Mind-Manipulating Slave-Making Ants!

An entire colony enslaved by an alien species to care for their young. Slave rebellions quelled by mind manipulation. It sounds like science fiction, right? But it really happens!

Myrmoxenus ravouxi (called M. ravouxi for “short”) is a slave-making ant species in which the queen probably wears a chemical mask, matching the scent of a host species in order to invade their nest without detection. Once inside, she lays her eggs for the host species workers to care for. Armies of M. ravouxi workers then raid these host colonies to steel their brood to become future slave-laborers to serve the needs of the M. ravouxi colony.

A M. ravouxi queen throttling a host queen. Photo by Olivier Delattre.

Enslaved worker ants could rebel: They could destroy the parasite brood or at least not do a good job caring for them. But to selectively harm the parasite brood without harming their own nests’ brood, the host ants would have to be able to tell them apart. Ants learn the smell of their colony in their youth, so any ants born to an already-parasitized colony would likely not be able to tell apart parasite ants from their own species. But what about ants that were born to colonies before they were invaded?

Olivier Delattre, Nicolas Châline, Stéphane Chameron, Emmanuel Lecoutey, and Pierre Jaisson from the Laboratory of Experimental Ethology in France figured that compared to ant species that were never hosts to M. ravouxi colonies, ant species that were commonly hosts of M. ravouxi colonies would be better able to discriminate their own species’ brood from M. ravouxi brood. Host species may even be better at discriminating in general.

The researchers collected ant colonies from near Fontainebleau and Montpellier in France. They collected M. ravouxi colonies and colonies of a species that they commonly parasitize (but were not parasitized at the time): Temnothorax unifasciatus (called T. unifasciatus for “short”). The researchers also collected T. unifasciatus that were parasitized by M. ravouxi at the time. Additionally, they collected colonies of T. nylanderi and T. parvulus, two species that are never parasitized by M. ravouxi. (Sorry guys. All these species go by their scientific names. But really, that just makes them sound all the more mysterious, right?). The researchers took all their ant colonies back to the lab and housed them in specialized plastic boxes (i.e. scientific ant-farms).

On the day of the tests, the scientists removed a single pupa (kind of like an ant-toddler) from one nest and placed it into a different nest of the same species or back in its own nest. They did this for colonies of both non-host species and for colonies of host species T. unifasciatus that were not parasitized at the time. Then they counted how many times the workers bit the pupa (an aggressive behavior) or groomed the pupa (a caring behavior).

Workers from all three species bit the pupa that was not from their colony more than they bit their own colony’s pupa. But the T. unifasciatus (the host species) were even more aggressive to foreign pupa than the other species. And only the T. unifasciatus withheld grooming from the pupa that was not from their colony compared to the one that was from their colony. Although all three species seemed to be able to tell the difference between a pupa from their own nest versus one from another nest, only the species that is regularly enslaved by M. ravouxi decreased care to foreign young. So that is what these ants do when they are not enslaved. How do you think enslaved ants respond to their own species’ young compared to M. ravouxi young?

A 1975 cover of Galaxie/Bis, a
French science fiction magazine,
by Philippe Legendre-Kvater.
Image from Wikimedia.

The researchers repeated the study using enslaved T. unifasciatus, placing either a pupa of their own species from a different nest or a M. ravouxi pupa in with their brood. Even though prior to M. ravouxi takeover the T. unifasciatus bit foreign pupa more than their own, after M. ravouxi takeover they didn’t bite foreign pupa of their own species or M. ravouxi pupa very much. Not only that, but they groomed the M. ravouxi pupa more than the pupa of their own species! Ah hah! Mind control!

This, my friends, is the kind of truth that science fiction is made from.

But how might this work? Ants born to an enslaved colony would be exposed to both their own odors and the M. ravouxi odors. Because ants learn the smell of their colony in the first few days after they emerge from their eggs, these enslaved ants would have a broader set of smells that they may perceive as being “within the family”. That would explain why the enslaved T. unifasciatus ants didn’t attack either the foreign-born T. unifasciatus or the M. ravouxi young, but it doesn’t explain why the enslaved ants provided more care to the M. ravouxi than they did to their own species. One possibility is that the M. ravouxi produce more or especially attractive odors to encourage the host workers to take care of them.

There is still more to learn about this system: How exactly may the M. ravouxi be hijacking the pheromonal systems of their host species? How are the host species protecting themselves from exploitation? I guess we’ll have to wait for the sequel.

Want to know more? Check this out:

Delattre, O., Chȃline, N., Chameron, S., Lecoutey, E., & Jaisson, P. (2012). Social parasite pressure affects brood discrimination of host species in Temnothorax ants Animal Behaviour, 84, 445-450 DOI: 10.1016/j.anbehav.2012.05.020