Cutworms are not true worms but the larval stage of several species of nocturnal moths. These plump, smooth-skinned caterpillars are among the most destructive early-season pests, primarily because their feeding habits target the most vulnerable part of a plant. They earn their name by physically severing young plant stems, often wiping out newly emerged seedlings and transplants overnight. Understanding the specific visual cues of their feeding is the first step in protecting a garden or field from widespread damage.
The Signature Symptom: Severed Seedlings
The most recognizable sign of cutworm activity is a young plant that has been cleanly clipped at or just below the soil surface. This damage typically appears suddenly in the morning, with the fallen plant lying near the remaining stem stump. This precise, surgical-like severance is the defining hallmark of surface-feeding cutworm species, such as the black cutworm, which operate exclusively at ground level.
The destructive mechanism involves the larva curling its body around the tender stem of a seedling. Once coiled, the cutworm chews through the tissue, completely separating the above-ground foliage from the root system. A single larva can destroy multiple seedlings in one night.
In some instances, damage occurs just below the soil line, resulting in the plant top disappearing entirely or a wilted stem stump that is not completely severed. The larva may then attempt to pull the severed plant part into its burrow for consumption during the day. This cutting is most common during early spring when plants are small and their stems are soft. Seedlings and recent transplants are particularly susceptible because their structural tissue is not yet hardened.
Damage to Mature Plants and Subsurface Areas
While cutting young stems is the most dramatic evidence, cutworms also inflict damage on larger, established plants through different feeding behaviors. Some species, known as climbing cutworms, ascend the plant at night instead of remaining near the soil surface. The variegated cutworm is a well-known example, climbing to feed on leaves, buds, and fruits.
This above-ground feeding results in irregular holes chewed into foliage, buds that fail to develop, or blemishes on fruits like tomatoes and peppers. This damage can sometimes be confused with that caused by other caterpillars, but the sign is the discovery of the plump, smooth larva on the plant stem at dusk or early morning.
Other species, referred to as subterranean cutworms, never venture above the soil line and focus their feeding entirely on underground plant parts. The glassy cutworm is a type that feeds primarily on roots and the underground parts of stems. This root feeding can lead to wilting in larger plants, as the damaged root system is unable to take up sufficient water. On root crops like potatoes or carrots, subterranean cutworms create shallow, irregular gouges or cavities directly into the vegetable tissue.
Confirming the Culprit and Eliminating Look-Alikes
Definitive identification requires confirming the presence of the larva itself, as other animals can cause similar-looking plant loss. Cutworms are generally smooth, hairless caterpillars ranging from one to two inches in length when fully grown. Their color varies by species, often appearing dull gray, brown, tan, or nearly black, sometimes with subtle spots or stripes running lengthwise.
The most reliable confirmation is their characteristic defensive posture: when disturbed, a cutworm will instantly curl its body into a tight “C” shape or a ball. To locate a surface-feeding cutworm, one must gently dig just an inch or two into the soil within a six-inch radius of the damaged plant stump. Since they are nocturnal, they hide in the soil or under debris during the day, making early morning the optimal time to search before they burrow deeper.
The clean, precise cut of a seedling distinguishes cutworm damage from other pests that might clip a plant. Slugs leave a silvery slime trail and cause irregular, ragged chewing damage, not a clean severance. Larger herbivores, like rabbits or deer, also cut plants, but their cuts are typically jagged and occur on thicker stems. The combination of the specific damage pattern and the presence of the curled, smooth larva confirms a cutworm infestation.