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Ask Dr. Universe: Why do ants build mounds?

An ant and an aphid on a leaf. The two species are an example of mutualism, with both benefiting from the relationship.  (Shutterstock)
An ant and an aphid on a leaf. The two species are an example of mutualism, with both benefiting from the relationship. (Shutterstock)
Washington State University

Washington State University

Dr. Universe: Why do ants build mounds? – Isabelle, 4, Eagan, Minnesota

Dear Isabelle,

Ants build mounds in all shapes and sizes. Beneath those piles of dirt, ants are building their underground homes.

That’s what I my friend Rob Clark, an entomologist who studies bugs on plants. His job is to figure out if bugs make a plant sick or help the plant grow.

He told me ants are one of the most diverse insect families. Scientists know about nearly 13,000 species – and each ant species makes a different kind of nest.

Carpenter ants might make their nests in dead wood. Acorn ants make their nests in small twigs and acorns.

Then there are ants that create massive underground mazes that are like cities just for ants.

Ants are pretty good at digging underground tunnels with their little jaw-like mouth parts, too.

“The workers use their mandible to carry the dirt and make space for the queen ant and the larvae,” Clark said. The larvae are their babies who will grow into workers.

Some ants, like harvester ants, will dig nests up to 10 feet deep. While some ants make hills with the dirt they dig out, other ants make mounds they’ll actually live inside.

Thatch ants can make mounds that are up to 4 feet tall. The ants move around a lot of soil and bits of plants to shape their home. They like to build the mounds in a sunny spot, Clark said.

Ants don’t like the cold. The babies need a warm environment, and so do the workers.

Clark told me he actually saw one of these mounds while he was out in the field and thinking about your question. There were a lot of busy ants crawling around the outside and inside of it.

It turns out almost all ant nests start out with a young queen who has never had a colony before.

The queen excavates a small hole in the ground and picks up the soil with her mandibles. She will lay a few eggs, and the ants that hatch will become workers.

“As she lays more eggs and more workers grow up, they have to expand the size of their house,” Clark said.

While ants can take care of the house, they also can help with jobs like farming aphids, another little insect.

Aphids have sugary poop, called honeydew, that comes from the sap they eat. Ants eat honeydew and protect the aphids from other predators, much like a shepherd tending to a flock of sheep. It’s all part of something called mutualism, which means two living things helping out each other.

Now you know ants on our planet make different kinds of nests, but they do it for similar reasons. They need to create a safe place for their colony to eat, work and live.

A single colony can contain thousands of ants, and they all help one another survive.

Next time you see an ant hill, think about all the ants that made it and that there is a whole little world beneath it.

Sincerely,

Dr. Universe

Ask Dr. Universe is a project from Washington State University. Submit a question at askdruniverse.wsu.edu.

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