Acromyrmex versicolor – Desert Leafcutter Ants

Acromyrmex versicolor worker and mesquite leaflets

It’s funny. For the first four or five years that I lived in Arizona, I had no clue that we had Leafcutter Ants.

Then, after seeing the first nest, it was as if they were everywhere. Come to find out, they are pretty common – and I think that they are also one of the most enjoyable ants to watch.

Desert Leafcutter ants – Acromyrmex versicolor –  are very, very cool. They often form long columns of ants entering and leaving the nests, with the ants carrying strangely shaped and colored parasols of vegetation.  Sometimes you can’t even see the ants, but you can see the fragments of twigs, leaves and flowers making their way to the nest seemingly on their own It’s like watching a confetti marching.

The ants don’t eat the leaves and twigs that they bring back to the nest themselves, though. Rather, they feed the leaves to a garden of fungi that the ants grow inside of their nests. The ants eat the fungus. It’s agriculture.

The ant nests  seem most common in sandy soil, either in desert washes or underneath shady trees. The nests are distinctive – they look like cartoon drawings of volcanoes. It’s common to find a number of these nest mounds very near to each other. I’m not sure if the these mounds are all entrances into the same nest, or if they are separate nests. I suspect that they are usually separate entrances to the same nest.

Acromyrmex versicolor nest mound in a sandy wash, with hat for scale. If you look carefully, you can see the workers inside the ‘volcano cone’ of the nest mound.
Series of Acromyrmex versicolor nest mounds. I suspect that these are all entrances to the same nest – but I do not know that for sure.
Small Acromyrmex versicolor nest mound

The ants either collect leaves, twigs and flowers off of the ground, or they will climb into the plants and use their jaws to snip off vegetation.

Acromyrmex versicolor major worker
Frontal view of Acromyrmex versicolor worker. The object projecting forward from between her mandibles is a piece of vegetation she was chewing.
Acromyrmex versicolor worker excavating dirt at the nest entrance
Acromyrmex versicolor worker excavating dirt at the nest entrance
The size of Acromyrmex versicolor varies within a nest. Here’s a minim, one of the smallest of the workers, surrounded by her larger sisters in a foraging column.
The size of Acromyrmex versicolor varies within a nest. Here’s a major worker, surrounded by her smaller sisters.

An interesting thing about a related South American species, Acromyrmex echinatior. Its exoskeleton incorporates “high magnesium calcite” crystals. These crystals toughen the ants’ exoskeleton, making them more resistant to the bites of other ants. Almost as if the ants have a suite of armour that’s reinforced with mineral crystals.

I would not be at all surprised to hear that Acromyrmex versicolor has something similar.

Acromyrmex versicolor worker cutting stem. They are able to cut pretty tough/fibrous vegetation, as in this case.
Acromyrmex versicolor worker and mesquite leaf
Acromyrmex versicolor carrying leaflets back to the nest. Note that this is not a living leaf.
Acromyrmex versicolor worker and leaflet. As you can see, the ants don’t always collect fresh, green leaves.

In spite of their spiny, fierce-some appearance, these ants are absolutely delightful. They move pretty slowly and deliberately are big enough to see easily, and usually have very sweet dispositions.

And best of all, they don’t sting.

Sources:
Li, H., Sun, CY., Fang, Y. et al. Biomineral armor in leaf-cutter ants. Nat Commun 11, 5792 (2020). https://doi.org/10.1038/s41467-020-19566-3

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