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These Beetles Have Been Evil Ant Overlords for 52 Million Years

Fossilized amber from the Eocene proves that these beetles have a long history of freeloading off of ants while eating their babies. Deception level: Clavigerite.
Protoclaviger trichodens: apex freeloader. Image: AMNH/J. Parker

A chunk of Eocene amber found in India has revealed that clavigerite beetles have been diabolically mooching off of ants for at least 52 million years and counting. These beetles have evolved the bizarre ability to produce pheromone passcodes that give them free reign of ant colonies—including access to the nests, where the beetles unrepentantly dine on their hosts' babies.

This definitely puts the clade into the running for "worst guests ever," and the fossilized amber tableau presents a unique window into the early days of their parasitic behavior.

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Paleontologists based out of the American Museum of Natural History published an analysis of the specimen in the journal Current Biology today, and it is packed to the brim with weird insights about the development and behavior of these "myrmecophiles" (a broad term for species that benefit from ants).

The beetles also employ curious behaviors, mounting and riding ants around the nest and twirling their antennae at passing workers

"We believe just like modern relatives, this fossil beetle was fully able to infiltrate colonies and deceive the host ants into accepting it as a nest mate," lead author Joe Parker told me.

For example, let's reflect on the following passage from the paper: "Clavigerite beetles are treated as ant nestmates and are entirely dependent on their hosts," it reads. "They are fed by worker ants via stomodeal trophallaxis (mouth-to-mouth liquid feeding) and are transported in worker mandibles and deposited in colony brood galleries, where they feed on ant eggs and cuticular secretions from ant larvae."

So not only do these freeloaders eat ant babies, they are carried around like royalty to these infanticidal feedings. Aside from juvenile ants, the other option on the menu is food taken literally out of the mouths of their ant minions. Anthropomorphizing animals is never a good idea, and yet it's difficult to avoid admiring these beetles for their nerve.

Modern clavigerites being carried around by ants. Image: Takashi Komatsu, provided by AMNH

It actually gets better—unless you're an ant. Further on in the study, the authors write that "[t]he beetles also employ curious behaviors, mounting and riding ants around the nest and twirling their antennae at passing workers. In possibly the most extreme cases of obligate myrmecophily known, some Clavigeritae are completely eyeless and wingless and may disperse phoretically on queen ants during the nuptial flight."

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Again, at the risk of anthropomorphizing the insects, clavigerite beetles are as close to the "evil overlord" archetype as an insect is likely to get. They even have the gall to tag along with queen ants on their wedding nights.

The AMNH team were able to determine that this parasitic relationship was already in full swing when the clavigerite ancestor discussed in the study, named Protoclaviger trichodens, was trapped in the resin of an Eocene tree.

This photo shows some of the diversity of modern Clavigeritae beetles. Image: AMNH/J. Parker 

"It has a whole suite of features that are clear adaptations for this lifestyle," Parker said, "such as modified mouthparts (to receive liquid food mouth-to-mouth), partial fusion of antennal segments (to strengthen these exposed appendages for when ants pick up the beetle and carry it around in their mandibles), and brush-like trichomes; which in modern species exude chemicals that ants find irresistible and which seem to behaviorally manipulate the ants into accepting the beetle into the life of the colony."

Based on this advanced morphology, Parker and his colleagues estimate that the origins of Clavigerite beetles goes back about 73 million years, to the late Cretaceous, and that they have more or less coevolved with ants since that period.

The authors also speculate that the current diversity of clavigerites is partially owed to a spat of global warming during the Paleocene-Eocene Thermal Maximum, which occurred about 55 million years ago. Temperatures during the PETM rose as high as eight degrees Celsius, allowing ants and their myrmecophile hangers-on to expand their range into previously uninhabitable areas.

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And as ants diversified, so did the clavigerites, with a current species count of 396, "and several times this number awaiting description," according to the study.

Clavigerites are just one group of about 10,000 extant myrmecophile species, but they are certainly among the most memorable of the ant-loving category. The discovery that their exploitation of ants dates back to the age of the dinosaurs goes to show that even socially intelligent insects can be hardcore duped by opportunistic parasites.

"The fact that these kinds of beetles are usually rare in nature seems to suggest that ants have done quite a good job of protecting their colonies from such parasitic intruders," Parker said. "It's a real evolutionary feat to be able to do what these beetles do—to not only bypass the ants' recognition system, but also effectively convince the ants to feed and treat you like you're a welcome guest."

"That's why these beetles appear so bizarre," he added, "because their environment is so extreme with intense selection pressures."

To sum up, clavigerites definitely lower the bar for houseguests everywhere. So the next time someone overstays his or her welcome in your home, just be glad they're not demanding piggyback rides to the nursery to cannibalize your children.