During the highest outbreak years of the gypsy moth (Lymantria dispar) in Virginia populations were so high that the sound of the caterpillar's frass dropping from the tree canopy sounded like soft rain falling through the forest. For those whose homes were surrounded by highly infested trees, uncovered coffee cups were bound to receive extra flavoring; enjoying a meal on the porch was out of the question unless a large umbrella covered the table to deflect the small dark green balls of digested foliage continually falling from above.
Above: The wings of the gypsy moth are furled and crimped immediately following emergence from the pupa case. Within an hour, the wings gradually grow larger and lie flat along the body of the moth.
Since their accidental escape from the breeding location into the wild they have done millions of dollars in damage to eastern forests.
Fortunately, nature is now helping with their control: A natural fungus and a virus have kept their numbers in check for the last 10 years or so and aerial spray is not needed in as many areas in Virginia as during the highest outbreak years.
The baby caterpillars emerge from their egg masses usually at the end of April to early May in the Shenandoah Valley and Piedmont. They go through five instars, eating more vegetation as they get larger and become adults. The caterpillars are unmistakable with two rows of red and blue dots and long dark hairs. Pupation occurs in June or July, depending on elevation, and by then, the damage to trees and shrubs can be significant if populations are high. The adults moths breed - the female moth is quite large, averaging about one and a half in length - and lays her signature tan egg mass on tree trunks, the underside of limbs or the sides of structures. The larvae overwinter, emerging again the following spring.
It is believed that a new outbreak occurred in Oregon when an automobile part was sold on Ebay: the vehicle from which the part was taken was parked under a tree in the East and an gypsy moth had laid an egg mass on the part. It was installed on a vehicle in Oregon, the caterpillars hatched and a new infestation occurred. Each egg mass can contain up to 500 larvae.
It is difficult to predict when gypsy moth populations will once again increase in Virginia but hopefully we will not experience the substantial tree mortality that previous outbreaks have caused.
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