This spring we’ve had reports that populations of the native forest tent caterpillar (FTC)

are building in Windham, Windsor, Franklin, Lamoille, Orleans, and Rutland Counties. The

window of concern is May and June when the FTC larvae are actively feeding. Although caterpillar

development seems ahead of normal this year, there should be several more weeks

before they pupate, and defoliation will become more noticeable.

Trees that are particularly favored include sugar maple, ash and oak, but FTC feeds on

most deciduous species. Check your trees in late June. If defoliated, they should refoliate

within several weeks. Most trees can survive several years of defoliation.

Overwintering egg mass surveys can predict FTC defoliation for the following year. We are

available to conduct these fall and winter surveys for sugarmakers and timberland owners.

Egg hatch generally occurs as sugar maples break bud, but is staggered over several weeks

so you may observe caterpillars of different sizes throughout the season. Half-grown larvae

are sometimes seen congregating on tree boles or on man-made structures around homes.

Once they reach about 2 ½ inches in length, they stop feeding, form a cocoon in leaves,

bark, or other dark structures, and pupate.

When tree foliage is depleted, larvae migrate to other vegetation and become a nuisance to

homeowners. Even vegetable gardens may be consumed by this native insect when populations

are high. Caterpillars sometimes succumb to a malady known as Melt, Wilt, or Black

Death. Caused by a nuclear polyhedrosis virus (NPV), this disease is common during outbreaks

when the insects are in close proximity to one another.

Similar defoliation caused by other insects may complicate diagnosis. This year we’ve seen

an increase in eastern tent caterpillar (ETC). This close relative of FTC feeds on cherry

and apple, hatches a bit earlier, and can be easily misidentified as FTC. If the caterpillar is

associated with a “tent” and has a solid white stripe down the back, it’s an ETC. FTC larvae

have white, keyhole markings down the back. Forest tent caterpillars do not make a tent!

Click here for more information.

 

Article credit: Vermont Department of Forests, Parks and Recreation, Forest Biology Laboratory

Photo credit: Elise Schadler, VT Urban and Community Forestry