The Cabbage White Caterpillar, the larval stage of the butterfly known scientifically as Pieris rapae, is one of the most widely recognized and common insect pests in gardens and agricultural fields worldwide. Often called the imported cabbageworm, this caterpillar is an herbivore with a highly specialized diet that centers almost exclusively on a single family of plants. Understanding what these velvety green larvae consume is the first step for managing their presence. Their feeding habits are rooted in a unique co-evolutionary relationship with their host plants, which dictates where the female butterflies lay their eggs and where the caterpillars will feed.
The Primary Diet: Cultivated Brassicas
The vast majority of the Cabbage White Caterpillar’s diet is comprised of plants belonging to the Brassicaceae family, commonly known as the mustard family. This family includes many popular cultivated vegetables, which is why the caterpillar is a notable garden threat. Their strong preference for these crops is chemically driven, resulting from a long history of co-evolution.
The specific cultivated plants targeted are collectively known as cole crops. The caterpillars consume the leaves of these plants, and in the case of head-forming varieties, they will bore directly into the developing heads. This feeding behavior is directly linked to chemical compounds called glucosinolates, which act as feeding stimulants.
Cole crops include:
- Cabbage
- Broccoli
- Cauliflower
- Kale
- Collard greens
- Brussels sprouts
For most insects, glucosinolates are toxic defense mechanisms, but the Pieris rapae caterpillar has evolved specialized gut enzymes to neutralize these chemicals. One specific glucosinolate, sinigrin, is believed to initiate the feeding process, while another, glucobrassin, is used by the adult female butterfly as a cue to confirm a suitable host for laying eggs. This chemical dependence explains why the caterpillars thrive almost exclusively on these plants.
Alternative and Weed Host Plants
While cultivated brassicas form the staple of their diet, Cabbage White Caterpillars will also feed on a range of related wild and ornamental plants, particularly when primary food sources are scarce or overcrowded. These secondary host plants are also members of the Brassicaceae family, sharing the same glucosinolate compounds that attract the caterpillars. The inclusion of these alternative hosts allows the species to persist in areas without commercial vegetable production.
Common examples of these secondary food sources include various wild mustards, such as charlock and hedge mustard, which grow readily in disturbed soil and field margins. Similarly, weeds like Shepherd’s purse and peppergrass can act as host plants, sustaining populations that can later move into nearby gardens. Certain ornamental flowers that are botanically related to the brassicas, such as nasturtiums and cleome, can also be utilized as food sources. Nasturtiums, in particular, are sometimes intentionally planted as a “trap crop” to divert the pests away from valuable vegetable plants.
Identifying Feeding Damage
Recognizing the specific damage caused by Cabbage White Caterpillars is the most effective way for gardeners to identify an infestation. The caterpillars feed by chewing large, irregular holes out of the leaves, a pattern of damage distinct from the scraping or skeletonizing done by other pests. This damage is often concentrated on the outer and lower leaves in the early stages of an infestation.
As the caterpillars grow, they tend to burrow toward the center of the plant, especially in forming heads of cabbage or broccoli. This deep feeding not only destroys the plant’s yield but also makes the pest difficult to spot.
A key indicator of their presence is the appearance of dark, greenish-brown fecal pellets, known as frass, scattered across the leaves or lodged in the crevices of the plant. The frass is essentially concentrated waste material and its presence confirms active feeding, even if the velvety green caterpillar itself is camouflaged along the leaf veins. Early instar larvae often feed near the midrib of the leaf, but as they mature, their appetite increases significantly, leading to severe defoliation. The combination of irregular holes and the presence of frass is a definitive sign that Pieris rapae is active.