Some Anoka County residents were startled from sleep Wednesday by the drone of airplane engines at 6 a.m. They can expect a similar wake-up call in a week to 10 days.

The Minnesota Department of Agriculture was using aerial spray to attack an infestation of gypsy moths in Oak Grove. The spraying covered 513 acres where an infestation was discovered in the fall. A second application will be needed to complete the treatment, department officials said.

Gypsy moths arrived in Minnesota in the 1970s. As a non-native species, they have no natural predators, and in their caterpillar stage, a population of gypsy moths can quickly strip the leaves from many acres of foliage. The critters aren't choosy about what they eat, feeding on more than 300 types of trees and shrubs — but oak, poplar, birch and willow are among their favorites.

The moths lay their eggs in the fall, in masses that look like fuzzy, brown spots. The egg masses can be found on trees, firewood, even outdoor furniture.

The weapon used against the moths is Bacillus thuringiensis var. kurstaki (Btk), a naturally occurring bacteria that's widely used in organic gardening. Agriculture Department spokesman Allen Sommerfeld said the bacteria poses no threat to humans or pets, although people may prefer to keep themselves and their pets inside while spraying is taking place. The spray works best if applied early in the morning, Sommerfeld said, apologizing for the inconvenience.

"But gypsy moths and what they can do to the trees if left unchecked is a bigger inconvenience," he said.