The common garden pest known as the cabbage worm is the larval stage of a small, white butterfly. These small, destructive caterpillars are responsible for the ragged holes that appear in leaves seemingly overnight. This transformation is part of a complete biological life cycle.
Identifying the Cabbage Worm
The caterpillar stage, commonly called the imported cabbageworm, is known for its camouflage against host plants. This larva is velvety-green, reaching about an inch in length when fully grown. A faint yellow-orange stripe runs down the center of its back, helping it blend in with the leaf veins of cabbages and related plants. It is important to distinguish this caterpillar from the cabbage looper, which is more slender and moves with a distinctive “looping” motion. The imported cabbageworm is a straight crawler with dense, fine hairs.
The Adult Form: Butterfly or Moth?
The cabbage worm emerges as the Cabbage White butterfly, a member of the family Pieridae. The adult insect is small, featuring white or yellowish-white wings with a wingspan between 1.5 and 2.5 inches. Both sexes have black spots on their wings; the female typically displays two spots on each forewing while the male has only one. Cabbage White butterflies are active during the day. They are distinguished from moths because butterflies possess clubbed antennae, which have a bulbous tip.
Completing the Life Cycle
The insect follows a process of complete metamorphosis, which involves four distinct stages: egg, larva, pupa, and adult. The cycle begins when the adult female lays small, yellowish eggs, usually singly on the underside of host plant leaves. After four to eight days, the eggs hatch into the larval stage, the cabbage worm. The larva spends two to three weeks feeding voraciously, growing through five instars. Once fully grown, the caterpillar seeks a sheltered spot to transition into the pupal stage. It forms a chrysalis, an exposed pupa that may be green, yellow, or brown to match its surroundings. The pupal stage lasts one to two weeks, though the autumn generation will overwinter in the chrysalis to emerge the following spring. This rapid cycle allows for three to five overlapping generations to occur each year, meaning gardeners deal with the pest throughout the growing season.
The Impact on Gardens
Host Preference
The close association of the insect with gardens stems from the feeding habits of the caterpillar, which has a strong preference for plants in the Brassica family. This includes common crops like cabbage, kale, broccoli, cauliflower, and Brussels sprouts.
Damage Caused
The larvae feed on the foliage, often leaving behind large, ragged holes in the leaves. As the caterpillars grow, they tend to move toward the center of the plant, causing the most severe damage by boring into developing heads of cabbage or broccoli. Their presence is frequently confirmed not just by the holes, but also by the dark, wet pellets of excrement, known as frass, they leave scattered on the leaves. This feeding behavior provides the practical context for the common name “cabbage worm” and highlights its status as a significant agricultural pest.