BTM Update #3- May 5, 2023
The cool, rainy weather we’ve experienced this past week has delayed browntail moth host development at most sites, although they are slowly pushing out leaves and flower buds. At the sites we visited during the rain, browntail caterpillars were nestled inside their soaked webs; however, there were some that seemed to be using their web as an umbrella. Caterpillar feeding activity has caused some bud and leaf damage but cool, wet weather has prevented it from being severe. As we get warmer, sunny weather, have no doubt that these very hungry caterpillars will make up for lost time. Regular periods of rain during the weeks when the caterpillars are active are the most beneficial from the standpoint of caterpillar disease development (and plant growth, too).
In the coming weeks, we will be on the lookout for disease outbreaks caused by the pathogens that attack browntail and we welcome your reports as well.
Browntail caterpillars shelter underneath their web in Ellsworth, ME; note the “gauzy” silk indicative of spring activity.
As mentioned last week, browntail caterpillars have begun producing silk and expanding their winter webs. There is a native look-alike, called eastern tent caterpillar, that can be confused for browntail moth webs at this stage in development. Two key differences between the webs of these species are the size and position on the host plant. The silken nests of our native eastern tent caterpillars start small but can grow quite large, reaching around the size of a football and are attached to the tree where the branches meet the trunk or where they come together. The silk that comprises eastern tent caterpillar webs is also denser, creating a white screen that is hard to see through. Additionally, eastern tent caterpillars lack the two characteristic orange spots on the tail end of the caterpillar.
One place eastern tent caterpillars create their webs is at the base of a branch where the branch meets the trunk, like in this photo.
Another place eastern tent caterpillar webs make their webs is further out on a branch where the twigs meet the branch. Note for both eastern tent caterpillar web photos, there is dense white silk with no dead leaves incorporated into the webs.
Non-native browntail winter webs are the size of your palm or smaller, are constructed in late summer and early fall on the tips of the branches and are comprised of silk that also incorporates the leaves on the branch tips. As the caterpillars become active in the spring, they travel in and out of the web, and the web can become surrounded by gauzy silk similar in texture to that made by the eastern tent caterpillar. Browntail moth caterpillars are dark brown and have two orange spots towards the rear of their bodies. As the caterpillars molt, they develop white stripes due to white tufts of hair on each segment.
Browntail moth winter web with “gauzy” white silk characteristic of spring activity, Unity, ME.
Where is Browntail Moth in Maine?
Maine Forest Service conducts surveys for browntail moth from small planes and from moving trucks. These are broad-scale surveys that do not completely cover the impacted area. You can get a broad idea of where browntail moth is in Maine from our interactive map, just updated with 2023 winter web surveys. To understand what browntail moth is up to in a specific area take a look at host plants for webs and signs of caterpillar activity.
Browntail Moth Mitigation Fund - Update
The Request for Applications (RFA) for the Browntail Moth Mitigation Fund is open through May 16. The fund was established to provide support to government entities or non-profit organizations in areas with significant browntail populations to reduce impacts from browntail moth. Only applications from government entities or non-profit organizations will be considered; funding is not available for individuals. The Division of Procurement Services Grant RFP/RFA page will have updates as soon as they are available. We will also include information in these bulletins.
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