marks a big step along the pathway that led to the highly modified social parasites we see today, and it helps us figure out the sequence of events that led to this sophisticated morphology.”