Gypsy Moth Caterpillars

Gypsy Moth

A major pest of hardwood trees, gypsy moth control is often necessary to prevent damage in backyards and many urban areas.

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In the mid 1800s, gypsy moth larvae (Lymantria dispar) that were being evaluated for silk production were blown from a window sill in Medford, Massachusetts. The first outbreak of gypsy moth occurred in 1889. By 1987, the gypsy moth had established itself throughout the Northeast and is now found throughout much of the Eastern United States. It is one of the most damaging pests of hardwood forests and urban landscapes, defoliating a million or more forested acres annually. Gypsy moths are spread over large areas primarily by shipment of infested nursery stock or any object on which eggs may be deposited.

Only the caterpillar stage of the gypsy moth feeds. When fully grown, they will be approximately 2 inches long, very hairy and have five pairs of blue dots followed by six pairs of red dots along its back. Adults are gray (male) or white (female) colored hairy moths with a 1-1/2 – 2 inch wingspan. Although both sexes are winged, the female moth does not fly.

Life Cycle

The female gypsy moth lays an egg mass, covering it with body hairs to act as insulation and to help protect the eggs from predators. Shortly after the female gypsy moth lays the egg mass, she dies, and the eggs wait out the winter until temperatures rise in the spring and a hatch begins. Upon hatching, small black headed gypsy moth caterpillars, climb to the tops of the trees where they may begin to feed on foliage or they may dangle from silk strands and drift in the wind to colonize other trees. Gypsy moth caterpillars go through five or six instars and feed from late April to mid June. Most of the feeding occurs at night to protect caterpillars from extreme heat and predation by birds during the day. When fully mature, caterpillars stop feeding, and change into pupae. Adult moths emerge 7-10 days later. There is one generation per year.

Gypsy Moth Control

  • Keep your yard as clean as possible. Remove discarded items, dead branches, stumps, etc., where the adult female moth is likely to lay egg masses. Destroy any egg masses that are found.
  • The Gypsy Moth Trap is used to monitor the moth population and may also prevent male moths from homing in on females.
  • Tanglefoot Pest Barrier or Sticky Tree Bands can be placed around tree trunks to help curtail the caterpillars movement into and out of the tree canopy.
  • Apply Bacillus thuringiensis, var. kurstaki or Monterey Garden Insect Spray (Spinosad) to the leaves of trees to kill gypsy moth caterpillars. For best results, sprays must be applied when caterpillars are young, less than one inch long. In instances where populations are high, two (or more!) applications five days apart might be needed.
  • Azatrol EC contains azadirachtin, the key insecticidal ingredient found in neem oil. This concentrated spray disrupts growth and development of pest insects and has repellent and anti-feedant properties. Best of all, it’s non-toxic to honey bees and many other beneficial insects.
  • Least-toxic botanical insecticides should be used as a last resort. Derived from plants which have insecticidal properties, these natural pesticides have fewer harmful side effects than synthetic chemicals and break down more quickly in the environment.

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