Browntail Moth Update #9: July 6, 2022

Late last week, we got our first reports of adult browntail moth (BTM) and have made more observations of adult emergence over the weekend. This marks the beginning of a shift in tactics to mitigate attracting moths to your dooryard by keeping unnecessary outdoor lights off until the beginning of August.

Image: Adult browntail moth resting on a wall. Note the large brown abdomen or “tail”.

Around the same time that browntail moths start showing up on lampposts, posts abound on social media encouraging the use of a light trap to “eradicate” BTM. We often get asked if light traps or bug zappers are effective at controlling adult moths, and the answer is a resounding no. Why?

• Bright lights will draw in more BTM dispersing from other areas.
• People who have tried this method report that they notice more BTM winter webs in their trees, particularly those around the lights, the following winter.
• Many parasitic flies and wasps that attack BTM are also drawn to light, reducing their impacts on browntail moth populations, not to mention other non-target effects.
• Females attracted by lights generally hang out on the host foliage nearby, with more males drawn directly to the light.

Unfortunately, the females are crucial in keeping the population levels high, so killing just the males won’t make a dent in the population, especially in heavily impacted areas. We recommend keeping unnecessary outside lights off between 9:00 PM and midnight until the beginning of August to avoid attracting more BTM to your yard.

Image: Adult moths attracted to an outdoor light.

Which one of these moths is not like the other? Many white moth species in the northeast are active around the same time as BTM. This simple chart can be used to differentiate lookalikes from the real deal. Please note that other species may also be confused for BTM.

People often ask if the adult moths have the same toxic hairs as the caterpillars. The answer is no. The hairs on the abdomens of the adult moths are not hollow and filled with the toxin, nor are they barbed. That being said, some people can experience irritation from exposure to the moths. Keep in mind that many moth species in their adult and larval forms have hairs that can cause a reaction in sensitive individuals.

Even though we are starting to see adults, both recently vacated and still inhabited pupal cocoons are still present. The coarse silk cocoons surrounding the pupae contain the last cast skin of the caterpillar, or caterpillars, and are full of toxic hairs. Many people become exposed to the hairs through encounters with the cocoons. Cocoons may be found on buildings, vehicles/ trailers, other outdoor equipment, plant stems, branches, and foliage. To prevent BTM from hitching a ride, check vehicles, trailers, and other materials for cocoons or adult moths before moving them.