Amber-colored ants, Wasmannia auropunctata, or electric ants, nest inside a coffee berry that had been previously occupied by coffee berry borers. Credit: Jonathan R. Morris

A tiny coffee pest may be building the perfect hideout for its own predators.

Coffee berry borers tunnel deep into coffee fruit, where they feed and reproduce beyond the reach of many predators. But after tiny ants force the beetles out, some species appear to claim the abandoned chambers as nurseries for their young.

Jonathan “Jonno” Morris first noticed the behavior while studying coffee plants in Chiapas, Mexico. His observations provide the first documented evidence that small ants can reproduce inside spaces originally carved by coffee berry borers. The discovery reveals an unexpected ecological feedback: the pest creates shelter that may ultimately strengthen populations of the ants that attack it.

Coffee berry borers spend most of their lives protected inside coffee fruit. Females drill through the outer surface and create galleries where they lay eggs. Their developing offspring then feed on the seed, the part of the fruit that eventually becomes a coffee bean. Because much of this damage happens inside the fruit, the insects are notoriously difficult to control.

How Ants Hunt Coffee Berry Borers

Larger ants can catch adult borers before they enter the fruit, while smaller species are able to squeeze into the beetles’ tunnels and prey on adults, eggs, larvae, and pupae. Morris found that the relationship does not always end when the pest is removed.

An ant approaches an opening in a coffee berry created by a coffee berry borer beetle, while another ant is already inside. Credit: Jonathan R. Morris

Some ants cleaned out the damaged chambers, widened the beetles’ entrances, and moved their own developing young inside. Morris recorded seven ant species occupying previously infested fruit, with five showing evidence of reproduction. They included the electric ant, Wasmannia auropunctata, as well as species of Pseudomyrmex, Nesomyrmex, and Procryptocerus.

“In terms of pest control, this is primarily a good thing because it’s benefiting the ants in terms of their populations and fitness. The ants gain this reproductive benefit that’s originally created by the coffee pest. And this might actually help to maintain more diverse ant communities directly on the coffee plants,” Morris said.

By nesting inside coffee fruit, the ants remain close to places where new infestations are likely to appear. That proximity could increase their chances of encountering borers moving into nearby fruit, potentially extending their role as natural pest controllers. The study does not establish how much the behavior reduces crop damage, but it identifies a possible mechanism that could help sustain beneficial ant populations on coffee plants.

An Accidental Discovery in Mexico

The discovery began almost by accident in 2016. Morris was working on another project at a research station established by University of Michigan ecologists Ivette Perfecto and John Vandermeer on an organic, shaded coffee farm in Chiapas. While opening green coffee fruit that had been attacked by borers, he repeatedly found ants living inside.

“I had all these ants in vials that I had found nesting in coffee fruits and told myself, ‘Maybe I’ll do something with this at some point,'” Morris said. “Then, years later, I got to thinking about it, and, as far as I know, this is the first time anyone’s documented or reported the ants taking advantage of the niche construction by the berry borer and using it to reproduce themselves.”

Ants foster their brood in a coffee berry that was once home to a coffee pest. Credit: Jonathan R. Morris

Morris returned to the farm with research technicians in 2025 to collect more evidence and capture the first photographs of the behavior. The findings were published in The Scientific Naturalist section of the journal Ecology.

When One Species Builds for Another

Ecologists describe the interaction as a form of indirect niche construction. An organism changes its surroundings, and another species later benefits from the altered habitat. In this case, the borer creates a protected chamber, the ants evict or consume the beetle, and the structure becomes a nesting site for the pest’s natural enemies.

The finding also complicates the idea that every pest must be completely eliminated for an ecosystem to function well. Very small borer populations might provide both prey and nesting space for ants that help suppress larger outbreaks.

Morris said the discovery is also a reminder that valuable scientific insights can begin with simple observations in the field.

“Right now, there’s an emphasis from funders on AI and big data, but before people had all these fancy tools, they were going out into nature and making observations and discovering patterns. Think about Charles Darwin and Alexander von Humboldt,” he said. “But if it wasn’t for having funding for basic science and doing these types of observations, I wouldn’t be sitting here talking about them.”

Reference: “Indirect niche construction: A coffee pest facilitates its own ant natural enemies” by Jonathan R. Morris, 24 July 2026, Ecology.
DOI: 10.1002/ecy.70463

This work was supported by UNAM through its Postdoctoral Scholarship Program.

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