Understanding Browntail Moths
If you live in Maine and enjoy the outdoors you likely know a little bit about browntail moth. Like many others you may have even developed a strong (or itchy) opinion about them in the past few years. With recent outbreaks, browntail moth has become an issue for both forest and human health in Maine. With the caterpillar’s toxic hairs causing rashes and even respiratory issues in humans and the caterpillar’s voracious appetite for hardwood tree leaves , many are searching for solutions.
At Hirundo Wildlife Refuge, we are fortunate to collaborate with the University of Maine Forest Entomology lab as they study the browntail moth, contributing valuable data to address their impact across the state. We hope to use this opportunity to share some insights about browntail moth with our community. January is the perfect time to dive into this discussion. Why? Browntail moth winter webs!
What Are Winter Webs?
In early fall, the newly-hatched browntail moth caterpillars construct communal silky webs around bundled hardwood leaves to overwinter in. The silk from the winter web provides protection from the elements and anchors their winter home to the tree branch. In the spring, the caterpillars will emerge from these cozy webs to feed on the new tree leaves. Identifying these webs is critical for managing the browntail moth population because it allows landowners to take action before the caterpillars become active and spread.
Winter webs are typically about as wide as a baseball or smaller and are often found in the upper canopy of oak, apple, cherry, and other deciduous trees. Their white, silky appearance can make them stand out against bare branches on a sunny day, making winter an ideal time to spot and remove them.
Why Winter Is the Best Time for Removal
During the winter the caterpillars in the webs are vulnerable as they are dormant at this time. Winter removals can significantly reduce the number of spring caterpillars in your area as winter webs can hold more than a couple hundred caterpillars each. This proactive approach minimizes the damage they can inflict on trees and reduces the risk of human exposure to their toxic hairs later in the year.
Removing winter webs involves clipping them from branches and then destroying and disposing of them one of two ways: soaking them in soapy water for several days or by burning them. This method is best for webs within your reach. Pole pruners are an excellent tool for removing browntail moth webs that are out of reach by hand. However, if the webs are still inaccessible even with pole pruners, that's okay—your safety is the most important thing. It is also essential to handle these webs with care. Anyone taking on the task of winter removals should do their research on proper removal and don protective clothing and gloves. Dormant caterpillars will have toxic hairs, but removing them while they are inside their winter webs significantly reduces the risk of exposure to those hairs...
For more information on identifying and removing winter webs you can check out this Maine Forest Service video!
(I unfortunately have first-hand experience from working in the browntail moth lab at the University of Maine in 2019 counting caterpillars in treated winter webs and despite my lab coat and goggles it turns out that ripping open the winter webs a few feet from your face in an enclosed area to dig around and handle the caterpillars generally leads to puffing miniscule hairs into the air and rashes on any exposed skin... It was fulfilling to be a part of the data collection and research, but when the position ended I can’t say I was too upset. This work is not for the faint of heart and I am very grateful for the work of the University of Maine Forest Entomology lab and others!)
History of Browntail Moth Outbreaks
It may surprise you to hear that this is not the first outbreak of browntail moth in New England. The species was accidentally introduced to Massachusetts in the late 1800s from Europe. Within 10 years they had spread across New England and into Canada. So why haven’t we really heard about them until this recent outbreak? Browntail moth populations were severely reduced due to removal and management efforts, leaving only small populations on Cape Cod and in the Casco Bay area of Maine by the 1970s. This is attributed to a combination of “insecticide spraying, biological controls, public action initiatives and changes in the landscape” (Groden et al.) It is extremely unlikely for us to achieve this exact combination again. The widespread general insecticides used were damaging to the environment (Lead Arsenate, DDT, etc.) and they killed insects indiscriminately, including native species and essential pollinators, and can cause health issues for other animals and humans as well. Public bounties were offered up to community members for climbing trees and collecting winter webs. With current awareness of safety and health issues involved in the widespread use of insecticides and the possible dangers in incentivising community members (including many children at the time) who may not have the right tools and protective equipment to climb trees and collect webs, new solutions are desired. Many are aiming to develop solutions that are both environmentally safer and less harmful to other species, humans, and their health, while remaining effective. Achieving this will require a deeper understanding of browntail moth itself.
Research at Hirundo
Hirundo Wildlife Refuge is one of many study sites that the University of Maine Forest Entomology lab is exploring, adding to the growing body of research on these invasive critters. As part of this research, they set up pheromone traps on-site this summer to monitor male moth populations. This winter, they will return to survey the refuge’s trees for winter webs to further their understanding of the moth's distribution and behavior. One of the lab’s goals is to see if adult moth and winter web counts can be used to predict browntail moth populations. If the populations can be monitored and caught before they balloon up again, then management could be done before they become a widespread problem. We at Hirundo are thrilled to be hosting researchers and sharing their findings with the community when possible.
What You Can Do!
If you are worried about browntail moth populations in your area there are a few ways you can get involved! Safe removal of winter webs from trees on your own property is one and now is the time to act (caterpillars will remain in the webs till the end of March or early April). Another way to help is educating others. Share this information with friends, neighbors, and family. The more winter webs removed the better! Additionally, supporting research and conservation efforts like those happening at Hirundo.
We’re excited to see the results of this ongoing research and will continue to share updates about this project. By working together, we can help protect Maine’s trees and communities from the impacts of browntail moth.
For more information on removals and safety we encourage you to explore the Maine Forest Service website: https://www.maine.gov/dacf/mfs/forest_health/invasive_threats/browntail_moth_info.htm#:~:text=The%20browntail%20moth%20is%20an,New%20Brunswick%20and%20Nova%20Scotia.
References:
Special thanks to graduate student Devin Rowe for the updates on the University of Maine Forest Entomology Lab’s browntail moth research!
Identify Browntail moth Winter nests: Insect & Disease Fact Sheets: Forest Health & Monitoring: Maine Forest Service: Maine DACF. (n.d.). https://www.maine.gov/dacf/mfs/forest_health/insects/browntail_moth_id_winter_nests.htm
Browntail Moth Caterpillar | Maine CDC | Department of Health and Human Services. (n.d.). https://www.maine.gov/dhhs/mecdc/infectious-disease/epi/vector-borne/browntail-moth/index.shtml
Browntail Moth (see photos below) - Home and Garden IPM from Cooperative Extension - University of Maine Cooperative Extension. (2024, December 10). Home and Garden IPM From Cooperative Extension. https://extension.umaine.edu/home-and-garden-ipm/fact-sheets/common-name-listing/brown-tail-moth/
Browntail Moths at UMaine: Researchers shed light on Maine’s ongoing battle - UMaine Research - University of Maine. (2023, October 12). UMaine Research. https://umaine.edu/research/2023/10/12/browntail-moths-at-umaine-researchers-shed-light-on-maines-ongoing-battle/
Groden, E., Karla Boyd, Hwang, H. W., Cole, B., & Mech, A. (2020). Browntail moth research at the University of Maine. https://sbe.umaine.edu/wp-content/uploads/sites/92/2021/04/Browntail_Moth_Report_FINAL_6-15-2020-V2.pdf
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