Biology & Life Cycle
Gypsy moth undergoes four developmental life stages; these are
the egg, larva (caterpillar), pupa, and adult. Gypsy moth females
lay between 500 to 1,000 eggs in sheltered areas such as underneath
the bark of trees. The eggs are covered with a dense mass of tan
or buff-colored hairs. The egg mass is approximately 1.5 inches
long and 0.75 inches wide. The eggs are the overwintering stage
of the insect. Eggs are attached to trees, houses, or any outdoor
objects. The eggs hatch in spring (April) into caterpillars.
Caterpillar (Larval Stage)
Gypsy moth caterpillars are easy to identify, because they possess
characteristics not found on other leaf-feeding caterpillars. They
have five pairs of blue dots followed by six pairs of red dots lining
the back. In addition, they are dark-colored and covered with hairs.
Young caterpillars primarily feed during the day whereas the older
caterpillars feed at night. When present in large numbers, the older
caterpillars feed day and night. Young caterpillars spread to new
locations by crawling to the tops of trees, where they spin a silken
thread and are caught on wind currents. Older caterpillars are approximately
1.5 to 2.0 inches long. Gypsy moth caterpillars do not produce a
web, which distinguishes it from web-making caterpillars such as
the Eastern tent caterpillar, Malacosoma americanum and the
fall webworm, Hyphantria cunea. The Gypsy moth larval stage
lasts approximately seven weeks.
In early summer (June to early July), Gypsy moth caterpillars enter
a pupal or transitional stage. The pupae are dark brown, shell-like
cases approximately two inches long and covered with hairs. They
are primarily located in sheltered areas such as tree bark crevices
or leaf litter. Adult Gypsy moths emerge from the pupae in 10 to
14 days. They are present from July into August. Females have white
to cream-colored wings, a tan body, and a two-inch wingspan. Female
Gypsy moths cannot fly. Males, which are smaller than females, with
a 1.5-inch wingspan, are dark-brown and have feathery antennae.
Both the adult female and male can be identified by the inverted
V-shape that points to a dot on the wings.
Gypsy moth has only one generation per year. Gypsy moth populations
will go through cycles in which the populations will increase for
several years then decline, and then increase again. Area-wide outbreaks
can occur for up to ten years, but generally population densities
in localized areas remain high for two to three years.
Adapted from Entomology Fact Sheet, NHE-153 written by Raymond
A. Cloyd and Philip L. Nixon, Department of Natural Resources and
Environmental Sciences, University of Illinois, Urbana, Illinois,
in cooperation with the Illinois Natural History Survey.