Explosive Beetles Hack Ant Colonies for Royal Treatment

Guest blogging for Donovan is Dr. Wendy Moore of the California Academy of Sciences.

With roughly 350,000 described species, beetles are without a doubt one of the most successful forms of life on Earth. Many beetle species use chemicals to defend themselves, but the true masters of chemical defense are the Bombardier Beetles which deliver their defensive chemicals hot, really hot -- up to 212 degrees F (100 degrees C). Yes, that's right, there are beetles living right here in the San Francisco Bay Area that discharge chemicals at the boiling point of water! They have a two-chambered defensive gland and each chamber contains different chemicals. When mixed, the chemicals react with one another to produce so much heat that it literally explodes out of an opening on the abdomen, and kaboom! It's a built-in arsenal that deters nearly all predators.

I study a subgroup of these beetles known as the Flanged Bombardier Beetles. This group is incredible not only because they bombard, but also because most species live inside ant nests. That is particularly strange, because ants are extremely aggressive with fine-tuned strategies for keeping non-family members out of their nest. Normally foreigners that try to enter an ant nest are destroyed immediately. Although ants do not have good eyesight, they perceive the world through their sense of touch and taste. Colony members wear an invisible veil of chemicals, which allows them to recognize each other. When a non-family member is in the vicinity of a nest, ants attack first and ask questions later. But ant defenses are not foolproof and many species of Flanged Bombardier Beetles have managed to crack their secret chemical code.

For these clever beetles, going incognito is like going on an all-expenses-paid vacation. Ant nests are stable, dark, moist environments -- luxurious accommodations by insect standards. And since they don't have to worry about the ants themselves, the nests are virtually predator-free, making them safe places for adult beetles to lay their eggs and for their offspring to develop.

What's more, the beetles eat the ants and their eggs! Despite the fact that they are predators on ants, some behaviors of the host ants indicate that these beetles are not simply tolerated parasites of the ant colonies, but are valued by the ants in some way. For example, the beetles do not bomb their way into the nests, but rather the ants grab the beetles by their antennae and actively drag them inside.

What, if anything, do the ants get out of this arrangement? We do not know the answer to this question, but clues may be found in another chemical produced by the beetles. Species that live with ants have extremely modified antennae, with an astounding variety of shapes and sizes in different species. The antennae function like factories producing the substances that ants love to eat. Is it a drug? Is it food? We don't know. Whatever it is, it plays an important role in the establishment of beetle-ant relationships, and is one of the many intriguing mysteries I love exploring here at the Academy.

Dr. Wendy Moore is a postdoctoral fellow at the California Academy of Sciences, where her research focuses on the systematics and biogeography of the Flanged Bombardier Beetles of California and Madagascar.