Recently I drove up to northern Vermont to see some friends who had just cut down a dead Elm. The butt log was spalted and they wanted me to check it out. They also pointed out some bug- damaged backyard Sugar Maples and asked if I knew what was discoloring and "folding up" or "curling" the leaves. I had no idea so I gave my cusomary reply, "Nope…but I'll try to look it up."
The Maple Trumpet Skeletonizer (Epinotia aceriella (Clemens)) feeds on mostly Sugar Maples but also likes Red Maple and occasionally Oaks and Beech. It is a moth which can be found as far North as Ontario to New Brunswick, Canada / South to North Carolina / and West to Michigan. Its larva eats the tissue between the larger leaf veins on the underside of the leaf. It spins a silken web and then folds the leaf. Inside the fold it constructs a "trumpet" shaped tube where it is safe to feed and to "skeletonize" the area beneath the web.
There can be more than one larva (and consequently more than one "trumpet") on the same leaf. The larva can be found from early July through early October and are pale yellowish green with a yellowish head. They drop to the ground to construct cocoons between two fallen leaves.
Like the fall webworm, its damage is more unsightly than life threatening because it happens so late in the growing season. If you have favorite trees that are infested, it helps to rake up the leaves and either compost or burn them.