The yellownecked caterpillar (Photo 1) occurs throughout much of the United States, but is most common in the area east of the Rocky Mountains. It is reported to feed on foliage of a variety of trees including oak, maple, walnut, butternut, hickory, apple, honeylocust, basswood, birch, and elm. In Alabama, the caterpillar is most commonly found on oak.
The insect spends the winter and spring as a pupa (Photo 2) in the soil. Adults generally begin to emerge in July. The moth is similar to the walnut caterpillar moth. It is reddish brown with four narrow dark lines across each front wing; margins of wings are scalloped. Wingspan is 45-50 mm. Females lay eggs in clusters of 50-300 on the lower surface of leaves (Photo 3). Larvae usually begin to appear in late July or early August, usually about the last week of July or first week of August in the Auburn vicinity.
Newly hatched larvae (Photo 4) have black heads. Bodies are mostly red with patches of yellow on the back and alternating yellow and red lines along the sides. Early stage larvae feed in groups, often side by side, skeletonizing the lower surface of the leaf (Photo 4). Skeletonized leaves turn tan or brown; small clumps of these (Photo 5) are early evidence of caterpillar presence. Older larvae continue to feed in colonies but consume the whole leaf (Photo 6). As larvae develop, body color changes; mid-to-late-stage larvae (Photo 7) are red with conspicuous yellow to white longitudinal stripes, last-stage larvae (Photo 1) have black bodies, yellow or white stripes, and a conspicuous yellow collar, or "neck" behind the black head. The full-grown caterpillar is about 50 mm long, and sparsely clothed with white hairs.
Colonies of caterpillars of varying ages may be found through August and September into mid-October. During development, larvae leave the foliage periodically and congregate on branches to rest and molt (Photo 7). If disturbed, they assume a characteristic alarm position with head and rear end raised. When caterpillars are fully grown, they leave foliage, enter the soil, pupate, and remain as pupae in the soil through winter. There is one generation per year.
Typically, feeding colonies defoliate one branch then move to another. On large trees with ample foliage, only a few branches may be defoliated by the time larvae complete development. However, small trees with limited foliage can be completely stripped of leaves by a single colony. Healthy trees usually survive and recover; however, defoliation can cause dieback of branches and twigs, loss of growth, or even tree mortality, if defoliation continues through several consecutive years.
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All photos courtesy of Lacy L. Hyche