This graphic represents general ranges of gypsy moth life stage development for Minnesota. Cooler seasonal temperatures and/or more northerly latitudes can cause a clockwise shift of these ranges. For example, in northeast Minnesota, eggs may never reach 100% emergence and adults may appear into October.
Eggs are laid in a fuzzy, tan-colored mass. The egg mass contains 500-1,000 eggs and is about the size of a quarter. Eggs are laid during late summer and hatch the following spring when the weather is right. Egg masses can be found on living and/or inanimate objects, including nursery stock, logs, roof eaves, in wheel wells or outdoor household articles like firewood and lawn chairs.
The caterpillar hatches from the egg and grows to a length of 2½ inches as it matures. Its body is covered with hairs to protect it from predators including curious humans. Be careful - if you touch it your skin might get irritated! Along its back the caterpillar has five pairs of blue spots near the head, followed by six pairs of red spots. It actively feeds on plant foliage from late spring through mid-summer, when it develops into a pupa.
The pupa is an immobile stage of this insect's life. Though it appears inactive, it is very busy inside transforming from a caterpillar into an adult moth. Found mid-summer, it is dark reddish-brown, leathery in appearance, and often tethered to an object with silk strands. It can range in size from ¾ inch to 1½ inches long.
The adult female moth is white with brown jagged markings on her wings. Her wingspread ranges from 1 to 2 inches but she cannot fly because her body is so large and heavy with eggs. She releases a pungent sex attractant (pheromone) that only the male moths can smell so they can fly to her and mate. The female produces one egg mass and dies.
The adult male moth has feathery (plumed) antennae that are so sensitive they can "smell" a female a mile away. His body can be light beige to dark brown with black jagged bands on brown forewings. His wingspread ranges from only ¾ to 1½ inches yet he is a strong flyer and capable of mating with several females. Adult moths are typically active from late summer through early fall.
As animals and plants interact with each other over millennia, they develop mechanisms to increase their chances of survival. For example, the gypsy moth caterpillar is so hairy that birds and rodents think twice about eating it as they may end up with irritated skin around their eyes and mouths. Nevertheless, some predators will take that risk in order to have a bite to eat.
Another example is the behavior of the moth. The caterpillars are most active at night, dining on leaves by moonlight. They rest in a sheltered area during the day to avoid being attacked by birds.
Birds are just one problem though. The white-footed mouse is a rodent that eats gypsy moth caterpillars and pupae on and near the ground while they are resting. Mouse predation may be a very important factor in keeping small gypsy moth populations from getting bigger.
Smaller enemies include a number of tiny parasitic wasps and flies whose larvae feed on gypsy moth eggs or caterpillars. The adult female protects her eggs from predators by wrapping them in a mat of tiny hairs from her own body. Some of these small insects have been put into service by scientists trying to find a way to control large populations of gypsy moth.
On a microscopic level, a fungal pathogen called Entomophaga maimaiga has been studied and found to provide significant control of gypsy moth outbreaks. Wet conditions during springtime encourage the natural growth of the fungus. Spores from the fungus must be ingested by the caterpillar. Once inside, the spores start growing and eventually kill the caterpillar.
Gypsy moths are susceptible to a virus called NPV. When there are high numbers of caterpillars very close to each other, the virus is easily passed along. The caterpillars get sick and die very quickly, and some outbreaks have been virtually eliminated after NPV is introduced. NPV has been mass produced for control of gypsy moth and is sold under the brand name Gypcheck.
Arrest the Pest
Minnesota Department of Agriculture (MDA), 625 Robert Street N, St. Paul, MN 55155-2538, firstname.lastname@example.org