Armyworm Identification Guide
A striped, smooth-bodied caterpillar that moves in large groups across lawns and fields, most active after dark.
Read the full Armyworm encyclopedia entry →
Key Visual Features
Armyworms are smooth, hairless caterpillars typically growing to about 1.5 inches long.
- Color: Base color ranges from pale green to brown or nearly black depending on age
- Stripes: Several narrow, light-colored stripes run lengthwise down the body, often alternating with darker bands
- Head: Head capsule is usually brown to greenish with a pale, inverted "Y" or net-like pattern visible on the front
- Body shape: Cylindrical and tapered slightly at both ends, with no spines or hairy tufts
- Legs: Three pairs of true legs near the head plus fleshy prolegs along the rear half of the body
Where and When You'll See It
Armyworms are named for their habit of moving across lawns, pastures, and grain fields in large numbers, appearing almost overnight after hatching in dense clusters. They favor grasses, turf, corn, and small grains. Sightings peak in late spring through summer, particularly after warm, humid weather. Because they feed mainly at night and hide in thatch, soil, or leaf litter during the day, an armyworm outbreak is often noticed first through patches of closely chewed grass rather than the caterpillars themselves.
Similar-Looking Bugs
Armyworms are easily confused with several close relatives:
- Fall armyworm: Very similar striped pattern, but has four dark spots arranged in a square on the last body segment and a more pronounced pale "Y" on the head
- Cutworms: Thicker-bodied, often curl into a tight "C" shape when disturbed, and tend to stay below the soil surface rather than moving in groups
- Corn earworm: More variable in color with a spinier texture and is usually found singly inside corn ears rather than in groups on open turf
Quick ID Checklist
- Smooth, striped caterpillar around 1.5 inches long
- Pale, inverted Y-shaped mark on the head capsule
- Found moving in large groups across grass or crop fields
- Most active at night, hidden in thatch or soil by day
- No spines, horns, or hairy tufts on the body
Frequently asked questions
What does an armyworm caterpillar look like?
It is a smooth, striped caterpillar, usually green to brown, with a pale inverted Y-shaped mark on its head and several lengthwise stripes running down its body.
Why are they called armyworms?
The name comes from their behavior of moving across lawns and fields together in large numbers, as if marching in an army, once local food is stripped bare.
How can I tell an armyworm from a fall armyworm?
Look at the last body segment: fall armyworms have four dark spots arranged in a square there, which regular armyworms lack.
When are armyworms most likely to be seen?
They are most commonly noticed in late spring and summer, especially after warm, humid conditions, and are most active feeding at night.