The cabbage white caterpillar is the larval stage of the cabbage white butterfly (Pieris rapae), and it’s one of the most common pests in vegetable gardens. These velvety green caterpillars feed on cabbage, broccoli, cauliflower, Brussels sprouts, and other related crops, chewing large irregular holes through leaves and sometimes destroying developing heads entirely. If you’ve spotted small green worms on your brassicas or noticed ragged holes appearing overnight, this is almost certainly what you’re dealing with.
How to Identify Them
Cabbage white caterpillars are velvety green with a faint yellow stripe running down their back and a row of yellow spots along each side. At full size they reach about 30 mm (just over an inch) long. Their green color makes them surprisingly hard to spot against brassica leaves, especially when they’re young and small. Look along the central vein and upper leaf surfaces, where they tend to feed.
The eggs are easier to find if you know what to look for. They’re tiny, oblong, and white to cream colored, turning yellowish as they mature. Each egg stands upright on one end, sometimes described as shaped like a tiny football, and is laid individually on the underside of leaves. The adult butterflies that lay them are the familiar white butterflies with black wing tips you’ll see fluttering low over garden beds from spring through fall.
Life Cycle and Timing
Once an egg hatches, the caterpillar passes through five growth stages over roughly 15 days, shedding its skin between each one. After reaching full size, it pupates, a process that takes 11 days to a few weeks depending on temperature. In warm climates, multiple generations can cycle through a single growing season, which is why damage tends to get worse as summer progresses rather than tapering off.
This timing matters for control. The caterpillars are easiest to manage when they’re small and in their first few growth stages. By the time they’re large and burrowing into the center of a cabbage head, they’re harder to reach with sprays and have already done significant damage.
What the Damage Looks Like
Young caterpillars feed on the upper leaf surface near the midrib, producing large, irregular holes between the major veins. As they grow, they move toward the center of the plant and can strip leaves down to nothing but the main veins. Severe feeding stunts cabbage and cauliflower heads, and damage to developing buds on young cabbages can cause heads to abort completely, meaning the plant never forms a harvestable head at all.
Beyond the chewing itself, the caterpillars produce a large quantity of greenish-brown droppings (called frass) that accumulates on leaves and contaminates heads. Even if the feeding damage is modest, this contamination can make harvested produce unappetizing or unsaleable. Root crops in the brassica family, like rutabaga, generally suffer little meaningful damage.
Physical Barriers: The Most Reliable Prevention
The single most effective way to prevent cabbage white caterpillars is stopping the butterfly from reaching your plants in the first place. Floating row covers and insect netting do this well. The key is installing them immediately after transplanting or as soon as seedlings emerge, and securing the edges tightly to the ground with landscape staples, boards, bricks, or soil. Any gap is an invitation.
Lightweight row cover (around 0.45 ounces per square yard) lets through 90 to 95 percent of light and provides a couple degrees of frost protection, making it suitable to leave on crops from planting through harvest. In summer, when heat buildup under row cover becomes a problem, insect netting made from polyethylene is a better choice. It’s see-through, breathable, and available in mesh sizes small enough to exclude even tiny pests. You can drape the fabric directly over plants or build simple support frames from PVC pipe, wire, or wood to keep it elevated.
Bt Spray: A Targeted Organic Option
If caterpillars are already on your plants, the most widely used organic treatment is a spray containing Bt (Bacillus thuringiensis var. kurstaki). This is a naturally occurring soil bacterium that produces proteins toxic specifically to caterpillars. When a caterpillar eats treated leaves, the proteins paralyze its digestive system. It stops feeding within hours and dies from starvation over the following days.
Bt is safe for humans, pets, bees, and beneficial insects because it only affects caterpillars that ingest it. That specificity comes with a tradeoff: coverage must be thorough, since any untreated leaf surface is unprotected. It also breaks down on foliage in less than a week, so repeat applications are necessary, particularly after rain. Bt works best against younger, smaller caterpillars, so timing applications early is more effective than waiting until caterpillars are large.
Natural Enemies That Help
Cabbage white caterpillars have a powerful natural enemy: a tiny parasitoid wasp called Cotesia glomerata. These dark wasps are only 3 to 7 mm long and resemble small flying ants. A female wasp lays 20 to 60 eggs inside a young caterpillar’s body. The wasp larvae develop inside the caterpillar over 15 to 20 days, then emerge and spin small cocoons on or near the host, which dies. You may have seen clusters of 20 to 30 tiny yellowish cocoons near a dead caterpillar in your garden. That’s Cotesia at work.
Parasitism rates start low in early spring but climb steadily. By midseason, roughly half of cabbage white caterpillars are parasitized, and by late in the growing season that figure reaches 60 to 75 percent. This is one reason late-season caterpillar problems sometimes seem to resolve on their own.
To support these wasps, maintain some non-crop habitat around your garden edges and plant flowering species that provide nectar and pollen. The wasps are sensitive to extreme heat and die rapidly when temperatures exceed 90°F, so shaded refuge areas help them survive hot spells. Dill, borage, and other umbel-type flowers are particularly good at attracting parasitoid wasps and hoverflies to your garden.
Companion Planting and Trap Crops
Interplanting your brassicas with plants from different families can create what gardeners call “confusion planting.” The idea is that mixing visual and scent signals makes it harder for the butterfly to locate its target crop. Beets, chard, and other non-brassica vegetables planted among your cabbages and broccoli add this kind of diversity.
Nasturtiums serve a different role. Cabbage white butterflies are strongly attracted to them, so planting nasturtiums near your brassicas can act as a trap crop, drawing caterpillars to the nasturtiums instead of your vegetables. Some gardeners plant them directly beneath broccoli or kale plants, where caterpillars feed on the nasturtiums rather than climbing up the stems of the crop above.
Companion planting alone won’t eliminate the problem, but combined with physical barriers, Bt sprays when needed, and habitat for parasitoid wasps, it adds another layer of protection. Most gardeners who successfully manage cabbage white caterpillars without synthetic pesticides use several of these strategies together rather than relying on any single one.
Hand Picking: Simple but Effective
For small gardens, hand removal works surprisingly well. Check the undersides of leaves for eggs every few days and crush or remove them before they hatch. Inspect along the central leaf vein and near the growing point of the plant for caterpillars, remembering that their green color camouflages them effectively. The frass they leave behind is often easier to spot than the caterpillars themselves: small greenish-brown pellets concentrated near feeding sites. Follow the droppings and you’ll find the culprit.