Horned spanworm moth

Hodges #

7010

Conservation Status

IUCN Red List

not listed

NatureServe

NNR - Unranked
SNR - Unranked

Minnesota

not listed

Description

Horned spanworm moth is a small geometer moth. It occurs across the United States and southern Canada. In the U.S. it is common east of the Great Plains and in the northwest but is rare or absent elsewhere. Adults are found from early June to late September in deciduous and mixed forests and woodlands, in meadows, and in parks. Mature caterpillars are found in late spring. They feed on more than 60 species of plants from at least 20 families, including deciduous and coniferous trees, shrubs, and herbaceous plants.

Adults have a ¾″ to 1″ (19 to 25 mm) wingspan. Females are larger than males.

The female has a ½″ to 9⁄16″ (12 to 14 mm) forewing length. The outer margin of both wings is always angled, the forewing especially so. The ground color is almost always whitish or cream-colored, rarely yellowish, and the markings are reddish-brown. The antemedial (AM) line is a single line that is mostly straight but curved sharply forward approaching the leading edge (costal margin). The postmedial (PM) line is represented by two lines (doubled). The inner line is slightly wavy and sharply bent forward approaching the costal margin. The outer line is bolder, wavier, and straight to the costal margin. The two lines converge twice, almost touching, before spreading far apart at the costal margin. The subterminal (ST) area, beyond the PM line, is darker purplish-brown on the inner half, pale on the outer half. All of the pale areas on the forewing are lightly shaded with numerous short, fine, horizontal lines. The veins are also dark. The hindwing is similar, but the entire ST area is dark.

The male has a ⅜″ to 9⁄16″ (10 to 14 mm) forewing length. The wing shape, ground color, and markings are all variable. The forewing is usually rounded, sometimes angled. The ground color is usually yellowish, sometimes whitish. There is often a dark blotch in the ST area covering part of the darkened inner half and extending into the outer pale half.

The caterpillar is up to ¾″ (2 cm) long and is instantly recognizable. The ground color varies from yellow to brown and is overlain by dark, medium, and light brown mottling. On each of the first and second abdominal segments there is a pair of curled, extendable, white-tipped tentacles (filaments).

Size

Wingspan: ¾″ to 1″ (19 to 25 mm)

Similar Species

Habitat

Deciduous and mixed forests and woodlands, meadows, and parks.

Ecology

Season

One generation per year: early June to late September

Behavior

The caterpillar often rests on an upper leaf surface with the body looped. It has been suggested that this mimics a fallen flower and its stamens. When alarmed, it inflates the filaments to twice their length.

The adult sometimes rests on the upper side of a leaf, where it resembles a dead leaf; on the underside of a leaf, where it resembles a dead patch; or on leaf litter on the ground, where it blends in with the background.

Life Cycle

Larva Food/Hosts

Plants from at least 20 families, including deciduous and coniferous trees, shrubs, and herbaceous plants.

Adult Food

Distribution

Sources

6, 7, 21, 22, 24, 27, 30, 75, 82, 83.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu. Accessed 6/5/2026).

Nematocampa resistaria (Herrich-Schäffer) in GBIF Secretariat (2023). GBIF Backbone Taxonomy. Checklist dataset https://doi.org/10.15468/39omei accessed via GBIF.org. Accessed 6/5/2026.

Quinn, Edward. M., and Ron Danielson. April 27, 2009. A Survey of Lepidoptera in Three Priority Areas of the Minnesota State Parks System. https://files.dnr.state.mn.us/eco/nongame/projects/consgrant_reports/2009
/2009_quinn_danielson.pdf.