Cutworms are the larval stage of several moth species belonging to the family Noctuidae, often called owlet moths. These pests undergo complete metamorphosis, transitioning through four phases: egg, larva, pupa, and adult. Understanding this cycle explains the appearance, behavior, and eventual fate of the cutworm.
The Starting Point: Egg Placement and Timing
The life cycle begins when the adult female moth lays eggs, usually during late summer, fall, or early spring, depending on the species and climate. Moths typically seek low-lying vegetation, such as grass blades, weeds, or plant stems, to deposit their eggs. Some species lay eggs singly, while others place them in clusters.
The eggs are initially white or pale yellow, darkening before the larvae hatch, which takes a few days to two weeks. In colder regions, many cutworm species overwinter in the soil either as eggs or as small larvae. Moths prefer laying eggs in areas with dense vegetation or abundant plant residue, which provides the newly hatched larvae with an immediate food source.
The Destructive Phase: Cutworm Larva
The stage recognized as the cutworm is the larva, a caterpillar that grows up to two inches long when fully developed. These larvae generally have a plump, smooth, and somewhat greasy appearance, with colors ranging from dull gray or brown to nearly black. When disturbed, they curl their bodies into a characteristic “C” shape.
They are named “cutworms” because they sever the stems of young plants at or just below the soil surface. They possess strong chewing mouthparts and can fell multiple seedlings in a single night. The cutworm is primarily nocturnal, hiding during the day in the soil, under debris, or within burrows near the base of the plant.
The larval stage lasts several weeks, often 28 to 35 days for common species like the black cutworm. During this time, the larva molts six or seven times as it grows larger. As they mature, the larvae become increasingly destructive, making early spring and early summer the peak time for plant damage. Once the larva reaches full size, feeding ceases, and it prepares for the next phase.
The Final Transformation: Pupa to Adult Moth
Once the larva is fully grown, it burrows deeper into the soil, usually a few inches below the surface, to begin the pupal stage. The larva constructs a small, smooth earthen chamber where it transforms into a pupa. The pupa is a dark brown casing, typically measuring between a half-inch to an inch long.
This is a non-feeding, dormant period that lasts from a few weeks to several months, depending on the species and the ambient temperature. For instance, black cutworm pupation may take about 12 to 15 days under favorable conditions. The pupa is the physical bridge that allows the caterpillar to reorganize its body structure into a completely different form.
The final transformation results in the emergence of the adult moth. These insects are medium-sized, stout-bodied moths with a wingspan of one to two inches. They are often called owlet moths or “millers” and typically display drab, camouflage coloration, such as shades of brown, gray, or black, with irregular patterns on their forewings.
Adult moths do not feed on plant stems or foliage and are harmless to garden plants. Their primary function is reproduction and dispersal. After emerging from the soil, the moths mate, and the females lay their eggs, starting the life cycle anew. This cycle may repeat multiple times in a single year, with some species producing three to seven generations in warmer climates.