Cabbage Worms is the common term used for the larvae of the **Cabbage White butterfly** (*Pieris rapae*), a common and destructive pest of plants in the mustard family (Brassicaceae). These worms are a major concern for home and commercial gardeners, as they feed voraciously on the leaves of cabbage, broccoli, cauliflower, kale, and Brussels sprouts, causing extensive defoliation and often boring into the heads of cabbages and cauliflowers, rendering them unmarketable.
Taxonomy and Classification
The Cabbage White butterfly, whose larvae are the Cabbage Worms, belongs to the family Pieridae (the whites and sulphurs) in the order Lepidoptera (moths and butterflies). It is a highly invasive species, native to Europe and Asia, and now established worldwide wherever its host plants grow. It undergoes complete metamorphosis (egg, larva/worm, pupa/chrysalis, adult).
Physical Description
The adult butterfly is small, typically white or yellowish-white, with two or three black spots on the forewings. It is often seen fluttering gracefully around garden plants. This seemingly harmless butterfly is the source of the destructive worm.
The **Cabbage Worm** larva is the key pest stage. It is a velvety green caterpillar, about 25–30 millimeters long when fully grown. It has a faint yellow or orange stripe running down its back. Its green color provides excellent camouflage against the host plant leaves. The pupa (chrysalis) is pale green or brownish and attaches to the plant or nearby structures.
Distribution and Habitat
The Cabbage Worm is a cosmopolitan pest found throughout the United States, Canada, and nearly all temperate and subtropical regions globally. Their habitat is specifically restricted to the host plants in the mustard family, *Brassica* species. They are prevalent in vegetable gardens, commercial fields, and wherever wild mustards or related weeds grow.
Behavior and Life Cycle
Cabbage Worms have multiple generations per year (three to five in temperate climates). The female butterfly lays distinctive, yellowish, cone-shaped eggs singly on the undersides of host plant leaves. This staggered egg-laying means multiple life stages are present simultaneously throughout the growing season.
The larva hatches and begins feeding immediately. It is active during the day and feeds voraciously for several weeks before pupating. The caterpillar overwinters in the chrysalis stage, often attached to plant debris or fence posts, emerging as a butterfly the following spring to start the cycle anew.
Feeding and Damage
Cabbage Worms feed almost exclusively on the leaves of cruciferous plants. Early feeding results in small, irregular holes, but as the larvae grow, they consume large, ragged sections of the leaf. They produce large amounts of dark green, soft **frass** (excrement) that often contaminates the leaves or the inner parts of the cabbage head.
The most serious damage occurs when the worms bore into the forming heads of cabbage or broccoli, making the produce unusable. Severe, unchecked defoliation can stunt or kill young plants, dramatically reducing yields and market quality.
Management and Prevention
Effective control is achieved through Integrated Pest Management (IPM), often relying on non-chemical methods. **Exclusion** is highly effective: covering plants with lightweight row covers or **fine netting** immediately after planting prevents the adults from laying eggs.
**Biological control** uses the bacterial insecticide **Bacillus thuringiensis (B.t.)**. This is a highly targeted control that only affects caterpillars when they ingest treated foliage and is safe for humans and beneficial insects. **Hand-picking** is feasible for small gardens, and destroying the yellow, cone-shaped eggs on the leaf undersides can also reduce populations. Controlling weedy members of the mustard family can eliminate secondary host sources.
Conservation and Research
While the Cabbage Worm is a pest, the butterfly is a common pollinator. Research focuses on increasing the efficiency of natural parasitic wasps, like *Cotesia glomerata*, which lay their eggs inside the worms. There is also ongoing research into developing plant varieties with genetic resistance to Cabbage Worm feeding.