American Dagger Moth Caterpillar

The American dagger moth caterpillar is the larval stage of Acronicta americana, a night-flying moth in the family Noctuidae found throughout much of the eastern and central United States and southeastern Canada. Its thick coat of yellow-white setae (hairs) gives it a soft, almost toy-like appearance, but the long black hair pencils projecting from the front and rear of the body set it apart from most other hairy caterpillars.

This species is most often noticed in late summer and early autumn, when full-grown larvae leave their host trees in search of a sheltered spot to spin a cocoon. Because they wander across sidewalks, patios, and tree trunks during this dispersal phase, they are one of the more commonly photographed caterpillars of the season.

Despite the conspicuous hair pencils, the caterpillar itself plays a modest ecological role as a folivore of deciduous trees, and its presence rarely causes lasting harm to a healthy, well-established tree.

• Body densely covered in soft, pale yellow to cream-white hairs (setae)
• Four to six long, black 'hair pencils' project forward and backward from the body, with two extra-long black tufts near the middle of the back
• Body length reaches about 5 cm (2 in) at maturity
• Head is small and dark, mostly hidden beneath the hair coat
• Lookalikes include other tussock and dagger moth caterpillars, but few combine yellow fuzz with black pencil tufts at both ends

Found across the eastern two-thirds of the United States and adjacent Canada, this caterpillar feeds on a wide range of deciduous hardwoods including maple, oak, elm, birch, willow, and ash. It occurs in forests, woodlots, parks, and shade trees in suburban yards, with larvae most visible from midsummer through fall as they finish feeding and begin to wander.

Caterpillars feed alone rather than in groups, chewing irregular holes in the leaves of their host tree. When fully grown they descend from the canopy and search out bark crevices, leaf litter, or other sheltered surfaces to spin a grayish silk cocoon incorporating their own body hairs. As a folivore, the species contributes to nutrient cycling in forest canopies and serves as a food source for birds and predatory insects able to handle its hairy defenses.

Adult moths lay eggs on host leaves in late spring or early summer. Larvae hatch and pass through several instars over the growing season, growing progressively hairier and developing their signature black pencils. In fall, mature larvae spin cocoons in bark crevices or leaf litter and overwinter as pupae, with a single generation completed per year across most of the range.