Beet Armyworm (Spodoptera exigua) — identification, habitat & look-alikes

The beet armyworm is a small, drab gray-brown moth whose caterpillars feed on a huge range of plants, from beets, lettuce, and tomatoes to cotton, corn, and flowers. In the US it survives winter mainly in Arizona, Florida, and Texas, then spreads each year across the southern half of the country. Caterpillars strip leaves from small plants and bore into lettuce heads.

Appearance

Appearance: Adults have a wingspan of about 1–1¼ in (25–30 mm). The forewings are mottled gray and brown with irregular bands and a pale, bean-shaped spot; the hindwings are white to gray with a dark line along the edge.

Look-alikes

Southern armywormSpodoptera eridania

Beet armyworm caterpillars sometimes have a dark spot on the side of the body just behind the head, on the second segment of the thorax. Southern armyworms have their dark side spot farther back, on the first segment of the abdomen.

Why they get mixed upBoth are striped armyworm caterpillars that feed on the same vegetable crops in the South.

Where it lives

Typical habitats: Farm fields
Vegetable gardens
Greenhouses
Weedy fields
Range: Native to Asia, probably Southeast Asia, and now found almost wherever its food crops are grown. It reached North America around 1876 (first recorded in Oregon) and Florida in 1924.
Preferred conditions: It can't handle cold. Frost kills its food plants, so it overwinters only in warm areas and must re-invade other regions each year.

Behavior

Diet: Caterpillars eat many vegetable, field, and flower crops, including cotton, corn, soybeans, tomatoes, and lettuce. Weeds such as lambsquarters, pigweed, purslane, and Russian thistle also feed them, and pigweed was the best food in lab tests.
Activity: Caterpillars strip leaves from small plants, bore into lettuce heads and other produce, and leave silk webbing on leaves. Adults often fly in from nearby fields and weeds.

Life cycle

Breeding season: The whole life cycle can take as little as 24 days; in Florida, six generations have been raised in five summer months.
Clutch size: A female lays roughly 300–1,000 eggs, in clusters of 50–150 on the undersides of leaves, often near flowers and branch tips. Each cluster is covered with whitish scales that make it look fuzzy, like cotton.
Incubation: Two to three days in warm weather.
Larva: Caterpillars usually go through five stages. Young ones are pale green or yellow; older ones vary a lot, often green on top and pink or yellow below with a white side stripe, and some are almost black. They in the soil, and adults emerge in about a week.