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Accidentally introduced to North America in the 1860’s the Gypsy Moth has become a major devastation among our forests.  They were a failed silkworm experiment that resulted in them spreading their range into the northeastern United States and southeastern Canada.  Their favorite trees are oaks and aspen but will eat the foliage of almost any tree even eating evergreen if it’s in need of food.  Since 1980 they Gypsy Moth has single handedly defoliated over a million acres of forest each year.

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Like most moths and butterflies the Gypsy moth goes through four stages: egg, larva, pupa and moth. Gypsy moths make their homes and lay eggs in tent shaped webs inside the tree branches or on tree trunks.  Egg masses are buff colored or may become a bleached white.  Only when it is in the caterpillar stage does it damage trees by eating the leaves, first by chewing small holes and then later by eating the entire leaf from the outside in.  The larvae increase in size by molting 5 or 6 times during their lifespan before they become an adult moth.  This happens in mid-June or July where they then go on to the pupal stage.  This stage takes anywhere from 7-14 days.  The male moth searches for the female and the female then lays her eggs.  At this time both moths die.  The larvae from the eggs develop after 6-8 weeks but remain inside their embryo to hatch next spring.

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During defoliation if more than 50% of the tree is eaten it will partially regrow its leaves by midsummer.  If the tree has been weakend by previous stresses such as drought they can be killed with one defoliation.

(dead trees in central Wisconsin due to infestation of the Gypsy Moth caterpillar)

The Gypsy moth does have a number of natural enemies including wasps, flies, beetles, ants, many birds, mice, shrews, chipmunks and squirrels. These animals somtimes flock where there are heavy infestations. In 1906 a large, green metallic ground beetle (Calosoma sycophanta) was introduced to try and reduce the population of Gypsy moths.  Disease may also be caused by bacteria, fungi or virus.  Weather can also play a role in whether or not the eggs will survive.  Periods of freezing and thawing in early spring will prevent the eggs from hatching.

Image via Wikipedia natural enemy of the Gypsy Moth

On a personal note I have seen many of these caterpillars and the damage they have done to the trees in central Wisconsin.  My parents live in the country and just sitting under a maple tree will have you covered in them as they fall off the trees.  Any time we find a nest in the trees we immediately remove and burn them.  My son has cut just one of the nests open and literally hundreds of them will fall out.  Getting rid of them anytime you see one is the best way to try and manage them without using pesticides.  Placing a small piece of plastic like a section of tarp around the trunk of the tree with double sided tape, grease or petroleum jelly on it will stop them from reaching the foliage.  If you have a favorite tree I highly suggest this if you have seen many of the caterpillars hanging around.  Ridding your yard of brush, sticks and old tires can also help with the population as it gets rid of the places that they go to hide.

(closeup of a caterpillar nest in central Wisconsin.  The dark portion is filled with hundreds of Gypsy Moth caterpillars.  In some places the infestation is so bad that a walk from the car to the tree will have you stepping on them the whole way, ick!)