Browntail Moth Update #14: December 20, 2024
Throughout the winter season in Maine, browntail caterpillars are nestled inside of their winter webs that they created in late fall. These winter webs can be found on the tips of the branches of their host trees, typically oak, birch, cherry, crabapple, and other fruit and hardwood trees. Winter webs made by browntail caterpillars have a distinct white silk covering that protects them from the harsh Maine winters.
Now through March is the best time to go out and begin scouting for winter webs on your property. A sunny day makes for a good scouting day, as the white silk of the winter webs will shine back at you - a good indication of a browntail winter web. Sometimes, oak and hawthorn trees hold onto marcescent leaves, which are dead leaves that haven't yet fallen off the tree, which can be confused for browntail webs.
Browntail moth winter web on host shrub in Newport, ME.
- Maine Forest Service surveys cannot be exhaustive. The most important populations of browntail moth that may affect your daily life in the spring and summer may not be found by these surveys.
- Browntail moth experienced a drastic population reduction in 2024. That means aerial survey only highlighted scattered small areas of concern (see map below). Trace to moderate populations may be found throughout a large area of the state. Small numbers of webs can produce enough caterpillars to cause an itchy spring and summer.
- By recognizing webs in winter, you can respond to their presence and reduce impacts in spring and summer.
Aerial survey of defoliation from browntail moth in 2024. Hot spots of defoliation are noted in orange on this map.
Scouting for webs is an important first step in understanding browntail moth populations your backyard.
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Pick a sunny day for scouting to make the webs easier to spot.
- Prioritize trees that surround your home, driveway, porch, play areas, etc.
- Consider scouting for winter webs around your business, especially in areas where browntail moth caterpillars may emerge from winter webs in the spring and crawl onto vehicles (such as parking lots), or impact outdoor activities (such as picnic/break areas, near walkways and buildings, etc.)
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Stand with your back to the sun about 50-100ft away from the base of the trees.
- You may want to stand closer if scouting for webs on shorter, ornamental trees.
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Check for clumps of leaves at the tips of branches.
- On cloudy days, these leaves may appear brown or gray, but on sunny days, you'll be able to see a white silk covering on these leaves.
- Browntail winter webs will not be larger than the palm of your hand (roughly 3-5 inches long) and are typically narrow in width.
- Count (or estimate, if heavily infested) the browntail winter webs in each prioritized tree.
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Many browntail moth winter webs at the tips of tree branches in Augusta, ME.
In heavily infested trees (trees with 100+ winter webs), like the ones in the above photo, winter web removal may not be appropriate. Instead, pesticide applications may be considered if these trees are in a high-traffic areas such as your dooryard or the front of your business building.
So you scouted for browntail winter webs in your trees, now what?
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Remove webs that you can safely reach from the ground with an extendable pole pruner or pruning shears.
- Be sure to wear protective clothing (long sleeves, gloves, eye protection, etc.) when removing webs to prevent a rash from the residual caterpillar hairs.
- For webs that are inaccessible, or hazardous to remove (e.g. requires climbing, or webs are near power lines/traffic), consider hiring a professional to remove the webs.
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Collect clipped webs from the ground into a bucket.
- Browntail caterpillars are alive inside the winter webs. Leaving clipped webs on the ground will not eliminate the caterpillars and they will still emerge in the spring.
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Destroy the collected winter webs:
- Fill the bucket of winter webs with soapy water and let it soak for a few days to kill the caterpillars inside, OR
- Burn the webs by carefully placing the webs into a contained fire.
Still unsure about scouting for browntail winter webs in your trees?
An extendable pole pruner is being used to reach browntail winter webs in a crabapple tree in Orono, Maine.
Browntail mitigation should be focused in high-traffic areas for the most impactful relief. If there are populations you want to manage, hiring a licensed professional may be helpful.
Licensed pesticide applicators may have a limited schedule for timely spring pesticide treatments to reduce impacts from browntail caterpillars. If you have browntail winter webs in your trees that cannot be clipped, consider hiring a licensed pesticide applicator and get in contact with them in early winter. Pesticide applications should take effect before the end of May to be effective. Check out our list of applicators willing to treat browntail moth.
If you can't remove the browntail winter webs on your property, consider hiring a professional to assist with removal. Winter web removals should be completed before the end of March. Read our list of licensed arborists and FAA-certified drone operators who perform winter web removal throughout the state.
Browntail populations have declined in 2024. To understand the full extent of the reduction in browntail, we will continue our winter web survey starting in January 2025. These surveys are usually completed in March. After the data is reviewed, it will appear on our interactive browntail moth dashboard, which will give you a rough idea about what browntail is doing in your community.
We will recognize February 2025 as Browntail Moth Awareness Month, and will kick off the month with an educational webinar. We expect lower populations to result in unexpected encounters with browntail caterpillars in May and June. Help us reduce those surprises by supporting awareness of browntail moth before they emerge!
In the meantime, watch our browntail moth winter web removal video for extra guidance on scouting and removing winter webs in your community.
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