Caterpillars have voracious appetites and none more than this hairy Gypsy moth variety shown in this undated file photo. Credit: Dean Fosdick / AP

MONTPELIER, Vt. — The state of Vermont is seeing a large infestation of gypsy moth caterpillars this year that are defoliating many of the state’s trees, the Agency of Agriculture said.

The state has not seen a large outbreak since 1991, but the insects have been here in smaller numbers.

Gypsy moths are an invasive insect that first arrived in the United States more than 100 years ago and they have been expanding their range ever since.

Gypsy moths prefer oak trees, but when populations are high they will eat many types of leaves, including maple and pine.

Although gypsy moth caterpillars are damaging, otherwise healthy trees can often survive a few years of successive defoliation.

At the time of the last major outbreak, a fungus significantly decreased the gypsy moth population. The fungus is most abundant after periods of wet weather, but due to the droughts and dry weather the state has experienced over the last few years, the fungus has been limited.

Due to this combination of drought and defoliation, Vermont may see another year or two of high levels of gypsy moth activity unless the state sees some rainy seasons to increase the population of the gypsy moth-killing fungus.