Fall Webworm (Hyphantria cunea)
Detailing the identifying qualities of the Fall Webworm, including physical features and territorial reach.
Updated: 8/28/2017; Authored By Staff Writer; Content ©www.InsectIdentification.org
The native Fall Webworm produces an active caterpillar that has expanded its geographical range across both oceans into two continents.
The Fall Webworm is a moth that comes in two colors: all white in the north, or white with brown patches (almost like a giraffe) in the south. The pronotum is hairy. Legs are white, or orange with brown on them. The name stems from its larval form, a caterpillar that spins a silky web with its newly hatched siblings. These webs can cover twigs, branches or even entire trees. It acts as a barrier, allowing the caterpillars to feed on the leaves of the host plant with a good degree of protection from predators. Both versions are now present in Europe and Asia. First sightings of them out of their native range began in the 1940's.
Females lay a carpet of light-green, spherical eggs on the bottoms of leaves. Caterpillars hatch and immediately begin eating and building a tent web to cover themselves. The caterpillars, like adults, come in two color forms. In its northern range, it has a black head and hairy yellow body with black dots along the dorsal (back) side. in the southern range, the head is orange. One to four generations each year can be produced depending on the climate. (Warmer climates breed more generations.) They feed on a large variety of tree leaves. Hickory, alder, elm, willow, mulberry, oak, poplar, sweetgum, birch, cherry, apple, and pecan trees are all hosts for Fall Webworms. They do not attack fruit and, though the webs are unsightly, they usually do not permanently damage a tree. They are active in the autumn and consume leaves right before the foliage dries up and falls off anyway. They are considered a pest to ornamental trees though because the purpose of an ornamental is to look attractive in the garden or park and large silk webs deter from those aesthetics.
Managment of Fall Webworms is not considered necessary. Certain species of wasps and flies are predators of this caterpillar, so a biological control exists.