Working as a whole, ants seem to have their act together. They lead highly complex social lives with each performing specific tasks to help provide for the colony. Some species take advantage of this and parasitize the colony. This type of dependence on ants is called myrmecophily, and the oldest known example of this was recently discovered within a piece of amber from the Eocene. The research was led by Joseph Parker of the American Museum of Natural History, and the paper was published in the journal Current Biology.
There are over 370 species of myrmecophilous beetles within the Clavigeritae group. They are relatively small, typically ranging from one to three millimeters in length. This new species, Protoclaviger trichodens, was determined to be about 52 million years old. It was discovered in India, though the environment was much closer to a rainforest when P. trichodens lived.
Though ants are typically very adept at keeping predators at bay, these beetles have evolved to blend in with the ants and take advantage of their resources. By secreting certain pheromones, the beetles can be seen and received by the ants as one of their own. Without this scent, they would be attacked and ultimately eaten.
"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," Parker said in a press release. "This tells us something not just about the beetles, but also about the ants -- their nests were big enough and resource-rich enough to be worthy of exploitation by these super-specialized insects. And when ants exploded ecologically and began to dominate, these beetles exploded with them."
Once inside the nest, the beetles pretty much had it made. The vast underground network protected them against the elements, and the ants would also provide defense for the beetle by killing any possible predator who did not emit the all-important pheromone password. In addition, without contributing anything themselves, they are able to access the food collected by the ants, and even dine on the eggs.
Because of this "wolf in sheep's clothing" approach, these myrmecophilous beetles don't look much like other beetles. Their mouths have been altered, allowing them to receive liquid food directly from worker ants, just like an ant. Ants sometimes carry the beetles with their mouths, so the beetles' body segments have been fused in order to provide extra armor. Specialized glands secrete the pheromones needed to infiltrate the ant nest, and specialized hairs help make the scent more prominent. Modern ants welcome these beetles warmly when greeting one another.
This fossil's age allows the researchers to discern more about how myrmecophilous beetles came about, and how their evolutionary changes correlate with the changes among ants. Though this specimen had features that were similar to current ant-parasitizing species, the body segments are clearly distinct. P. trichodens lacked that armored protection, though it did have the hairs that current myrmecophilous beetles use to transmit their pheromones."Protoclaviger is a truly transitional fossil," he concluded. "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."