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Fall Webworm

Fall Webworms

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For several weeks white webs on the tips of branches have been apparent on many trees.  These silken tents are the work of the Fall Webworm (Hyphantria cunea), a moth most associated with its larval stage. Fall Webworm caterpillars construct a web over the end of a branch, enclosing leaves on which they feed.  As the hairy, white caterpillars grow, they enlarge the web to encompass more leaves, with tents sometimes extending two to three feet.

Often mistaken as the work of Eastern Tent Caterpillars, the tents of these two moths can be distinguished by the season they appear (ETC are active in the spring, Fall Webworms in the fall) as well as the location of the tents (ETC are usually in the crotches of trees, Fall Webworms at the tip of branches). As soon as the eggs hatch in early summer, the Fall Webworm larvae begin to spin small silk webs over the foliage of the deciduous trees on which they feed (over 90 species). By fall the tents are conspicuous. A look inside one  reveals caterpillars, dead partially-eaten leaves, and fecal droppings.

The larvae feed together inside the increasingly large web for roughly six weeks, at which point they often start feeding independently before pupating in the ground over the winter and emerging as adult white moths the following summer.

If your favorite tree has one or more Fall Webworm nests in it, there’s no cause for alarm. These caterpillars may defoliate a tree occasionally, but rarely kill it, and usually only build tents on a handful of branches, if that. The larvae have more than 50 natural predators and 36 parasites that help control them. Also bear in mind that Fall Webworms do not eat the buds of next year’s leaves and the leaves they are feeding on will soon to drop to the ground. Next year leaves will appear on the currently affected branches with no sign of last year’s damage.

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