Farmers, gardeners, and homeowners often bring little critters into the office for identification and management recommendations. Recently, a Steele county resident brought in a whitemarked tussock moth (Orgyia leucostigma) caterpillar. These are kooky-looking critters and therefore they attract our attention. They are distinct looking, will feed on several hardwood plants, and can cause skin irritation when handled.
The whitemarked tussock moth caterpillar has a hairy yellowish body with a bright red head.
They eventually grow 1 to 1½ inches long. A main distinguishing feature is the presence of four cream-colored square-ish tufts on top of their bodies. They also have two spikes of black setae (hair-like bristles) that extend forward beyond the head and a rear tuft of black setae at the back.
These caterpillars will feed on many hardwood trees and shrubs in Minnesota including apple, birch, dogwood, elm, linden/basswood and poplar. They will also feed on evergreens, including spruce, fir, hemlock, and larch. As for damage, young caterpillars cause windowpane damage, meaning that they feed on one layer of leaf tissue between veins, giving them a lacelike appearance. Older caterpillars will consume entire leaves except the midrib and large veins, and can cause significant defoliation. On evergreens, they feed on the needles.
This insect overwinters as eggs. Caterpillars hatch in the spring between mid to late May and the tiny, hairy caterpillars begin to feed and grow. Some drop from trees suspended by a silk strand.
These may balloon for a considerable distance to invade new landscapes. They will feed for about five to six weeks. In Minnesota, a second generation is produced with caterpillars hatching in August and feeding into September.
Whitemarked tussock moth caterpillars are susceptible to multiple diseases, parasites, and predators, which may help keep them under control and explain why they are an infrequent pest issue. By the time the caterpillars are large enough or have done enough damage to be noticed, they have probably finished feeding. Though they may still be eating for a while, they will soon be searching for a site to make their cocoons.
Applying an insecticide to control mature caterpillars is not effective. The best time to spray is when the caterpillars are young and actively feeding. It can be challenging to safely get an insecticide up into the canopy of tall trees; you will want to consider using a professional if you’re attempting to treat large trees.
While whitemarked tussock moth caterpillars are not a frequent or typically severe pest, you should proceed with caution if you’re tempted to handle them. Their unique, prominent bristles can be irritating to our skin, especially for people with sensitive skin.