half-wing

not listed

NNR - Unranked

SNR - Unranked

not listed

Half-wing is a medium-sized, early season, typical geometer moth. It occurs in the United States and southern Canada east of the Great Plains. Adults are are among the first moths to be seen flying in early spring. They are found from late March to late May in forests and woodlands. Larvae feed on young leaves of trees, including American basswood, American elm, apple, birch, hickory, maple, oak, and poplar; and on woody shrubs, including blueberry, cranberry, and ninebark. They can defoliate small areas of a forest, and are considered a pest. However, they do not occur in numbers large enough to do serious damage.

The antennae have 46 to 48 segments. On the male they are feather-like with two branches on each segment (bipectinate). On the female they are thread-like.

The abdomen is slender. The upper surface is covered with flattened, elongated, deeply forked, hair-like scales.

Adult males have large wings in comparison to their light-weight bodies. The forewing length is ⅝″ to ⅞″ (15 to 22 mm) and the wingspan is 13⁄16″ to 19⁄16″ (30 to 40 mm). Most males have pale gray forewings with heavy, gray, grayish-brown, or brownish-black (dark) lines and a variable peppering of dark scales. There is no discal spot. The antemedial (AM) line is wavy and is shadowed by a broad dark basal band. The median line is broad and straight. The postmedial (PM) line is wavy, slightly scalloped or toothed, and shadowed with a broad dark band in the subterminal area. The PM line has a deep bend that approaches but does not touch the median line. The subterminal (ST) line is represented by a broken band of dark shading. The terminal line is thin. The fringe is the same color as the wing. The hindwing is similar to the forewing but lacks the dark bands and the median line is incomplete. Females do not fly. They have all four wings but they are very small and non-functional. The forewing length is just ⅛″ (3 to 4 mm).

The legs are pale gray or grayish-brown and are covered with a variable amount of scattered dark scales. The fourth segment (tibia) of the front leg does not have a spine at the tip. On the hind leg there are two pairs of spurs on the tibia.

A dark (melanistic) form is not uncommon. On these moths the base color of the wings is dark brown to almost black and the lines and veins are black.

The caterpillar, called spiny looper, is light bluish-gray and up to 1⅜″ (3.5 cm) long. It has numerous black pinstripes running the length of the body. There is an orange stripe bordered with thin black lines on each side close to the middle (addorsal). There is also an orange patch on each side of every abdominal segment around the breathing pore (spiracle). On the second, third, and eighth abdominal segments there is a raised ward below and behind each spiracle. Stiff, bristle-like hairs (setae) on the upperside of each abdominal segment rise from black pimple-like bases. The head has many small, scattered, black spots.

Male forewing length: ⅝″ to ⅞″ (15 to 22 mm)

Female forewing length: ⅛″ (3 to 4 mm)

Male wingspan: 13⁄16″ to 19⁄16″ (30 to 40 mm)

Forests and woodlands

One generation per year: Late March to late May.

The female deposits eggs in crevices in bark. When the eggs hatch, the caterpillar crawls or floats about on a silk thread (balloons) to find suitable foliage. Caterpillars feed for about a month and a half, passing through five stages (instars). They overwinter in the soil as pupa. Adults emerge from late May to late April.

American basswood, American elm, apple, birch, hickory, maple, oak, poplar, blueberry, cranberry, and ninebark.

Sources

21, 24, 29, 30, 75.

Common

Phigalia titea half-wing moth

Phigalia titea, half-wing moth, male, photographed on the house adjacent to Barnes Prairie, Racine Co., WI, on April 14, 2022.

Location: Barnes Prairie, Racine Co., WI

Phigalia titea, half-wing moth, male, photographed on the house adjacent to Barnes Prairie, Racine Co., WI, on April 14, 2022.

Location: Woodbury, MN