University of Maryland Extension

Gypsy Moths - Trees

mature gypsy moth caterpillar
Mature gypsy moth caterpillar

 gypsy moth and egg mass
Gypsy moth and egg case

Gypsy moth is a serious pest of oak trees. Gypsy moth prefers oak but will also feed on sweet gum, linden, willow, birch, apple, alder, boxelder, hawthorn and blue spruce. Gypsy moths do not spin webs or make sacks in trees. Adult female moths are white with black spots and cannot fly. They lay felt-like tan egg masses on trees, rocks or wherever they can crawl to.  Eggs are laid in the early summer. There is one generation a year and winter is spent in the egg stage.
hatch begins in late April or early May depending on the temperature. Young caterpillars are black and chew small holes in the leaves. Feeding begins in early May, which is the best time to control the caterpillars. B.t. sprays are very effective on the small caterpillars. Large caterpillars (see above photo) may consume leaves to the midrib. Caterpillars grow up to 2 inches in length and have 5 pairs of blue dots and 6 pairs of red dots. They are more difficult to control than the young caterpillars.

gypsy moth defoliation
Gypsy moth damage

Management

  • Plant resistant trees such as red cedar, sycamore, red spruce, American holly, tulip poplar, and catalpa.
  • Destroy egg masses before April when egg hatching begins.
  • Use sticky barrier bands to trap young caterpillars before they enter treetops.
  • Use hiding bands to provide a refuge for migrating caterpillars that can then be removed and destroyed.

Use Bt (Bacillus thuringiensis) products to control young caterpillars.  If you are unable to spray your treetops, hire a professional arborist.

Additional Information

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