Taxonomy & Identification

Family: Erebidae (Tiger & Tussock moths; formerly Arctiidae).
Common name: Harris’s Tussock Moth.
Appearance (adult): A medium-sized, pale moth with light gray or tan wings, sometimes with faint darker spotting or banding. Forewings are generally unmarked compared to its close relatives (Halysidota tessellaris and Halysidota cinctipes).
Caterpillar: Covered in tufts (“tussocks”) of yellow, white, and black hairs. Caterpillars resemble those of other Halysidota species and can be difficult to distinguish without close inspection.

Distribution

Native to eastern North America. Range extends from the Great Lakes (including Illinois/Chicago area) through the Northeast and into parts of the Southeast.
Locally present but not nearly as abundant as the better-known White-marked Tussock Moth or other Halysidota species.

Eggs:
- Laid in clusters on the undersides of host plant leaves.
- Overwintering usually occurs in the egg stage.
Larvae (Caterpillars):
- Emerge in late spring or early summer.
- Feed gregariously at first, then disperse.
- Caterpillars are hairy, which deters predators and can cause mild skin irritation if handled.
Pupae:
- Formed in loose cocoons made of silk and caterpillar hairs, often in leaf litter or sheltered bark crevices.
Adults (Moths):
- Emerge in midsummer.
- Nocturnal, attracted to lights.
- Do not feed; their role is strictly reproduction.

Generations: Usually one generation per year in northern climates like Chicago.

Herbivory: Caterpillars feed on the leaves of various deciduous trees, contributing to natural pruning and nutrient cycling.
Food web contribution:
- Caterpillars serve as prey for birds (particularly cuckoos, which are adapted to eating hairy caterpillars), predatory wasps, and tachinid flies.
- Adults serve as prey for bats and night-flying insectivorous birds.
Hair defenses: Caterpillars’ hairs provide protection, but also serve as food sources for specialized predators and parasitoids.

Halysidota harrisii larvae feed on a variety of hardwoods. Documented host plants include:

These are all native to Illinois/Chicago region and excellent for supporting this moth.

Oaks (Quercus alba, Q. rubra, Q. macrocarpa): Keystone trees that support hundreds of Lepidoptera species, including this moth.
Hickories (Carya ovata – Shagbark Hickory): Very high-value host.
Black Walnut (Juglans nigra): Excellent host, though large and best suited for spacious yards or parks.
River Birch (Betula nigra): A smaller tree, good for urban/suburban planting.
Willows (Salix nigra, S. discolor): Shrubbier willows work well in wetter spots.
American Elm (Ulmus americana): Still valuable despite past Dutch Elm Disease losses; disease-resistant cultivars available.

Site: Choose sunny to part-shade spots depending on the species. Most thrive in well-drained soils; willows prefer moist sites.
Soil: Oaks, hickories, and walnuts prefer slightly acidic to neutral loam; birches like moist but well-drained soil.
Water: Provide supplemental watering the first 2–3 years until established.
Diversity: Planting multiple tree species increases resilience and supports a broader moth and insect community.

Avoid broad-spectrum pesticides, which can decimate caterpillar populations.
Leave leaf litter and fallen branches in at least part of your yard—important pupation habitat.
Consider “soft edges” (native shrubs and understory plants beneath trees) to provide microhabitats and shelter.