There's an Ant for That

How to get ants to do your work for you—if you're an insect.

The original version of this article was published in Insects and That.

Ants: famously hardworking, loyal and abundant. Qualities that are good for the success of the giant family that constitutes a colony—but also looked upon fondly by those who would seek to exploit them. For all their collective smarts, ants are pretty prone to being fooled or cajoled; their efforts redirected into assisting other small creatures from outside their kin.

While the practice of myrmecophily literally means ‘ant love’, the reality of such life strategies cuts a bit deeper. It can involve anything from getting ants to care for young, snacking on ants' food or simply using ants' nests as shelter whilst avoiding a defensive reaction from the colony. A unique sort of love then; often unrequited.

Colonies are pretty much beset by such attachments. There are over 10,000 (known) arthropods, from pretty much all the orders, who can see ant nests as resources to exploit. Beetles, spiders, butterflies, lacewing—you name it—have all found keys for a grand entrance into ant society. The routes to achieving such objectives are varied.

Butterflies of the Maculinea genus go to among the most elaborate lengths to get ants to do their work for them. The use chemical signals that encourage Myrmica ants to escort their caterpillars to the nest and provide them with appropriate food plants.

Then, things can go even deeper.

Once in the nest, the caterpillars and pupae of some species of Maculinea have been shown to mimic the acoustic signals used by the queen. By making queen-like noises, these baby butterflies effectively hijack the queen's rank. This means worker ants go into a mode of ‘hyper benevolence’ towards them — even to the point of the caterpillars being rescued over the ants’ own brood, should a crisis which disturbs the nest occur.

Incredibly, the survival of different species of the butterfly are specifically linked to different ants. If a mother butterfly gets her egg-laying strategy wrong, it’s quite likely to be curtains for the caterpillars. A small victory amidst a deluge of deception, it could be argued.

Some scientists think the use of acoustic mimicry is also used by other ‘cuckoo’ arthropods seeking to loaf off the efforts of ants. If the chemicals don’t hook them in, the sounds, it seems, can be very effective.

A famous evolutionary ‘trick’ is used to great effect by some stick insects, which have adapted to lay eggs that look a lot like seeds — and not just any seeds either. The eggs of a number of species have what’s known as a ‘capitulum’, which resembles a seed structure of the kind ants like to bury. Except, instead of saving their seeds for the future, these ants are safely tucking away stick insect eggs for hatching.

This is a handy trick if you’re a ‘drop and go’ kind of parent. Indeed, such adaptations are only found in those stick insect species which freely drop their eggs onto the ground.

Pretty much every insect out there has its own egg parasite enemy, so naturally, eggs that end up in ants’ nests under false pretences have a much greater chance of surviving till they hatch.

Judging from an extremely anthropocentric position, the activities of ant nest beetles, found in the subfamily Paussinae, could be seen as a straight-up insult. These beetles are accepted in colonies, while preying on the ants’ young. They do this through a variety of means: as symphiles, meaning they secrete substances used as food for ants; through chemical signals that convince the ants they’re ‘one of them’, or simply having a body structure which ants can’t readily attack.

It’s not just other types of arthropod that want their ant-derived goods and services — there is also a solid strand of ‘ant on ant’ in the freeloading stakes, which tends to be rather more direct. There are a number of what is known as ‘slave-making’ ant species, which raid colonies of others and steal their young, subsequently putting those kidnapped ants to work in their own nests.

Protomognathus americanus is one of the most-studied of these raiders, and demonstrates some fascinating behaviours. For one thing, it has been shown to preferentially attack colonies with more workers: a strategy that offers much higher risk, but with also a greater reward of more pupae to haul off if they do manage to come out on top. Their attacks have a pretty high success rate, but don’t always come off.

Plus, there appears to be an even more ingenious way the ‘slaves’ fight back.

In the event of defences failing, once in the slave-maker’s nest, Temnothorax ants have been shown to kill off the young of P. americanus through recognition of their difference — a phenomenon that mirrors the approach some birds targeted by cuckoos use to kick out the parasite’s chicks after hatch. This example demonstrates a universal truth about animal relationships with their environment. When there is a push, there will always be some form of push back, through the good old evolutionary arms race.

The literature on arthropods — and indeed, plants, fungi and lots besides — that enjoy relationships with ants, whether with mutual benefits or without, is extensive to say the least. Should this brief highlights reel draw you in, there’s plenty of extended reading to dig into. This review paper is a great place to start.

Ultimately, if you put your own myrmecophile sympathies aside, you can see why ants are exploited to such an extent. At root, it’s all in the numbers: there’s an estimated 10,000 trillion of them on earth at any given time, equalling global human biomass.

That’s a lot of eager legs and mandibles to apply to tasks, whether strictly their own or others’.