The fingered dagger moth, also commonly called an alder dagger, was formerly classified as a separate species, Acronicta hesperida. This “western form” is now included in Acronicta dactylina and is no longer a separate species.
Fingered dagger moth caterpillars are covered on the dorsal side with dense orange hairs and white hairs laterally. A few longer white or black hairs stick out beyond the shorter hairs at the anterior and posterior ends of the caterpillar. There may be three dense dorsal tufts of black hairs on abdominal segments 1, 3 and 8. The face is black.
Widely distributed throughout North America, fingered dagger moths are found in moist forests. The caterpillars (or larvae) feed in late summer and early fall on deciduous trees and shrubs including birch, alders, willows, poplars, hawthorn and cottonwoods. Fingered dagger moths overwinter as pupae.
“Fuzzy” dagger moth caterpillars are urticaceous, that is, they cause a reaction similar to stinging nettle when touched. Fingered dagger moth caterpillars do not sting like wasps or bees. Instead, when their hollow hairs are touched, the hairs break and release a toxin from the poison glands to which the hairs are attached. These toxins protect the caterpillar from predators. In humans the toxin causes stinging, itching, a burning sensation and dermatitis.
This fingered dagger moth caterpillar was photographed on the Steep Canyon Trail at Silver Falls State Park in Marion County Oregon.