elm spanworm moth

not listed

NNR - Unranked

SNR - Unranked

not listed

Elm spanworm moth is a common, medium-sized, typical geometer moth. It occurs in the United States and southern Canada east of the Great Plains. It was accidentally introduced into Europe in shipments of asparagus. It is common in Minnesota.

Adults are found in July and August in deciduous forests and woodlands. Larvae are found from late May to early July. They feed on the leaves of a wide variety of deciduous trees and shrubs, including American hophornbeam, apple, ash, basswood, beech, birch, cottonwood, elm, hickory, maple, oak, and walnut.

Occasionally a population will experience a sudden, massive increase (eruption). When this happens, large areas of a forest may be defoliated. This is rarely a problem in parks or in yards.

Adults have a wingspan of 1⅜″ to 19⁄16″ (35 to 40 mm).

The antennae on the male are feather-like, with branches on both sides (bipectinate) from the base to the tip.

The wings are usually pure white, sometimes tannish white, and are unmarked except for a small black discal spot on the underside. The forewings are broad and have an angled rear (outer) margin. The hindwings have pointed projections along the outer margin.

Most adults are entirely white. Some individuals have varying amounts of lime green on the antennae, the abdomen, the legs, and the leading edge (costal margin) of the forewings.

The caterpillars are slender and long, up to 19⁄16″ (4 cm) in length. The color is variable. Most are green, but the color can range from yellowish green to brown or almost black. Darker colors are more common during outbreaks when population density is high. The upper side of the second, fifth, and eighth abdominal segments have a transverse ridge with a single hair (seta) at each end.

Wingspan: 1⅜″ to 19⁄16″ (35 to 40 mm)

Deciduous forests and woodlands

One generation per year: July to August

Adults rest with their wings held flat and spread out, or sometimes with their wings held vertically and tightly compressed above the body. They are active at night and will come to light, often in large numbers.

The female lays eggs on the underside of twigs. The eggs overwinter. Unlike other loopers, the caterpillars pupate on the leaves of the host, not in leaf litter on the ground or underground.

Leaves of deciduous trees and shrubs, including American hophornbeam, apple, ash, basswood, beech, birch, cottonwood, elm. hickory, maple, oak, and walnut.

Flower nectar

Sources

4, 21, 27, 29, 30, 71, 75, 82, 83.

Common

The genus Ennomos was formerly placed in the tribe Ourapterygini. An analysis of the the subfamily Ennominae (Beljaev, 2008) proposed a new generic composition of the tribe Ennomini based on unique characteristics of the male genitalia and on general morphology. Beljaev proposed the synonymization of the tribes Ennomini and Ourapterygini. A later molecular sampling of the family Geometridae (Sihvonenet al., 2011) suggested that the Ennomini, Ourapterygini, Nephodiini, and other taxa “constitute a well-supported clade.” This was supported by a more recent molecular analysis of New World Geometridae (Brehm et al., 2019). Brehm agreed with the synonymization of Ennomini and Ourapterygini.

Genera formerly in the tribe Ourapterygini are thus transferred to the tribe Ennomini. Ennomini now comprises the highest number of Neotropical genera (more than 100, including undescribed taxa) in a single tribe. The transfer has not been universally accepted.

Ennomos subsignaria elm spanworm moth

Ennomos subsignaria, elm spanworm moth, on siding of house, Milwaukee, WI, July 13, 2022. These moths are attracted to light.

Location: Milwaukee, WI

Ennomos subsignaria, elm spanworm moth, on siding of house, Milwaukee, WI, July 13, 2022. These moths are attracted to light.