Building a Better Moth Trap

Describing her longtime interest in moths and butterflies, Mariana Abarca points to the fundamental role Lepidoptera play in sustaining life on Earth.

“What they do is turn plant tissue into protein in their bodies, and then they become food for other species,” says Abarca, assistant professor of biological sciences. “They are a very important link in the web.”

That link is now under threat. Climate shifts, pollution, and habitat loss have led to a global decline in insect populations. The falloff has been so steep that some scientists are calling it an “insect apocalypse.”

While there are reasons for concern, Abarca says, more research is needed to deepen scientific understanding of how insects are responding to changes in their environments.

“Knowing what is a normal amount of insects for any particular site is challenging,” she notes. “There are a million identified species of insects out of the four to seven million that exist, but only a few hundred have been monitored. Most places where there is monitoring are showing declines. What we don’t have is a baseline or widespread long-term data.”

Abarca is working to fill that gap by creating the first large-scale monitoring network of moths in both their larval and adult life stages. Supported by a grant from the National Science Foundation, her Moth Monitoring 2.0 project—a collaboration with researchers at the University of North Carolina Chapel Hill and the University of Florida—will collect data from a survey site at Smith’s MacLeish Field Station that will then be replicated at other insect-monitoring sites in the U.S. and Mexico.

The centerpiece of the effort is the Mothitor, an automated light-trap device that Abarca designed in collaboration with Smith faculty and students from engineering and computer science. About the size of a large briefcase, the Mothitor takes photographs of moths as they connect with a lighted landing surface. A computerized data visualization system then identifies the types and number of insects at the site. 

In a recent interview in her office overlooking Paradise Pond, Abarca shared some details about her project.

How has the Mothitor evolved since it was first designed in 2022?
“It’s been continual improvement, working with Smith engineering and computer science students and the Center for Design and Fabrication. The first version involved a lot of Tupperware containers [for parts]. The newest version takes better pictures. The devices are expensive—about $2,000 each. And you need to know how to code in order to use them. As part of the Moth Monitoring 2.0 project, we developed a more user-friendly and affordable version: a hybrid between the Mothitor, which we designed, and the Mothbox, an open-source design developed by Digital Naturalism Labs in Panama. One of the key improvements is an app so people can use the device with their phones. We made eight of these new automated light traps to test this summer—one here at MacLeish and the rest at partner sites in Florida, New York, North Carolina, Vermont, Virginia, and Wisconsin. Next year’s goal is to make 20 more to cover more sites in the eastern U.S.”  

How does the monitoring system work?
“People think that moths fly into the light, but actually they turn their backs to it. That’s when they get trapped and other animals learn to go to the light and catch them there. Smith engineering students designed the Mothitor to use black light to attract night-flying insects to a landing surface, then take pictures using a camera connected to an electronic controller encased in a waterproof box. A computer science student developed an AI model that identifies insects in the photos.

“For the larval stage monitoring, we’re working with the [national] Caterpillars Count! citizen science project to set up monitoring stations at their counting sites. We’re also building a ‘frassatorium,’ which is a national repository for caterpillar frass [poop]. Frass contains the genetic material of both the caterpillar that produced it and the plants it ingested, so it’s a rich source of information about the biodiversity of caterpillars in an area and their interactions with plants.” 

How has being at Smith helped shape your project?
“What’s unique about Smith, and what makes this project possible, is that we care so much about education and interdisciplinary collaboration. This project enriches teaching in multiple disciplines, and meeting those educational goals means we can keep the monitoring work going. My Quantitative Ecology students from 2024 contributed to the design of a summer experiment using the Mothitor, then students enrolled in the 2026 iteration of the course participated in data analysis. Students in computer science and statistics and data sciences are also doing class assignments with our monitoring data. This project is only possible through the collaboration with my colleagues in those departments.” 

What do you hope will be the impact of the moth monitoring?
“This project has funding for three years, but we hope we can keep it going even longer. Insect populations experience natural peaks and declines, so we need decades of monitoring data to know their population dynamics. All of the data will be available to researchers who are trying to understand what is impacting insect declines. We are also preparing a manuscript on best practices for moth monitoring, as automated traps are increasing in popularity and more people are deploying them. What I really want to do is foster insect appreciation. They are so important to the health of our environment, but there’s a whole industry that just wants to kill them.” 

Along those lines, we have to ask: moths eat plant protein, so why do they go after our wool sweaters?
“Most moths eat plants, but there are some species that eat other things such as hoofs, horns, and bird feathers. They can feed on that because they feed on keratin, which is also present in wool and silk and other household items. The species of moths that feed on leaves would never eat clothes—keratin-feeding species are a minority among moths. Fun fact: there are some moths that eat the larvae of paper wasps!”