While scouting our trees for pecan nut casebearer we have discovered a few new colonies of fall webworm (photo at right). This is the first of two generations that will make an appearance during the growing season. A second generation will hit in mid-August.
Fall webworm caterpillars always appear in a large group and surround themselves in white webbing. The spinning of the web starts immediately after egg hatch. In the photo at right, a recently hatched webworm colony has eaten all the green tissue from the terminal leaflet and covered that leaflet in webbing. These insects web over the area in which they are feeding to protect themselves from potential predators and parasites. As the larvae grow in size, the amount of leaves needed to support the colony increases and the size of the web grows.
Female webworm moths lay their eggs on the underside of pecan leaves. The dime-sized egg masses are covered with white, fluffy scales deposited by the female to confuse egg parasites. In the photo at right, I've turned over the leaf pictured above so you can see the remnants of the eggs mass. At the tip of the brown leaflet the white fuzzy stuff left behind after the eggs have hatched.
At this time, it it two early to tell if we'll see an outbreak of these insects this summer. We will need to keep watching.