A cutworm is the larval stage of a moth in the Noctuidae family, commonly called owlet moths. These caterpillars earn their name from their signature behavior: cutting down young plants by chewing through stems at or near the soil line. They’re one of the most frustrating garden pests because they feed at night and hide underground during the day, so you often discover the damage before you ever see the culprit.
How to Identify Cutworms
Cutworms are smooth, plump caterpillars that curl into a tight C-shape when disturbed. Most are dull gray, brown, or black, though some species have faint stripes or spots. They range from about half an inch when young to nearly two inches when fully grown. You’ll rarely spot them in daylight. They burrow into the top layer of soil or tuck themselves into cracks in the ground during the day, emerging after dark to feed.
The adult form is a drab, medium-sized moth with brownish or grayish wings. These moths are nocturnal, feeding on nectar and resting in grasses during the day. They lay eggs in soil, on low-growing weeds, or on plant debris, and the larvae that hatch are the cutworms that cause all the trouble.
Four Types of Cutworms
Not all cutworms behave the same way. They fall into four general categories based on how and where they feed:
- Surface cutworms are the most common type in home gardens. They chew through plant stems just above or just below the soil line, eating just enough to topple the plant. They sometimes drag plant parts down into their burrows.
- Climbing cutworms crawl up the stems of herbaceous plants, shrubs, vines, and even trees to feed on buds, leaves, and fruits.
- Army cutworms appear in large numbers and consume vegetation in one area before migrating by the thousands to adjacent land. They feed from the tops of plants and, in big enough groups, devour entire plants.
- Subterranean cutworms stay underground entirely, feeding on roots and the buried portions of stems.
Surface cutworms are responsible for the classic damage most gardeners recognize: seedlings that were healthy yesterday, now lying flat on the soil with their stems cleanly severed.
What Cutworm Damage Looks Like
The telltale sign is young plants cut off near ground level, with green stems bent over in the dirt. Sometimes a cutworm chews partway through a stem without severing it completely, leaving the plant wilting but still attached. Young larvae start by nibbling on leaves and small roots, but once they reach about half an inch long, they graduate to attacking stems by curling their bodies around them and chewing through.
Cutworms are most destructive to seedlings and fresh transplants in early to late spring. A single caterpillar can cut down several plants in one night, moving from stem to stem. Tomatoes, peppers, beans, lettuce, corn, and other tender young vegetables are all vulnerable, along with many flower seedlings. Established plants with thick, woody stems are generally safe.
Life Cycle and Timing
The complete development from egg to adult moth takes roughly 35 to 65 days, depending on species and temperature. The larval feeding stage, which is the window when they’re damaging your plants, lasts 20 to 40 days. During this period, the caterpillar goes through several growth stages, getting larger and more destructive with each one.
After the larval stage, cutworms pupate in the soil. The adult moths that emerge mate and lay eggs, starting the cycle again. In warmer climates, multiple generations can occur in a single growing season. In cooler regions, cutworms typically overwinter as larvae or pupae in the soil, resuming activity in spring when temperatures warm up and new seedlings appear.
How to Find Them
Because cutworms are nocturnal and hide during the day, scouting for them takes some effort. If you find freshly cut seedlings in the morning, dig gently in the top inch or two of soil around the damaged plant. You’ll often find the caterpillar curled up nearby. Going out after dark with a flashlight is another effective approach, since that’s when they’re actively feeding on the soil surface.
Protecting Your Plants
The simplest and most reliable defense is a physical barrier. Place a stiff cardboard collar, or a section of a cardboard tube, around each transplant stem at planting time. The collar should extend 1 inch above the soil surface and 2 inches below ground, with about half an inch of clearance around the stem. Toilet paper rolls cut in half or small cans with both ends removed work well. This blocks the caterpillar from wrapping around the stem.
Tilling the garden in fall or early spring exposes overwintering larvae and pupae to birds, cold, and drying out. Keeping the garden free of weeds and plant debris in early spring also removes egg-laying sites and food sources that support young larvae before your crops go in.
Biological Controls
Beneficial nematodes, specifically a species called Steinernema carpocapsae, can parasitize and kill cutworm larvae in the soil. These microscopic worms are applied as a soil drench and need adequate moisture to work. Research shows they’re significantly more effective when they’ve had time to rehydrate in moist soil before encountering cutworm larvae, so watering the area before and after application helps.
A bacterial spray called Bt (Bacillus thuringiensis) is another option, though it has limitations with cutworms. Bt works best against very young larvae in their earliest growth stages. It breaks down rapidly in sunlight and washes off leaves easily, so timing matters. It’s less effective against older, larger cutworms that are doing the most damage. If you use Bt, avoid irrigating for two days after application.
Handpicking
For small gardens, handpicking is surprisingly effective. Go out after dark with a flashlight, check the base of susceptible plants, and drop any cutworms you find into a bucket of soapy water. You can also dig around the base of freshly damaged plants during the day to find the caterpillar hiding just below the surface. It’s tedious, but a few nights of this during peak activity in spring can make a real difference.