Pavement Ants

The pavement ant, Tetramorium caespitum, is common in Indiana and an occasional indoor pest. Its mounds are often built in the cracks of pavement. The mounds generally form a perfect circle. How do the ants know to build the mound in a circle?

The simple answer is that they don’t know. Contrary to popular science fiction, ants do not communicate by telepathy and the workers do not take direct orders from their queen. There is no construction foreman to guide the ants and no blueprints. Ants and many other Hymenoptera respond to cues in their environment with a stereotype behavior that results in the production of complex structures.

The ant mound is the product of thousands of ant trips. As worker ants inside the nest enter an area that is expanding, the workers will pick up soil particles with their mandibles and head for the exit. Once outside the nest entrance, workers release the soil particle within several steps of the nest. A worker that has left the nest will move in a random direction. Ants are no more likely to go in one direction than another. When these random movements are averaged over thousands of ant trips, all 360 degrees of the compass are covered in relatively equal numbers.

Thus the ant mound is not round by design at all, even though it appears that the ants have a circle “in mind”. The circle is merely the product of thousands of ant deposits made completely at random.

Pavement Ant Mound

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
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