Harris Center turns local monarch sightings into data for broader research

PETERBOROUGH — Community members will have a chance to search milkweed leaves for monarch eggs and caterpillars Friday as part of a local monitoring effort contributing to research on the butterfly's population across North America. The Harris Center for Conservation Education will host "Monitoring for Monarchs" Aug. 21 from 9 to 10:30 a.m. in Peterborough. Staff ecologists Nate Marchessault and Brett Amy Thelen will guide participants through a Harris Center-conserved milkweed patch in search of monarch eggs, caterpillars and adult butterflies. No previous experience is required. "Participants can expect to use their careful observation skills to search for monarch eggs, larvae, and adults," Marchessault said. "This survey gives us the opportunity to slow down while we observe each individual milkweed leaf for eggs and caterpillars." Marchessault said participants will record the number of monarchs they encounter at each stage of the butterfly's life cycle. Monarchs may be the focus, but they are unlikely to be the only insect participants encounter. "Along the way, we're sure to have lots of other interesting finds like crab spiders, milkweed beetles, and milkweed tussock moths," he said. The information collected will contribute to the Monarch Larva Monitoring Project, a community science program of the Monarch Joint Venture that tracks monarch eggs, larvae and milkweed across North America. The project was developed by University of Minnesota researchers in 1997 to establish long-term data on larval monarch populations and milkweed habitat. "Monitoring for monarch eggs, caterpillars, and adults is important because it gives a sense of monarch abundance and reproduction in any given year, and over time can inform broad population trends," Marchessault said. Peterborough represents one small piece of that larger monitoring network. "The Peterborough site is just one of thousands of sites monitored through the Monarch Larva Monitoring Project throughout North America," Marchessault said. "By looking at hundreds of thousands of milkweed plants each year, the project provides quantitative data on observed population trends, which are openly available for volunteers or researchers to use." The monitoring has also allowed Harris Center staff to observe changes at the Peterborough site itself. Marchessault said the number of monarchs found there has declined alongside changes in the field's vegetation. "At our particular site in Peterborough, we have observed a decrease in the number of monarch adults, eggs, and caterpillars we've observed as the density of milkweed has decreased in the field," he said. "We've also seen an overall shift toward grasses replacing many of the pollinator plant species." Those local observations come amid broader concerns about monarch populations. Marchessault said trends in the Monadnock Region reflect a significant decline in the larger monarch population during the past three decades. "The biggest challenges monarchs face locally are loss or disturbance of habitat, pesticide use, and climate-driven irregular weather patterns due to shifting climate," he said. Community monitoring provides researchers with observations from numerous locations over extended periods. The MLMP encourages volunteers to receive training, monitor sites and submit observations through its data portal, allowing members of the public to contribute directly to the project's long-term dataset. Friday's event is free, but space is limited and registration is required. Participants should come prepared for sun, ticks and other biting insects. The exact meeting location in Peterborough will be provided to registered participants before the event. For more information, visit harriscenter.org/events/monitoring-for-monarchs-august-2026.