armyworm moth

10438

Common, sometimes abundant

Two or three generations per year: March to November

Fields, meadows, gardens, and agricultural crops

Armyworm moth, also called true armyworm and the white speck. is a migratory wainscot moth. It is medium-sized for a moth, large for a wainscot moth. It occurs in Europe, northern Africa, Iceland, North America, Central America, and northern South America. It is common throughout the United States and Canada, common and sometimes abundant in Minnesota. It does not survive cold winters. Adults migrate south in the fall and a later generation disperses north in the spring. Adults are found in Minnesota from March to November. Larvae (caterpillars) feed on leaves and sometimes seed heads of mostly grains and other grasses in the family Poaceae, but also many broadleaf plants close to their infestations. They are often a serious agricultural pest, especially on wheat and corn.

Adults are ¾″ to 1″ (20 to 25 mm) long and have a wingspan of 1⅜″ to 1⅞″ (35 to 47 mm). The forewing is long and somewhat pointed at the tip (apex). It is mostly tan with a peppering of dark scales. There is a gray line at the wing tip that extends diagonally inward less than half way across the wing, then becomes a line of black dots that continues to the inner margin. On some individuals, the triangular area beyond the gray line is tinted grayish. The discal cell is tinted reddish-orange from the base to the gray line. There are three noticeable horizontal lines; the antemedial (AM) line between the basal and median areas; the postmedial (PM) line that separates the median area from the postmedial area; and the terminal line at the outer margin. On some individuals, the AM line consists of a row of gray dots, one on each vein. On others, the AM line is absent. The PM line is a smoothly curved row of gray spots, one on each vein. The terminal line is a straight row of small gray spots. There is a circular spot in the median area (orbicular spot) and a kidney-shaped spot at the end of the discal cell (reniform spot). Both spots have broad pale border with a small center the same color as the background. On some individuals both spots inconspicuous or absent. There is no wedge-shaped spot near the inner margin (claviform spot). The cubital (Cu) vein is often white. There is always a small but conspicuous white spot at the outer (distal) end of the Cu vein), and often a small gray area just beyond the spot.

The hindwings are grayish-brown, pale at the base grading to dark at the tip. The veins and discal spot are dark.

The head and thorax are a similar color to the forewings but darker. On the upper side of the thorax there is a tuft of hairs that is dark just behind the head, otherwise the same color as the forewing. The antennae are threadlike on both the male and the female. The eyes are covered with fine hairs. The pair of small, finger-like processes (labial palps) curving up from the lower part of the head are long, extending at least to the middle of the face.

The caterpillar is up to 2″ long.

Leaves and sometimes seed heads of mostly grains and other grasses in the family Poaceae, but also many broadleaf plants close to their infestations.

Flower nectar

Adults are active at night and will come to light.

After defoliating a stand of plants, the larvae will move as a group to a nearby stand and resume feeding.

Sources: 21, 24, 29, 30, 71, 75.

Location: Woodbury, Minnesota