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Trees in the forest

ABOUT GYPSY MOTHS (Lymantria dispar) | Photos | Control Options | Links to More Info

The Gypsy Moth is an invasive insect introduced to the U.S. in 1869. It has been spreading ever since. It was first seen in CT in 1905. Major outbreaks occurred in CT in the early 1970s and late 1980s, and again in 2005-2006.. In 2016 and 2017, a serious Gypsy Moth (Lymantria dispar) outbreak caused extensive damage to trees and shrubs in northeastern CT. The 2016 infestation was severe. In 2017, it was less severe but more widespread. If we have another dry spring and summer, damage to our forests could be devastating.

Downloads from the CT Agricultural Experiment Station:

Gypsy moths will feed on over 500 species of trees and shrubs. (One caterpillar can consume 11 square feet of foliage.) They prefer oak, apple, birch, poplar and willow. During heavy infestations, they will eat almost any foliage. If Gypsy Moths completely defoliate a pine or hemlock in year, it will probably die. Deciduous trees (which drop their leaves in the fall) can die if they are defoliated 3 years in a row, especially if they are already under stress (old, crowded, drought conditions.) The caterpillar droppings also create a slippery mess.

Female gypsy moth Male gypsy moth Gypsy moth laying eggs Gypsy moth caterpillar Gypsy moth pupa

Female Moth: Cannot fly. Attracts male with pheromones. Does not feed, and only lives about 6-10 days.

Male Moth: Can fly, and travel long distances to find a female. Does not feed, and only lives 6-10 days.

Eggs: 100-1000 eggs laid on tree bark in mid-summer, overwinter, and then hatch in late April/early May of the following year.

Caterpillar (Larva): 4 to 5 instars (larval stages). Stages 1-3 stay in the tree tops. Stages 4-5 climb down to the ground, molt, and then climb up to the foliage again to eat more before turning into pupae. The wind spreads small caterpillars on their silken safety lines.

Pupa: Caterpillars pupate in june to early July in CT, turning into moths after about 10 - 14 days.


  • When the caterpillars are small, some birds, ground beetles, and small rodents (e.g., white-footed mice, shrews) will eat them.
  • Tiny parasitic black wasps (Ooencyrtus kuvanae) also lay their eggs in gypsy moth eggs. The wasps overwinter in leaf litter and come out in mid-April to attack egg masses. They can only parasitize 20-30% of eggs (because they can only reach the outermost eggs in a mass.)
  • There are some naturally occurring infections that can kill gypsy moths: (1) a fungus called Entomophaga maimaiga (originally released in 1910-1911) can kill caterpillars if May and early June are wet. Infected caterpillars hang head down or in a V shape on the tree trunk. (2) Another less common virus called NPV will kill the caterpillars. It is found in a commercial product called Gypchek. (3) Bacillus thuringiensis var. kurstaki (BTk) affects caterpillars of moths and butterflies. It has to be eaten to work (thus has no effect on pupa or moths). It can be applied by commercial applicators/homeowners, and works best on young caterpillars (late April to early May, in 2 applications 1 to 2 weeks apart.)
  • Completely soak egg masses with canola oil spray before hatching. Insecticidal soap, mineral oil, or soybean oil also work.
  • Scrape off egg masses and destroy by putting them into a container of soapy water and dispose in the trash. Eggs that fall to the ground/are stepped on will still hatch.
  • For individual trees, put up a barrier band made of overlapping bands of duct tape (sticky side out) and replace as necessary, to catch the later stage caterpillars that descend trees at night and go back up during the day to feed. (Some caterpillars will get underneath.) You will have to periodically replace the tape once the bodies create a bridge over the sticky stuff. (Do NOT apply petroleum products such as Tanglefoot directly to bark.)
  • Make a burlap barrier band trap and put it on the trunk of the tree. Wrap a piece of burlap around the tree trunk, and tie it in the middle iwth twine. Drop the top half of burlap over twine and over the bottom half of burlap to create a skirt. Collect caterpillars in late afternoon and sweep them into a bucket of soapy water. See more info and video.
  • A blowtorch will probably kill egg masses, but if used too long, can damage the cambium of the tree, affecting wood quality and health.
  • A licensed arborist can spray tall (over 15 feet) specimen trees with an insecticide like Gypchek, which uses the NPV virus. Ask what insecticide is being used, and request something that targets gypsy moths and does not decimate beneficial insect populations. Some pesticides are restricted use, and can only be purchased and applied by a licensed applicator.
  • Commercial traps that use pheromones to catch male moths do not work well, and are not worth the money.
  • Aerial spraying is no longer done, due to toxicity.
  • If valuable stands of wood are damage, harvest promptly before trees degrade due to weather/other insect infestations. Consult a licensed forester (not just a logger) to get the market price for your wood. A licensed forester can also help you regenerate your forest in a sustainable manner with non-invasive plants.
  • Movement of wood in gypsy moth ranges is quarantined by the USDA. CAES inspects certain plant shipments destined for gypsy moth-free areas.

More Information and References:

Conservation Commission
How beautiful the leaves grow old.  How full of light and color are their last days.

- John Burroughs