The following very helpful information is from Tulle Frazer. She reported seeing Browntail moths laying eggs in late July.

“I was out on one of my several daily rounds to kill Japanese beetles today, but was sidetracked by a more bothersome insect. I killed about 30 adult Browntail moths that I found laying eggs. I believe they die when they are done laying and they are so involved that you can easily snip off the leaf they are laying on and they won’t fly away. I used rubber gloves because they do cover their eggs with their toxic brown hairs. It is best if you can hold onto the leaf petiole when you snip it off so that the moth and egg mass don’t fall to the ground. I had a yogurt container half-filled with soapy water. I dropped the leaf with moth and egg mass attached, put the lid on, and shook it occasionally to make sure all leaves were submerged.

I checked many species of trees and found them only on Rosacea…lots on our plum and crabapple, just two on a wild cherry tree, one on a rose bush, and one on our garbage can. Last fall all the nests we saw were high up in oak trees. The eggs they are laying now are too small to see if they are high up in the oaks. I would imagine they are there. It was satisfying to kill so many potential Browntails knowing that each female lays 200 – 400 eggs. I got a few new rashes in the process, but it was worth it.

Browntail moth laying eggs

To find them, look mainly on the underside of leaves if you have any Rosaceae trees that aren’t too tall. They were mostly at mid-height or higher in our fruit trees…none on the lowest branches. Once you have the search image you will likely also find brown egg masses of various sizes where the bright white female moth has already fallen off. On branches you can’t quite reach get a helper to bend the branch down to you.

The pupae develop into moths, which emerge from the cocoons in July. The moths have a wingspread of about 1 1/2 inches and are strongly attracted to light. Wings and midsection are pure white while the abdomen (rear part of the body) is brown with a conspicuous tuft of brown hairs at the tip.

After emerging, the females lay eggs in masses on the underside of leaves and cover the eggs with brown hairs from their bodies. Each female lays 200 to 400 eggs. The eggs hatch during August or early in September and the young larvae feed for a short time on the leaves before building their winter webs. This fall feeding does little damage to the trees.”