Sigmoid prominent

Description

Sigmoid prominent is a medium-sized, heavy-bodied, nocturnal moth. It is the most common of the four Clostera species found in Minnesota. The species name albosigma means “white S” and refers to the prominent curved marking on the forewing. Spring individuals are darker with more highly contrasting markings. Summer individuals are paler and less conspicuously marked.

The top of the head, the collar, and the top of the thorax are dark brown. The rest of the body is lighter grayish-brown. The male has a dark brown tuft at the tip of the abdomen.

The forewing is grayish-brown. The forewing is slightly concave on the costal (leading) margin and is rounded at the tip. It is crossed by four pale lines, the basal, antemedial, median, and postmedial lines. The antemedial and median lines are parallel and nearly straight. The median line is broken and does not reach the costal margin. The postmedial line is angled backward, forming a “V” with the median line at the inner margin, and forming a prominent white “S”-shaped bar approaching the costal margin. The white bar sharply delineates a dark reddish-brown or chestnut brown area. The cubitus (Cu) vein appears 3-branched.

The hindwing is nearly evenly grayish-brown without contrasting markings. The subcostal (Sc) vein and the anterior branch of the radius (R1) are fused together. The Sc+R1 and radial sector (Rs) are close together and parallel to at least the basal half of the anterior side of the discal cell then diverge.

The male antennae are comb-like with teeth-like structures on both sides. The female antennae are thread-like.

The caterpillar is stout and up to 1 3 ⁄16″ long. It has a dark, proportionally large head, and there is usually a pale brown spot above the face (frons). The thorax and abdomen are yellowish-buff and covered with downy, pale hairs (seta). Between the first thoracic segment (T1) and the second abdominal segment (A2) there are four indistinct orange or yellow lines separated by even more indistinct charcoal lines. There is a black knob on A1 that is nearly twice as large as a similar knob on A8. There is a broad, dark gray subdorsal stripe and a broad orange spiracular stripe. Mature caterpillars are seen from May to November.

Size

Total length: ⅝″ to ¾″

Wingspan: 1⅛″ to 1½″

Similar Species

Habitat

Deciduous woodlands and forests, and shrubby wetlands and fields

Ecology

Season

Mid-May to mid-August. Probably two generations per year.

Behavior

Adults are active at night and will come to lights. They rest with the wings folded tightly around the abdomen, which is raised into the air.

The caterpillar is a solitary feeder. During the day it curls up a leaf of a host plant and sticks it together with silk webbing, make a shelter where it can feed in safety. At night, it feeds in the open. Unlike all other prominents (family Notodontidae), this species does not squirt acid as a defense.

Life Cycle

Given the long flying time for this species, there are probably two generations per year in Minnesota.

The pupa overwinters.

Larva Food/Hosts

Mostly quaking aspen, but also poplar and willow, and sometimes alder, birch, maple, and elm.

Adult Food

Adults do not feed.