Spongy Moth (formerly "Gypsy Moth")
Introduction
The spongy moth (formerly “gypsy moth”; Lymantria dispar dispar) is a nonnative moth that has defoliated over 95 million acres of hardwood forests throughout the northeastern United States over the course of the past century. It is native to Europe and northern Africa but was brought to Massachusetts in 1869. Since then, it has spread southward through the northeastern states into southwestern Virginia and a major front is approaching Tennessee at a rate of approximately four miles per year.
Note about the name change: In March of 2022, the officially recognized common name of Lymantria dispar dispar was changed from European gypsy moth, to spongy moth as a part of the Entomological Society of America’s Better Common Names Project. The “spongy” descriptor refers to the spongy-like appearance of the egg masses. This page has been edited to reflect the name change. For more information, please see the link in the Resources section below.
The caterpillar stage of the spongy moth is what causes the significant defoliation in hardwood forests. These caterpillars are 1/16th of an inch long and go through five to six growth stages before entering the pupal stage. The larvae increase in size through each growth stage and develop five pairs of raised blue dots followed by six pairs of raised red dots on its back. They are covered in dark bristly hairs and easy to spot. The caterpillars can feed on hundreds of different species of trees and shrubs, with a preference for oaks, and their voracious appetites can quickly defoliate entire forests during outbreaks. After pupating, adults emerge June through July, depending on temperature and elevation. The adults do not have mouth parts and only have around one week to mate before dying.
Egg masses are laid from mid-June to early July. These masses are oval shaped, about 1 inch long and are covered with fine tan colored hairs. The female moth usually lays her egg masses in bark crevices, on the underside of branches, or under decks, chairs, firewood, lawn furniture, or on vehicles. The eggs hatch the following year in early to middle April when the hardwood trees start producing leaves.
The spongy moth travels in three main ways: crawling, ballooning, and accidental human transport. Female moths cannot fly. When the female emerges from pupation, she crawls to a sheltered spot to mate and lay her egg masses on bark, branches, or other objects like outdoor furniture or vehicles. The accidental movement of these egg masses on vehicles or in firewood and other unprocessed wood can transport the spongy moth egg masses hundreds of miles away where they may hatch and cause new outbreaks. The spongy moth caterpillars themselves can move around by crawling or by producing a fine silk thread that catches the wind and takes them to other trees, a process called ballooning.
The range of spongy moth extends over 19 states and has caused significant defoliation in many of these areas. While small scale defoliation events rarely cause significant permanent damage to trees, outbreaks of spongy moth may cover thousands of acres and may recur for multiple years, weakening trees over consecutive seasons. These forests weakened by repeated defoliations are more susceptible to a wide variety of other pests and pathogens, as well as abiotic stressors, that may cause tree mortality. The damage caused by spongy moth has had significant economic impacts throughout the northeastern U.S.
To date, there are no established spongy moth populations in Tennessee. The presence of isolated spongy moths has been detected in Tennessee every year since the beginning of the statewide trapping program in the 1970’s, but no detections have developed into established populations. Annually, Tennessee places traps to assess spongy moth detections, and once a positive identification has been made, an extensive pattern of traps are installed around that location. These traps help the Tennessee Department of Agriculture understand the source, extent, and direction of a possible infestation. Often, infestations can be eradicated through extensive trapping, but sometimes spray operations are necessary. The lack of established populations in Tennessee has been due largely to the success of the extensive trapping and treatments that have been conducted over the past 50 years.
Annual Survey
The Department of Agriculture and various partners install between 6 to 10 thousand orange or green Delta traps statewide each year. These traps are placed in a grid-like pattern that covers rural and urban environments. The traps contain a lure that attracts male moths that are flying during the summer, and once in the trap, the moth is confined by a thick layer of glue. Personnel check the traps for any moth catches, and if a suspect moth is found in a trap, the trap is sent to the Forest Health Specialist or the State Entomologist for identification.
Because of the potential economic and ecological damage that this moth is capable of, national programs to manage and slow the spread of spongy moth have been implemented in many states. By proactively trapping this moth along the leading edge of its spread, these programs have had a lot of success at slowing the rate at which it is spreading into new areas of the U.S., including Tennessee.
Since spongy moth has not established in Tennessee, management for populations is not currently necessary. For areas of the United States that have active infestations, cultural practices such as fertilizing, watering, or pruning help to keep trees healthy and strong if defoliated. Planting tree species that the spongy moth does not like such as bald cypress, black locust, yellow poplar, sycamore, red cedar, or holly may help. Additionally, reducing the number of places where the female moths can hide egg masses by keeping outdoor articles and debris under cover or inside can reduce accidental spread from active infestations.
If a population is detected, it can be eradicated through intensive trapping, or aerial or ground application of either biological or chemical pesticides. Silvicultural treatments such as pre-salvage thinnings, sanitation thinnings or post-outbreak harvests are some options used in areas where the threat of a spongy moth outbreak is near or present in a forested environment.
What Can You Do?
Learn to recognize the egg masses, caterpillars, and adults. Thoroughly inspect your vehicle, camper, outdoor furniture, and firewood for egg masses if traveling from a known area of spongy moth population. If an egg mass, caterpillar, or adult is found, immediately contact your county agent, professional forester, or the Division of Forestry. Early detection is very important to preventing major infestations. Do not move firewood.
