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Fall Web Worm

Fall web worm nest
Fall web worm dark phase

About Fall Web Worm

Can live on elm, plum, chokecherry, poplar, willow, and other hardwoods.

Larvae are about 25 mm long, and are either pale yellow with red heads and reddish-brown spots or yellow-green with black heads, a broad dark dorsal stripe and black spots.  Moths are white, with reddish-orange front legs and a wingspan of 30 to 42 mm.

Pupae overwinter in cocoons in soil or duff.  Moths emerge in late spring or early summer and lay eggs in hair-covered masses on the undersides of leaves.  Larvae emerge about 10 to 14 days later and feed in groups of webbed nests constructed around leaves at branch ends.  By late summer the unsightly nests may be 1 m across and contain excrement, dried leaf fragments, and cast skins of larvae.  There are one to two generations per year.

Ornamental trees may become severely defoliated and unsightly.

To Control

When webs first appear, spray foliage with Bacillus thuringiensis (B.t.), carbaryl, acephate, chlorpyrifos, methoxychlor, or diazinon.  Except for B.t., these insecticides also will kill beneficial natural enemies of fall web worms.  Remove and burn branches with webs.