Cutworms and armyworms are closely related caterpillars that cause similar-looking damage to lawns, gardens, and crops, but they differ in key ways: how they feed, how they move, and the patterns of destruction they leave behind. Both are larvae of nocturnal moths in the same family, and both hide in soil or thatch during the day and feed at night. The practical distinction that matters most is that armyworms feed in groups and can sweep across a lawn or field in waves, while cutworms are typically solitary feeders that cause scattered, isolated damage.
How to Tell Them Apart
Armyworm and cutworm caterpillars look similar at first glance. Both range from light green to brown or nearly black, and both can reach about 1½ inches long at maturity. But a few reliable markings help you distinguish them.
Fall armyworm larvae have an inverted “Y” marking on the head capsule and four black dots arranged in a square pattern near the tail end of the body. They often have white lines running along the length of the body. These features are consistent enough to serve as a field ID even when coloring varies between individuals.
Cutworms are generally plumper, smoother-skinned caterpillars that curl into a C-shape when disturbed. They lack the distinctive head markings of armyworms. Many cutworm species are dull gray or brown, blending well with soil. If you find a caterpillar curled up just below the soil surface next to a seedling that’s been clipped at the base, you’re almost certainly looking at a cutworm.
Feeding Behavior and Damage Patterns
This is where the two pests diverge most clearly. Cutworms are solitary feeders. A single larva will settle near a plant, hide in the soil during the day, and emerge at night to chew through stems at or just below the soil line. The result is individual plants toppled over as if snipped with scissors. In lawns, cutworm damage appears as circular spots of dead grass or small depressed areas, often near aeration holes that larvae use as burrows.
Armyworms behave very differently. Their eggs are laid in masses, and the larvae hatch and feed as a group. When populations grow large and food runs low, they march together across the landscape, eating nearly everything in their path. This mass movement is what gives them their name. The damage from armyworms tends to be broad and fast-moving: you might notice a section of lawn or a strip of field crops being devoured seemingly overnight, with the front edge of damage advancing each day. Armyworms prefer damp areas, and their moths seek out moist spots near stressed plants to lay eggs.
Both types feed on leaves and crowns and can clip plants near the soil surface. But the pattern tells you which pest you have: scattered dead spots suggest cutworms, while a rapidly expanding swath of defoliation points to armyworms. One exception worth noting is the variegated cutworm, which can occasionally march in groups like armyworms when populations spike.
What They Attack
Armyworms primarily target grasses, small grains, and corn. They also attack alfalfa, beans, clover, flax, millet, and sugar beets. Their moths lay eggs at night in folded leaves or under the leaf sheaths of grain plants and grasses, gravitating toward lodged or wind-damaged stands where moisture and shade are abundant.
Cutworms have a broader appetite. The army cutworm, for example, feeds on cereal crops (especially winter wheat) but will also hit alfalfa, barley, canola, field corn, flax, mustard, oats, sugar beets, garden vegetables, various weeds, and grasses. If you’re growing it, a cutworm will probably eat it. This wide host range makes cutworms a more unpredictable garden pest, since they don’t limit themselves to one plant family.
Seasonal Timing
Both pests are active from roughly mid-March through October, but they show up at different points in the growing season. Army cutworms are primarily an early-season pest. In the northern Great Plains, they cause the most trouble in spring on winter wheat and other cereals that have been growing since fall. Armyworms, by contrast, tend to be a mid- to late-season problem. Their moths migrate northward on storm fronts in summer, and outbreaks often follow periods of cool, wet weather that favor egg-laying.
This timing difference matters for scouting. Early-season seedling losses in a vegetable garden or young crop field are more likely cutworm damage. Midsummer defoliation of established grass, corn, or small grains is more characteristic of armyworms.
When Damage Warrants Action
Not every caterpillar sighting means you need to intervene. Healthy, vigorously growing turf can tolerate moderate infestations of either pest. In field crops, established thresholds help guide decisions. For armyworms in corn, treatment is generally warranted when 25% of plants have two or more larvae, or 75% of plants have at least one. In wheat, the threshold is about three armyworms per square foot. These thresholds apply to larvae that are ¾ inch or smaller. Once caterpillars reach an inch in length, they’re close to pupating and nearly done feeding, so spraying at that point is a waste.
For lawns and gardens, the judgment call is more visual. If you’re seeing rapidly expanding dead patches and finding multiple caterpillars per square foot when you peel back the turf, control is reasonable.
Managing Both Pests
The good news is that cutworms and armyworms respond to the same control strategies, so you don’t need a precise ID before taking action.
Cultural controls come first. Remove thatch, overgrown areas, and lodged grass to eliminate the daytime hiding spots larvae depend on. Avoid overwatering, since armyworm moths seek out moist areas for egg-laying. Proper fertilization and irrigation keep turf vigorous enough to outgrow moderate feeding damage without any chemical intervention.
Natural enemies do significant work against both pests. Birds, parasitic wasps and flies, fungi, bacteria, and nematodes all suppress caterpillar populations. Beneficial nematodes (specifically the species Steinernema carpocapsae) can be applied to lawns in early morning or evening as a biological control option. You’ll need to water the lawn before and after application so the nematodes can move down into the thatch layer where larvae hide, and multiple applications may be necessary.
If you reach for an insecticide, spot-treat the infested area rather than blanketing the entire lawn or field. Mow first to remove any flowering weeds, which helps protect bees and other pollinators. Apply in the evening, since that’s when caterpillars emerge from their daytime resting spots and will have the most contact with the treatment. Any product labeled for lawn insect control will work on both armyworms and cutworms.
Quick Comparison
- Feeding style: Cutworms feed alone; armyworms feed in groups and march when food runs out.
- Damage pattern: Cutworms create isolated dead spots and clipped seedlings; armyworms create broad, fast-moving swaths of defoliation.
- Identification: Armyworms have an inverted Y on the head and four dots near the tail; cutworms are plumper, plain-colored, and curl into a C-shape.
- Host plants: Armyworms favor grasses and grains; cutworms eat nearly anything.
- Season: Cutworms cause the most trouble in early spring; armyworms peak in mid- to late summer.
- Location: Cutworms burrow into soil; armyworms rest in thatch but stay closer to the surface.