What to Look For
The gypsy moth passes through four stages: egg, caterpillar, pupa, and adult moth. Only the caterpillars damage trees and shrubs in the spring of the year from May to early June. The caterpillars are voracious feeders, and have a large menu that includes several hundred host trees and understory plants.
Damage from feeding caterpillars can be severe. They may completely defoliate large areas of urban and woodland trees. Nearly every tree and shrub, that is commonly planted in the landscape, is a host for gypsy moth. The following information will help you identify the gypsy moth life stages, and hopefully some of the more common caterpillars that are often mistaken for gypsy moth.
If you reside in Iowa and you suspect gypsy moth as a new introduction to your area, please let us know by going to our Contact us page. We would be interested in taking a closer look.
Egg masses are tan colored when they are first deposited, and have a fine felt-like appearance. The female moth can find secluded locations for the egg mass, such as under the bark scales of a tree, but any surface has potential including tree branches several feet overhead. The color of the egg mass may bleach-out over the winter months, especially when exposed to direct sunlight and weathering.
Egg masses vary in size and shape, but generally range about the size of a quarter to a fifty cent piece. They may contain anywhere from 30 to several hundred eggs depending on the nutritional diet of the female caterpillar during her development. Caterpillars that develop on preferred hosts tend to emerge as adult moths with more potential reproductive capability.
The hatching of gypsy moth eggs coincide with the budding of most hardwood trees. Caterpillars emerge from the egg masses in early spring, or about the same time oak leaves are 1/3 expanded. This is usually in the month of May for Iowa depending on how warm the spring weather has been.
Caterpillars or larvae develop by going through a series of progressive molts by which they increase in size. The first caterpillar stage is small enough where strands of silk may be caught by the wind; thereby transporting larvae to new areas on air currents.
Older larvae have five pairs of raised blue spots behind their head, and six pairs of raised brick-red spots along their back. These spots indicate the gypsy moth caterpillar and are unique to the species.
Gypsy moth caterpillars also have large eyespots, or darkened areas on the front of their heads. Although not technically eyes that are used for sight, these eyespots are thought to help ward off predators. The eyespots of gypsy moth caterpillars are a unique trait of the species.
These characteristics are indicative. If you happen to be looking at a hairy caterpillar with raised blue and red dots along its back, and it has large eyespots, then it most certainly is a gypsy moth caterpillar.
Eastern tent caterpillar is most likely to be confused for gypsy moth since it appears about the same time in the year. To see common caterpillar look alikes that are often confused for gypsy moth, please visit our Gypsy Moth Look Alike page.
Caterpillars pupate into the adult moth during mid-summer. Typically this is in late June and early July in Iowa. Pupation may last from 7 to 14 days. Pupa are dark brown with only a few orange-yellow hairs, and may be found in any sheltered area where the caterpillars have rested.
Pupae may be found exposed on trees, the sides of buildings, and also in hard to find places. Pupae can be moved easily by unsuspecting people on any outdoor article, or motor vehicle including campers and trailers, and are some other ways this pest is transported long distances.
Female moths are white with brown markings. They are about 3 times larger than the male. Males are dull grayish-brown with brown markings. The most easily recognized feature for the male is the feather-like antennae.
When heavy egg-laden female moths emerge from the pupa, they emit a chemical 'pheromone' to attract the male moth. Since the female moths are so much larger than the male, they are not capable of flight. Male moths on the other hand are very capable of flight. They follow the pheromone plume emitted by the female moth by using their feather-like antennae to pick up the chemical signal.
Female moths will often lay egg masses in locations most convenient to them, which may include being deposited on any outdoor article or surface. Egg masses are often found hidden underneath bark scales on trees making them very difficult to find, on branches overhead, or they may be completely exposed and in the open.
The egg mass will remain dormant through the fall and winter. The next generation of gypsy moth caterpillars will hatch the following spring. This is usually in early May for Iowa depending on how warm spring temperatures have been.