Gypsy moth life cycle infographic

Gypsy Moth life cycle infographic.

Updated: August 3, 2021
By Nancy Stewart

The European gypsy moth was brought to North America in 1869 by an entrepreneur who hoped to cross breed it with the silk worm, to create a hardy silk-producer that would be easy to raise and inexpensive to feed. He was unsuccessful, and unfortunately, several gypsy moths escaped and established a wild population. By 1890, they had begun defoliating trees in his Massachusetts neighborhood. More than a century later, the gypsy moth has expanded its range throughout Northeastern United States and Canada, west to Minnesota and south to North Carolina to be one of the most significant pest of shade trees and forests.  

There are many telltale signs that gypsy moths are invading your trees. The most obvious is gypsy moth egg masses, which are fuzzy, tan in color, and about the size of a nickel or quarter. The eggs masses are laid individually or in large clumps in protected places. Although there are a few native predators of the colorful caterpillars that hatch (including mice, shrews, and some birds), these insects can ravage a tree, feeding on unripe tissues of annual shoots, flowers and buds, and killing about 15% of the trees. In the long term, this mortality and defoliation can cause changes in tree species composition of the forest. Regenerating tree species may be less valuable to wildlife and less valuable as timber. This then causes a ripple effect throughout the ecosystem.

The Maryland Department of Agriculture has a Forest Pest Management Section (FPM) which manages this pest using an integrated management approach. The purpose of the integrated pest management approach is to have maximum impact on the pest species with minimum impact on non-target organisms, including humans. FPM monitors the presence and severity of gypsy moth infestations using surveys. Based upon surveys, integrated management is used to determine the best strategies to help minimize moth and caterpillar populations and damage. These strategies include biological, cultural, manual, and chemical controls.

What methods can be used to control gypsy moths? The key is understanding the life cycle. Several biological controls have been used, including the introduction of an egg parasitoid wasp, a ground beetle, and the use of biological pesticides. There are many chemical insecticides such as acephate, bifenthrin, and carbaryl that can be used to help minimize the gypsy moth devastation. However, some insecticides can harm non-target species in forests and streams. If not used properly, they can also harm humans. Be sure to read product labels carefully and follow the recommended guidelines.

FPM may recommend spraying with aerial treatments in areas threatened with defoliation. This method of control is particularly useful for large forested areas. Bacillus thuringiensis (Bt), a bacteria, or the insecticide Dimilin are used in Maryland depending upon such factors as the level of infestation, location, logistics, and public concern. In May 2021, Maryland’s gypsy moth suppression program focused on spraying sections of the lower Eastern Shore (Wicomico and Worcester counties). The rest of the state did not require treatment. For more information go to the Gypsy Moth Cooperative Suppression Program.

In addition to chemical and biological treatments, there are manual and cultural ways to defend against the gypsy moth. These include a band of either burlap or other cloth or sticky tape wrapped around the tree trunk; pheromone traps; soapy water; and good old squishing.

Landowners can also use the life cycle to combat gypsy moths. From May to July, hand pick caterpillars by gently shaking the tree so the caterpillars fall from the leaves. Place the fallen caterpillars  in soapy water to be destroyed. From June – August, the larger caterpillar will be trapped in burlap banding. The burlap wrapping will also be helpful in July and August, by trapping the female moths before they crawl up the tree and lay eggs (fun fact, female gypsy moths are flightless). During these months, pheromone traps can be hung in trees to attract male moths. Once trapped, they can also be place in soapy water.

November to late April is a great time to destroy egg masses. Survey your property for egg masses and scrape them from surfaces into soapy water to destroy them. In the spring and fall, plant flowers, herbs or shrubs beneficial to wildlife to attract birds and other critters likely to consume the gypsy moths.

Keep your trees healthy to better ward off attacks by watering trees in time of drought as well as fertilizing and pruning them. A healthy tree can sustain a heavy defoliation and suffer minimal damage. But several consecutive years of defoliation can kill even the healthiest tree. Drought can further stress a tree, making it more susceptible to gypsy moth damage.

The history of the gypsy moth in the U.S. is a stark example of the devastating impact an introduced species can have on an ecosystem.  The gypsy moth is here to stay. As stewards of the land, it’s up to us to keep the gypsy moth in check by walking our woods often, keeping an eye open for their presence, and taking the steps necessary to minimize their impact. Be sure to contact your local forester if you have questions or concerns about gypsy moths in your woodlot.