‘Ants are more complicated than people think’

To Clark Biology Professor Kaitlyn Mathis, ants are not only pests that sting or swarm your picnic — they also are industrious creatures that can benefit farmers and signal a healthy environment.

“Ants are more complicated than people think,” says Mathis, who has studied the behaviors of social insects for almost two decades. “I love how ants are this incredibly simple organism, but they can come together cooperatively in groups and do really complex things.”

Ants are farmers — some turn grass and leaves into fungi, which they store to eat later. Others “herd aphids like cattle,” she says. Honeypot ants’ workers collect liquid in their abdomens to feed the rest of the colony, including the queen.

Ants are warriors and builders. “They wage these complicated wars between themselves and other competitors,” Mathis says. “And they build really elaborate nest structures, all different kinds — in the ground, within hollowed-out acorns, or high up in the tree canopy.”

And ants are chemical engineers, emitting pheromones to attract mates, guide others to food, or set off alarms about invaders. “Ants can communicate pretty complicated messages to each other by using chemicals,” Mathis says.

Their fascinating, quirky behaviors led Mathis to study ants’ beneficial behaviors as a Ph.D. student in environmental science, policy, and management at University of California-Berkeley.

“I love how ants are this incredibly simple organism, but they can come together cooperatively in groups and do really complex things.”

— professor kaitlyn mathis

In Southern Mexico, when studying the Azteca ant, which is attacked by phorid flies that prevent the ants from foraging on pests within coffee plantations, she discovered a new beetle species. Phorid flies inject eggs into the aggressive Azteca ant, rendering it docile and helpless; the fly’s larva then emerges and eats the ant’s head.

Mathis observed a tiny beetle preying on the parasitized ant, consuming the phorid fly larva in the process. By conducting experiments with the beetles, along with healthy and parasitized ants, she discovered that the beetle was attracted to the injured ant’s alarm pheromone, but wouldn’t attack the healthy, aggressive worker ants twice its size. She concluded that “the Azteca ants are benefiting the coffee, and the beetles are helping keep the phorid flies from stopping that.”

“These results are the first, to our knowledge, to demonstrate a predator sharing cues with a parasitoid to gain access to an otherwise unavailable prey item,” according to Mathis and her collaborator. Their findings were published in Proceedings of the Royal Society B: Biological Sciences.

Mathis named the beetle Myrmedonota xipe for an Aztec deity “worshiped via human sacrifices … an apt metaphor for the beetles’ role in Azteca ant colonies,” she writes in The Conversation.

The research, she concludes, “shows that a complex web of interactions between many species of insects can provide important ecosystem services, like pest control, in agroecosystems.”

Can ants help farmers in New England?

At Clark, Mathis’ research — in which she always involves students, who often receive “first author” status on peer-reviewed journal articles — continues to unpack how undersized creatures can have oversized impacts on the food we grow and the places we call home.

In studying ants in “ecosystems that have been modified by humans” through agriculture or urbanization, she asks, “What does the ecology of these spaces look like? How does that impact the species interactions that you see there? And how might that affect how we manage those areas?”

Finally, “Can we leverage those species interactions to increase biodiversity, reduce pesticide usage, and make the world better?”

Maybe so. Humans have relied on ants as agricultural “workers” since 304 A.D., according to Mathis, the first recorded use of green tree ants by the Chinese to protect citrus crops from pests.

In the newly opened Experimental Plant Investigation Center (EPIC) attached to the Cathy ’83 and Marc ’81 Lasry Center for Bioscience, Mathis is overseeing Ph.D. candidate Joseph Nelsen’s investigation of how organic farmers in New England might leverage the interactions between striped cucumber beetle pests and ant protectors in cucurbits vegetable crops like cucumbers and zucchini. Nelsen’s dissertation research is funded by a U.S. Department of Agriculture Sustainable Agriculture Research and Education grant.

“Information gained from studies like mine … may be a useful tool for farmers dedicated to sustainably growing food.”

— PH.D. CANDIDATE JOSEPH NELSEN

Farmers often grow “companion” plants near crops that include specific traits that help them grow. Similarly, the Clark researchers are growing partridge pea wildflowers near the cucumber and zucchini plants. Both zucchini and partridge pea plants have extrafloral nectaries, “like little ant-sized dog bowls on the leaf or at the base of the leaf, and the ants drink out of them,” says Mathis, who is affiliated with Clark’s School of Climate, Environment, and Society, set to open in Fall 2025..

Many plants have evolved to include these extrafloral nectaries, attracting ants and other beneficial insects that remove pests like the striped cucumber beetle.

“We’re exploring whether we see plants locally that have these extrafloral nectaries and, if so, do we see beneficial insect presence increase?” Mathis explains. “How does that affect pest presence? How does that affect farmers’ crop yields? If you add companion plants that have extrafloral nectaries along the edges of crops, does that boost the presence of beneficial insects?”

Nelsen also is studying whether the ants’ chemical traces on the plants deter pests.

“Information gained from studies like mine will build on our understanding of the plant-protecting activities that abundant omnivorous insects like ants provide,” he says, “which may be a useful tool for farmers dedicated to sustainably growing food.”

Pests in California citrus orchards

When humans introduce new insect species, local ecosystems are disrupted, often leading to agricultural crop losses.

In a study of Southern California citrus groves, Mathis, her student Olivia Anastasio ’19, M.S. ’20, and Monique Rivera of the Entomology Department at University of California, Riverside, examined the interactions between native ants and two invasive insect pests — the Argentine ant and the Asian citrus psyllid it protects from insect “enemies.” A sap-sucking insect, the Asian citrus psyllid carries Huanglongbing, a lethal “greening” disease that threatens California’s $2 billion citrus industry.

Argentine ants were the most abundant ants in all 10 citrus orchards the researchers examined in Riverside and San Bernardino counties, according to their 2021 article published (with Anastasio as first author) in Agriculture, Ecosystems & Environment.

In crops where the Asian citrus psyllid is present, Argentine ants are more active and appear to have driven out many native ant species, according to the researchers. In addition, the ants were more active at citrus grove edges adjacent to other habitats or urban areas versus the grove’s interior.

The study could help farmers “reduce the amount of citrus psyllids by changing how much edge is present on their farms,” says Mathis, who earlier co-published a draft genome sequence of the Argentine ant in the Proceedings of the National Academy of Sciences.

Invasive ants in New England

Several years ago, Mathis and her students — Amelia Curry ’21, M.S. ’22, Nelsen, and Dale Stevens, Ph.D. ’22 — expanded their research to New England, collecting 61 ant species in 46 central Massachusetts sites, including farms, forests, and urban parks.

Since 1985, New England has lost nearly 865,000 acres of forest due to urbanization and agricultural use. This has led to a decline in ant biodiversity, which can “have serious ecological consequences, as these organisms provide many essential ecosystem services such as pollination, nutrient cycling, biological pest control and decomposition,” they explain in a 2024 article published in Insect Conservation and Diversity (with Curry as first author).

“Myrmica rubra is the most aggressive ant invasive species found in New England, with wide-reaching deleterious ecological impacts.”

— Amelia Curry ’21, M.S. ’22; PH.D. candidate JOSEPH Nelsen; Dale Stevens, Ph.D. ’22; and professor kaitlyn mathis

As in California, such changes can lead to a decrease in native ant species and an increase in non-native, more destructive ants.

“Overall, we found that land use type does have a significant effect on ant species richness, with farm habitats having a lower species richness than parks,” according to the researchers.

Of concern, they found Myrmica rubra, or European fire ant, in all areas, especially forests.

“Myrmica rubra is the most aggressive ant invasive species found in New England,” they say, “with wide-reaching deleterious ecological impacts on the invertebrate community, [and] is even capable of killing small mammals and negatively affecting the growth rates of ground-nesting birds.”

Are European fire ants spreading in the US?

Mathis now is working with biology Ph.D. student Daley O’Keefe on her dissertation research to better understand the spread of European fire antsin the United States.

“Humans bring in all of these invasives when we come to new places,” Mathis says, likely introducing Myrmica rubra to Boston from Europe in the early 1900s. Living mostly in cold areas, the ants also have been found in Canada and on the West Coast.

“It’s had a chance to establish,” she says, “but nobody has a sense of what it’s exact range is and how it’s impacting local species.”

O’Keefe seeks to determine how and where the insects have moved, what other insects can be found living and interacting with the European fire ants, and what kind of microbial community coexists within the ants.

“She’s really interested in thinking about how that microbial community might change based on where the ant is living,” Mathis explains, whether in forests or urban areas. O’Keefe is also looking at the population genetics of the ants, as well as their migration patterns into the U.S. and Canada, to help scientists, farmers, and others better predict where we can expect the European fire ants to move next.

How does urban heat affect biodiversity?

Human activity — such as rapid urbanization, which increases temperatures in and around cities — can disturb the beneficial ants that help maintain healthy ecosystems, according to Mathis.

In a first-of-its-kind study published last year in Ecology and Evolution, Mathis and her students — first author Brooke Harris ’21, M.S. ’22, and Stevens — explain the effects of higher temperatures on three types of cavity-dwelling ants (Aphaenogaster picea, Tapinoma sessile, and Temnothorax longispinosus), which “live in the hollowed cavities of fallen acorns, oak galls and twigs.”

Over two months, the scientists incubated and observed ants from urban and rural areas of Worcester at multiple temperatures in Mathis’ lab. They discovered that the three species reacted to temperature changes in different ways.

“Studying the ways in which cavity-dwelling ants adapt to these stressors can provide insight into the future of biodiversity and the ways in which conservation efforts should be applied to these areas of change,” the scientists say. Their study is the first “to address these metrics across multiple ant species from different habitats, providing a greater understanding into how intraspecific competition may respond to human development.”

As Mathis explains, “different species are evolving at different paces with different behaviors, so it’s a complicated web to untangle.

“If we’re going to live in an increasingly urban, increasingly warm world, what is this going to mean for these ant communities? How are they going to respond, and how universal are those responses?”

The fascinating world of acorn dwellers

Mathis’ research into ant behaviors continues in the EPIC lab, where she is observing the genus Temnothorax, the acorn-nesting ants. She keeps Tupperware containers full of hollowed-out acorns, each housing an entire colony, including the queen.

“If you’re walking through the forest, and you crack open an acorn, you might find an entire mini ant colony inside.”

— BIOLOGY PROFESSOR KAITLYN MATHIS

“If you’re walking through the forest, and you crack open an acorn, you might find an entire mini ant colony inside,” she says.

The ants rely on acorn weevils to “prepare” their homes. “The acorns fall from the trees and then acorn weevils burrow a hole in the acorn and put their larvae inside,” Mathis explains. “The larvae eat the contents of the acorn and leave before they become adults. That leaves this beautiful, hollowed-out acorn for the ants to occupy.”

Mathis is investigating how the acorn-nesting ants’ environment influences the dynamics within their colony. The ants generally live where there are oak trees, including in cities.

“In the summer, the acorn-nesting ants will branch out so they can expand their foraging range,” she says. “They will have multiple queens in what’s called a polydomous nesting structure with multiple acorns acting as satellite nests. Then in the winter, they’ll condense back into a single acorn for the winter to stay warm.”

Mathis doesn’t know where ants will lead her next, but by observing how they behave, interact with other organisms, and adapt to change, she’s always headed down a new, and potentially undiscovered, path.

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All photos by Steven King, University Photographer

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Explore climate and sustainability issues as a student at Clark