The elm spanworm is a native insect which is widely distributed over the eastern half of the United States and Canada from Nova Scotia south to Georgia and west to Colorado. The most widespread outbreak on record occurred during the period 1954-1963 when over one million acres of hardwood forests were defoliated in the mountains of western North Carolina, eastern Tennessee and northern Georgia. The elm spanworm feeds upon hickories and a variety of hardwoods; white oak, chestnut oak, and northern red oak are the species most heavily defoliated in the Appalachians. Repeated defoliation causes growth loss, reduces mast crops, and will eventually kill the tree.
Sixth instar elm spanworm larva.
Eggs are laid in masses of 12 to 200 on the undersides of host tree branches in early July. Winter is spent in the egg stage. Larvae hatch in early spring when foliage opens. The larval stage is an “inchworm” or “looper”, approximately 1½ inches long when mature. Larval coloring varies from green or light brown to black, depending upon population density. The typical color of the larva in heavy populations is dark brown to black, with a dark-red head, legs, and anal shield. The larvae feed for about 1½ months, and then pupate in a loose cocoon for six to ten days. The adult, a snow-white moth, emerges in late June or early July. There is one generation per year.
Natural enemies help keep populations of the elm spanworm in check. One of the most important is Telenomus alsophilae, a tiny wasp which parasitizes eggs. Persistent outbreaks on high-value stands may require treatment with chemicals.
Elm span worms feeding on oak.
FALL CANKERWORM, Alsophila pometaria (Harris)
The fall cankerworm is widespread in the northern part of the United States, ranging south through the Appalachian Mountains to North Carolina. Larvae defoliate many species of hardwoods, but in the South seem to prefer oaks, hickories, and ash.
