Gypsy Moth Biology

The different stages of the gypsy moth life cycle are managed in different ways. You may see any one of these life stages, and want to identify whether they are gypsy moths.

Gypsy Moth Life Cycle

Eggs

The adult female gypsy moth lays eggs in masses in August and September. She covers the eggs with buff-coloured hairs, making the egg masses look like small pieces of cloth. The eggs hatch in the spring.

Look for the buff-coloured, spongy egg masses on the sheltered portions and crevices of items that are under or near trees. This includes all:

  • Outdoor equipment
  • Outdoor furniture
  • Outdoor toys and playground equipment
  • Fences
  • Tree trunks
  • Wood and lumber piles
  • Garden sheds and other gardening equipment
  • Recreational vehicles (RVs, boats, trailers)
  • Any other object that was stationary in the area during the months of July through August when the adults are reproducing

Eggs can easily be moved from one place to another. Look carefully at your belongings before you move them, to make sure that there are no gypsy moth eggs.

  gypsy moth egg mass
The white, female gypsy moth laying eggs
on the bark of a hardwood tree.
  Egg Mass

Caterpillars (Larvae)

The tiny larvae, or caterpillars, hatch from the eggs between early and mid-April. The caterpillars are responsible for the damage to trees and plants that happens during a gypsy moth infestation.

There are over 300 known hosts of the North American strain of the European gypsy moth.

Most Common Gypsy Moth Host Trees

Native trees

 

Introduced trees

Alder
Birch
Cherry
Dogwood
Douglas-fir
Hazelnut
Hemlock
Juniper
Larch

Maple
Oak
Pine
Poplars
Some cedars
Some true firs
Trembling aspen
Willow

 

Apple
Apricot
Ash
Beech
Cherry
Chestnut
Elm
Hawthorn

Holly
Linden
Oak
Peach
Pear
Plum
Redwood
Walnut

The newly hatched, small and hairy caterpillars move up host plants to eat the newly emerged leaves. It is at this stage that some can be blown by the wind to new locations. Their light bodies can be carried over several kilometers when the wind picks up small threads of silk that they make using special glands in their heads. This spring "ballooning" is one of the most important ways that a gypsy moth infestation can spread to new areas.

Gypsy moth caterpillars grow and change over a couple of months. They shed their skin several times, revealing a new look each time. By early July, they are fully grown and ready to pupate (transform to an adult within a cocoon).

Younger larvae feed mostly at night. Older larva will feed day and night, consuming huge amounts of green leaves. A single caterpillar can eat up to 1,000 square centimetres of foliage in their lifetime, or the equivalent of about 15 oak leaves.

Mature caterpillars are about six to seven centimetres long, darkly coloured, and quite hairy. Each has a double row of tubercles (bumps) along its back. They usually have five pairs of blue and six pairs of red tubercles, but sometimes all tubercles are either black or blue.

Many people are allergic to the hairs on the gypsy moth caterpillar, and notice skin rash or symptoms of respiratory allergies if they are exposed to the caterpillars.

Newly hatched caterpillars. A younger caterpillar. Note the hairy body and the coloured spots on its back.
An older caterpillar. Note that the coloured spots on its back are more obvious. Also, note the distinctive markings on the head.

Cocoons & Pupae

Feeding is usually completed by late June or early July. Most larvae then move to protected locations, such as bark crevices, to transform into an adult moth within a cocoon—a process called pupating. Pupating takes about 10 days for females and 13 days for males. All caterpillars in a population will pupate over a period of about one month, usually during July.

The gypsy moth caterpillars find a sheltered location in which to pupate and are normally found next to or very near the egg masses.

The pupae are dark reddish-brown, usually with a few yellowish hairs. Female pupae are much larger than male

An empty cocoon. Note cast-off caterpillar skin to the right of the cocoon.

Adults

Moths—the adult stage in the gypsy moth life cycle—start emerging from their cocoons in early August. Most emerge around late July, but they can continue into late August in south-coastal B.C.

Adult gypsy moths do not eat. They only live about a week—long enough to mate, and for the females to lay their eggs.

Male gypsy moths are brown. They have a small body and are strong fliers.

Female gypsy moths are white with black markings on the wings. They are much larger than males, but they do not fly. They attract mates using chemicals called pheromones. After mating, the female lays her eggs before she dies. Her eggs will hatch the following spring. Egg-laying is usually all done by early September.

Adult male gypsy moth. Note the feathered antenna. Adult female gypsy moth.