Coffee Berry Borers’ Tunnels Serve as Ant Nurseries, Study Finds

Seven ant species have been observed reproducing inside tunnels originally carved by coffee berry borers in green coffee fruit, according to a study published 24 July 2026 in Ecology. The findings, based on fieldwork conducted in Chiapas, Mexico, represent the first documented case of ants using borer-excavated chambers as nurseries.

How the discovery unfolded

The observation began in 2016 when Jonathan “Jonno” Morris opened infested coffee fruit at a research station operated by University of Michigan ecologists Ivette Perfecto and John Vandermeer on an organic, shaded coffee farm. He repeatedly found ants living inside damaged fruit. “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 recalled. Years later, he returned to the site in 2025 with research technicians to collect additional specimens and capture the first photographs of the behavior.

Ants repurpose borer galleries

Coffee berry borers spend most of their lives inside coffee fruit. Females drill through the outer surface and construct internal galleries where they lay eggs; offspring then feed on the seed—the future coffee bean. Because this activity occurs entirely within the fruit, control remains difficult. Larger ants intercept adult borers before entry, while smaller species enter the tunnels to prey on adults, eggs, larvae, and pupae. Morris found that after evicting or consuming the beetles, some ants cleaned out the chambers, widened the entrances, and relocated their own developing young into the spaces. Five of the seven ant species observed—including Wasmannia auropunctata, Pseudomyrmex, Nesomyrmex, and Procryptocerus—showed evidence of reproduction inside the galleries.

Ecological implications of indirect niche construction

The interaction is classified as indirect niche construction: one species alters its environment, and another benefits from the resulting structure. Here, the borer creates protected chambers; ants remove or consume the pest; and the abandoned galleries become nesting sites for the ants’ offspring. This dynamic may strengthen ant populations directly on coffee plants and support greater ant diversity. By remaining close to fruit likely to be newly infested, the ants increase their chances of encountering incoming borers—potentially extending their role as natural pest controllers. The study does not quantify reductions in crop damage but identifies a mechanism that could help sustain beneficial ant communities.

Broader scientific context

“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. He noted that the finding challenges assumptions about pest eradication, suggesting very small borer populations might simultaneously serve as prey and provide nesting space for ants that suppress larger outbreaks. Morris also emphasized the value of basic field observation: “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.”

The paper, titled “Indirect niche construction: A coffee pest facilitates its own ant natural enemies,” appears in The Scientific Naturalist section of Ecology. It was supported by UNAM through its Postdoctoral Scholarship Program. DOI: 10.1002/ecy.70463.