Why Do Ants Walk in Circles?

We’ve all probably stumbled on ants just kind of doing their thing before. Most of the time they’re just doing a little follow-the-leader thing, to and from a little crack in the sidewalk or something. But every now and then, we might run into ants just… walking in a circle. Forever. Well, not really forever, because they’ll walk in this circle until they die. So, what’s up with that? Why do ants just walk in circles like that?

Ant Communication

Before we talk about ants behaving weirdly, it’s probably a little important to talk about how ant society might work to begin with. Ant society is very much greater than the sum of its parts. You’re probably vaguely familiar with ant colonies, in the sense that they’re these really big basically-ant-cities with a bunch of worker ants and a big queen ant who lays a bunch of eggs (some ant species have multiple queens per colony). 

Ants are super specialized in their roles, forming a strict caste system. This extends to their physiology too, worker ants are all born sterile until another queen is needed. Workers of the Cephalotes and Carebara genera are born with big, flat heads. This allows them to use their heads as walls and plug entrances to their colonies as a means of warding off invaders. Ant warfare could be an entire series of in and of itself, honestly. 

You’re probably familiar with ant communication via pheromones. Ants basically leave trails behind when they venture out so others know to follow. Since ants don’t think critically, this keeps things simple. That’s not the only way ants can communicate, though. Sometimes, they throw up in each other’s mouths. This is called trophallaxis, and doesn’t seem very socially-distant. You might be familiar with this mostly in birds, which throw up in baby birds’ mouths as a form of feeding. Carpenter ants, though, use this as a means of communication. They have two stomachs for this reason. Sometimes, the vomiting is for food exchange, carpenter ants have been observed doing this when hungry workers venture back to the colony—or as a means of appeasing each other. But in line with the ant caste system, it’s also used to decide what roles ant larvae will have when they grow up. 

The Supercolony

We alluded to this earlier, but some ant species use multiple queens in a single colony. Sometimes, they’re all in the same little hole. But others, like the Argentine ant, take this to the next level. 

Argentine ant colonies, even when queen counts are at their seasonal low, are still roughly 10% queen ants. Each queen lays up to 60 eggs per day. These ants often send out their queens to new nests, making new colonies that are connected into one super-colony. With all of this in mind, you’re probably not surprised to hear that Argentine ants are ranked among the worst invasive species worldwide. One of the few checks against the Argentine ant is the war they are always waging against each other. Sometimes evolution takes its course, and minute changes in these separate-but-connected colonies eventually compound and the colonies begin to compete with each other instead of cooperate. Kind of like when a family member moves to another country for like 10 years and when you see them again they’re a totally different person. 

Now when we said super colony, we meant it. The largest Argentine ant colony stretches through the mediterranean, with sister locations in California, Japan, New Zealand, and Australia. 

The point we’re trying to make here is that, well one ants are kind of cool. But two, ant’s have to communicate on a very large scale. It’s kind of like the cells in your body. A single cell can’t really do all that much, but you put them all together and you have a human that thinks critically. Same with ants. No single ant is really intelligent enough to do all that much on its own, and really act based on signals. Signal A means do X, and signal B means do Y. 

Also, now you can talk about the giant intercontinental super ant colony. 

It’s a Feature

So, that thing where ants just walk around in circles until they die. This really results from ants losing track of whatever trail they were following. Without a pheromone trail to follow, the ants default to just following the one in front of them. Normally, this is an effective tool for self-organizing ant colonies—think about how often you’ve just copied the person next to you in a bid to go unnoticed. 

Unfortunately, when the ant in front of you also has no idea where to go (and you throw in a couple hundred of them), they end up just following each other all into a circle. All of this is something that can be recreated pretty easily in a lab. 

These spirals are called ant mills, or more dramatically: death spirals. The largest of which had a 1,200 foot circumference. That means its diameter was longer than an entire football field. 

See if you know where the most insects are, taxonomically, here.