Ash sawfly, Tethida cordigera . They are pale greenish white, with a darker green median stripe, black head and legs. Carbaryl or malathion, which are among the compounds registered for control of this pest in Connecticut, can be sprayed on foliage if damage becomes intolerable. Consult the label for dosage rates and safety precautions. Fall webworm , Hyphantria cunea.
Webworms damage the leaves of ash by both feeding and web building.
Webworms overwinter within cocoons located in protected places, such as crevices in bark or under debris and fences. Adult moths emerge in summer. Females lay white masses of 400-500 eggs on the undersides of the leaves. The caterpillars hatch in 10 days, and all from the same egg mass live together as a colony. They spin webs that enclose the leaves, usually at the end of a branch, to feed upon them.