How to identify a forest tent caterpillar moth
The adult is an unassuming moth, buff to tan or light brown, with a heavy furry body and a wingspan around 1 to 1.5 inches. Each forewing carries two roughly parallel dark oblique lines, and the area between them is often a slightly darker shade. Males have feathery antennae. This is not a showy moth, so the easiest way to know the species is often by its distinctive caterpillars and by mass emergences in outbreak years.
Where it lives
The forest tent caterpillar moth is native and broadly distributed across forested North America. Open occurrence records are highest in New York, Texas, Vermont, New Hampshire, and Minnesota, spanning northern hardwood forests as well as the southern parts of its range. It is tied to deciduous woodland and shade trees, and populations can swing from scarce to enormous over a span of a few years.
When it flies
Adults are on the wing from April through July depending on latitude, with southern populations emerging earlier and northern ones later. The flight period is fairly short for each location, following the spring-to-early-summer feeding of the caterpillars.
Caterpillar, host plants, and life cycle
The caterpillar is striking: dark with a row of keyhole or footprint-shaped white-blue markings down the back, edged with orange and pale blue lines along the sides. These larvae feed gregariously on aspen, oak, sweetgum, sugar maple, and other hardwoods, and large outbreaks can strip the canopy across whole woodlots. Despite the name, they do not spin a real tent like the eastern tent caterpillar; instead they lay down silk mats on trunks and branches where they cluster. After feeding, they spin yellowish cocoons, and the adults emerge to mate and lay band-like egg masses around twigs that overwinter.
How to see one at night
Adults come to lights during their late-spring and early-summer flight, so a UV or mercury-vapor light against a white sheet is the most reliable way to find one. UV beats a plain white LED for this and most other moths. As with all moths, the light works by disrupting their flight orientation rather than drawing them to a goal, so a warm, calm, dark night yields the most visitors. New to night lighting? See our mothing for beginners guide, compare it with the invasive spongy moth, or find out what's flying tonight where you live.