These exploding ants take their colony’s defenses to the next level

Weaver ants are a mean bunch. They are not very large, but they are very aggressive and extremely territorial. Their main weapons are a pair of ferocious jaws; after biting, they also like to inject formic acid into the wound, just to shock. They go after other insects with particular vigor and are so good at killing their fellow mini beasts that weaver ant colonies are used as a form of biological pest control in the tropics.

So if you’re another kind of ant who shares the treetops with weavers, what should you do? It turns out the answer is simple: explode.

Okay, of course that sounds dramatic. But it is also literally true. When dealing with a threat such as the weaver ants, workers of some ant species inflate themselves, in a process known as autothysis. Basically, when these ants have enough trouble, they squeeze their internal organs so hard that they burst their exoskeleton, covering the environment with their guts.

The guts of ants by themselves are not enough to discourage weaver ants. Indeed, weavers are gut positive. But our exploding ants – to name them, they are… colobopsis explodes, which is Latin for “hey, these ants are exploding!” – not just be blown up for fun or as a quick escape from impending doom. These ants are basically stuffed up to the petiole with goopy venom, and when they explode, guess where all that goes? Yes. Everywhere.

Blowing themselves up in small poison bombs is an effective way for colobopsis ants to deal with threats that could otherwise be overwhelming. But autothysis is also a bit drastic. What makes these little critters sacrifice themselves in the face of the enemy? Surely their instincts would prevent them from doing such a thing? What about evolution? What about survival of the fittest?

This kind of behavior worried Charles Darwin when he was still writing About the origin of species. Not the behavior of the colobopsis ants themselves – to my knowledge he knew nothing about autothysis, which I suppose he would have enjoyed – but ants in general. Ants (and bees, wasps, termites, etc.) perform a range of behaviors that eusociality, which essentially involves cooperative care for young people and a sharp division between reproductive and non-reproductive individuals.

It’s that last part that Darwin really screwed up. In chapter eight of origin, he is writing:

I … will limit myself to one special difficulty, which at first seemed insurmountable to me, and actually fatal to my whole theory. I refer to the neuter or sterile females in insect communities: for these neuter animals often differ greatly in instinct and structure from both the male and the fertile females, and yet, being sterile, they cannot reproduce their species.

Darwin struggles to explain away the problem, and for a very good reason: Despite having evolved several times in different animal groups (my favorite is a species of sponge-dwelling shrimp from the Caribbean), eusocial behavior is extremely difficult to explain. That doesn’t mean it’s impossible, just that it’s complicated, and research is still being done to sharpen the theories at the edges.

However, I bring this up because Darwin does not explain the evolutionary mechanics behind eusociality, but his objection: is doing reformulate the way we should think about our friends, the exploding ants. Rather than worrying about their suicidal tendencies, we need to understand a simple fact: In evolutionary terms, a sterile worker is already dead. They are a resource to be spent by the breeding stock at the heart of the colony, not an autonomous resource.

When I was a kid I always felt guilty playing games like: starcraft or Age of Empires. I knew the best way to play them was to just build units so they could fight and die on my behalf, but I could never bring myself to be that ruthless, even to the little people on my computer screen. Ant queens have no such worries. They lay their eggs, they hatch their little minions, and they spend those minions for the greater good of the colony. And if that greater good requires them to blow themselves up in a smear of poisonous gunk, who cares? Not the queen. Thousands more where they came from.

Once you move from the individual level to the organizational level, the evolutionary behavior of these ants becomes clearer: they are replaceable parts of a whole, specially adapted for a specific task. Autothysis costs a colony resources, of course, but they are resources that can be replaced, a bit like the human body sacrificing white blood cells to fight infection. Thinking on this scale, with the colony as its own genetic unit, eusociality becomes even more fascinating.

Incidentally, the explosives workers are not the only specialists available for colobopsis ants. When fighting doesn’t work and when their venom squads fail, the ants sometimes have to retreat to their burrows. And they redirect rearguard action to a special type of soldier:

Yes, they fill the gaps with their faces. Very normal ants.

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