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High-speed video solves how Florida ants furnish their nests with their enemies’ bodies

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Florida ant

Formica archboldi next to the remains of trap-jaw ants.
Formica archboldi next to the remains of trap-jaw ants.
Photo by Adrian Smith

The nests of Florida ants called Formica archboldi are adorned with the carcasses of their enemies — namely, the heads of other species known as trap-jaw ants. How Formica archboldi acquire these gruesome home accessories has perplexed scientists since the 1950s. But now, thanks to high-speed and time lapse videos, we have a better picture of this bizarre behavior.

The study has been long in the making for Adrian Smith, the head of the Evolutionary Biology & Behavior Lab at the North Carolina Museum of Natural Sciences and a professor at North Carolina State University. Like these ants, Smith, too, is from Florida — and he was drawn in by the Formica ants fondness for that abattoir ambiance. “We knew that little tidbit of natural history information,” he says. “There had to be some cool biology happening behind it that was waiting to be described.” So he set up colonies of Formica ants in his lab, brought in some trap-jaw ants, and used high-speed and time-lapse videos to watch what happened.

First, the Formica ants squirt the trap-jaw ants with a stream of formic acid that stuns them. Then, they pull the trap jaw ants apart. The Formica ants might also snack on the bodies, although that part is still up for debate. What’s even weirder is that these particular Formica ants and two different species of trap-jaw ants mimic each others’ smells, according to a study recently published in the journal Insectes Sociaux. That implies some sort of longstanding link between the species, but exactly what sort of link is still a mystery.

The Verge spoke with Smith about watching ants dismember other ants, and what that can teach us about the world.

This interview has been lightly edited for clarity.

Are Formica archboldi the most metal ants ever?

They’re one of the most badass ants I know of, that’s why I wanted to study them — they decorate their nests with skulls. A lot of other ants do cool things, but these are special to me because they’re from Florida, and I’m from Florida. Weird shit happens in Florida. This is another example of that.

How’d you start studying them?

I actually worked on this when I was like 20 years old and an undergrad in college at Florida State. The Formica ant is a pretty common type of ant. They’re around sidewalks and all across the US. In this area of Florida, you dig into the nest and you find body parts of the trap-jaw ant, which is this really awesome ant that has a spring-loaded mandible it can slam shut at over 100 miles per hour to capture prey. It’s got a pretty potent sting, it will capture things in its mandibles, and inject a venom that paralyze other insects and bring them back to the nest to feed to to their young. It’s pretty well defended: it’s known as a predator, not as prey.

So since the late 1950s, it was known that these Formica nests are filled with body parts of these trap-jaw ants, particularly their heads, for some weird reason. But no one had really studied it since the ‘50s. There’s basically no papers on that particular ant species. So I worked on it a little it when I was an undergrad and then a few years ago I started going back to Florida and working on it again, trying to figure out what was going on.

So you had an artificial nest of the Formica ants in the lab, and then you brought in trap-jaw ants to watch what would happen. But how did you actually observe what was going on?

I used two different video techniques to observe it. I used super high-speed video [with a Phantom Miro LC320s camera and a Vision Optics Laowa ultra-macro lens.]. So I filmed these ants’ interactions at 600 to 800 frames per second, and got a super slo-mo detailed look at what their attack strategies are. And on the total opposite end of that, I would do time-lapse video observations over like 20 to 24 hours to see what the ants were doing inside of the nest to the trap-jaw ants they collected and brought in after the trap-jaw ants were killed.

[Using these two methods] is something that I ended up having to do a lot when studying ants, because a lot of what they do happens at time scales that are way different from what we perceive. A lot of instantaneous insect behaviors are super, super fast. It just looks like a blur of motion, you can’t see anything. And then on the other side of that, a lot of the things they do as a collective happen over longer timescales that you can’t just sit down and watch. You have to condense all that action into a different time interval to see what they’re doing collectively as a group.

What did you discover?

When the Formica ants attack, the high-speed video would show these really quick bursts of formic acid being sprayed from their abdomens and splattering on the trap-jaw ants. That would instantaneously debilitate the trap-jaw ants — they can’t stand up or walk after that. Then, on the time lapse, you could see the Formica ants pull in a trap-jaw ant from where they get their food and bring it into the nest. And they’d start licking it, biting it, moving it around on the ground like they would with food. And then all of a sudden, 18 hours later, you’d see the head start to pop off of the trap-jaw ant. They would pull it apart, and start to dismember it. That’s something you can only see if you’re observing the thing for hours and hours. And that was cool because that’s basically replicating in the lab what was known in the field from those reports from 60 years ago: that there’s a bunch of decapitated trap-jaw ant heads floating around in nests. When you look at it on time-lapse in the lab, you can actually see that happen.

Why are the Formica ants doing this to the trap-jaw ants, do we know?

Short answer is no, but I have a lot of guesses. I think they’re somehow feeding off of them, because the trap-jaw ant body parts are hollowed out in the nest. You find some abdomens that are cracked open and totally empty. And then the surprising finding was that the [Formica] ants also chemically mimic the trap-jaw species. Usually when you see this type of mimicry, the ants are disguising themselves as something, so that’s probably what’s happening here — although I’m just now starting to research all the ways they might be disguising themselves with these chemicals, because I haven’t found any direct evidence for it yet.

What can these ants tell us about the world at large?

This kind of research is like telling the story of stuff you’d never assume has a story, and you’d never assume has things you could appreciate about it. These are small ants that don’t look like anything. They don’t look like big cool ants. They just look like “oh, it’s just another ant, it just does ant stuff.” But you’d never know that underneath this tiny hole in the ground, that there’s this nest full of basically the bones of other ant species, and that this ant is really good at spraying and taking down some of the fiercest ants that are in its ecosystem. So this type of descriptive natural history work it’s putting names and stories to things that are nameless and unknown.