A bug’s life: Dead ants and snail shells in ant trash

Ants, like humans, have garbage. They dispose of their trash outside their nest in a dump called a midden, and the things they discard — seeds, rocks, dead nestmates — hold clues about their diet and social hierarchy.

Sometimes, this trash includes fragments of snail shells. Krings et al. wanted to uncover where these snail shells come from and why the ants discard them.

After identifying the many species of snail shells represented within the midden of a Messor wasmanni colony, the researchers studied the forces required to crush museum-quality specimens from the same species. They also conducted force experiments with mandibles from dead ants found in the midden and compared the two measurements to determine whether the fracture patterns in the shells from the midden were consistent with the ants’ mandibles’ failure resistance.

Snails represent a small part of M. wasmanni’s diet, but all the shells the researchers found in the midden were from juvenile snails. This pattern matched what they saw in their force measurements: The mandibles were capable of breaking juvenile shells but not thicker adult shells. Author Wencke Krings said this likely has to do with evolution.

“Of course, snails don’t want to be eaten,” Krings said. “So, we have a co-evolution between shell strength and mandible performance — a predator-prey interaction. It’s like an arms race.”

In analyzing the makeup of ant mandibles, the group found the mandibles get their strength from long chitin fiber bundles enriched with zinc. Though other insects incorporate different metals, zinc is unique to ants, and with more zinc come harder and stiffer mandibles.

“We have an idea of what forces chitin can withstand, and it is quite high for such a tiny structure,” Krings said.

By studying additional ant species in the future, the researchers hope to better understand the role of the chitin composite in the mandibles’ mechanical properties — and perhaps find more clues about why there are snail shells in ant trash.

Source: “Shell damage and mandible mechanics in the ant Messor wasmanni,” by Wencke Krings, Bernhard Hausdorf, and Stanislav N. Gorb, Biointerphases (2026). The article can be accessed at https://doi.org/10.1116/6.0005368 .

This paper is part of the Biomimetics of Biointerfaces Collection, learn more here .