If you are staring at chewed cabbage leaves, ragged holes in kale, or tiny green caterpillars hiding under broccoli leaves, you are dealing with the insects people mean when they ask what are cabbage worms. These pests feed fast on brassicas and can strip a healthy planting in days if you ignore them. The good news is that they are easy to identify, and once you know what eats cabbage worms and what kills cabbage worms, you can get them under control without guessing.
What Cabbage Worms Are and Why They Show Up
Cabbage worms are the larval stage of several moths and butterflies that feed on brassica plants, including cabbage, broccoli, cauliflower, kale, collards, Brussels sprouts, and bok choy. The most common types in home gardens are imported cabbage worms, cabbage loopers, and diamondback moth larvae. The adults lay eggs on the undersides of leaves, and the hatching larvae start feeding right away.
They show up when host plants are available, especially in warm weather. A few larvae are easy to miss because they blend into leaves, but they can multiply fast. The damage starts as small holes, then becomes large ragged patches, skeletonized leaves, and contamination from green droppings on the plant.
How to Identify Cabbage Worm Damage
What the plant damage looks like
The clearest sign is irregular chewing on the leaves. Young plants lose whole sections of tissue, while larger plants show holes and scraped-looking areas between leaf veins. On cabbage and lettuce-like brassicas, larvae hide deep in the folded leaves, so the damage can be worse than it first appears.
Look for dark green or black pellets on leaves and stems. Those droppings, called frass, confirm active feeding. You may also find eggs on the undersides of leaves, usually laid singly or in small groups.
How the larvae differ
Cabbage worm is a broad garden term, and the larvae are not all the same. Imported cabbage worm larvae are velvety green and move sluggishly. Cabbage loopers arch their bodies as they crawl, like an inchworm. Diamondback moth larvae are small, light green, and active when disturbed.
All of them eat brassicas, and all of them leave the same kind of damage. If you see chewing on cabbage-family crops, treat the plant as a cabbage worm problem even if the exact species is unclear.
What Eats Cabbage Worms
Beneficial insects and birds help reduce cabbage worms, but they do not clear an infestation by themselves. Parasitoid wasps are the most important natural enemy. They lay eggs inside the larvae, and the developing wasps kill them. Lady beetles, lacewings, spiders, assassin bugs, and ground beetles also feed on eggs and small larvae.
Birds, especially chickadees, sparrows, and wrens, pick off caterpillars exposed on leaves. Toads and small lizards do the same in protected garden beds. If you want these helpers to stay, avoid broad-spectrum insecticides and keep a mix of flowering plants nearby for adult beneficial insects.
What Kills Cabbage Worms
Best home-garden treatments
Bacillus thuringiensis var. kurstaki, sold as Bt, is the most effective product for cabbage worms and loopers. It kills caterpillars that eat treated leaves, and it leaves beneficial insects alone if you apply it only to brassicas. Spray the tops and undersides of leaves until evenly coated, then reapply after rain and every 5 to 7 days while feeding continues.
Spinosad also kills cabbage worms and works well when infestations are heavier. Use it in the evening, coat the leaf surfaces, and follow the label for timing before harvest. Insecticidal soap does not solve this problem because it does not kill chewing caterpillars. Hand-picking works well on small plantings, especially early in the season.
A simple control plan that works
- Inspect the undersides of brassica leaves every 2 to 3 days.
- Remove eggs and pick off visible larvae by hand.
- Spray Bt on all brassica foliage at the first sign of fresh chewing.
- Repeat Bt after rain and at 5 to 7 day intervals while larvae are active.
- Switch to spinosad if the infestation is heavy and feeding continues.
- Cover plants with fine insect netting to keep adults from laying new eggs.
How to Prevent New Infestations
Row covers or insect netting stop moths and butterflies from laying eggs on your plants. Put the covers on right after transplanting or as soon as seedlings emerge, and seal the edges so insects cannot get underneath. This is the strongest prevention method for home gardens.
Keep brassica beds weed free, since mustard family weeds can feed the same pests. Rotate brassicas to a different part of the garden each season, and do not leave old crop debris in the bed after harvest. If you grow only a few plants, inspect them twice a week during warm weather and act at the first sign of eggs or chewing.
When to Worry About the Damage
Act fast when larvae are feeding on seedlings, heading cabbage, or tight broccoli florets. Young plants can be stunted quickly, and caterpillars that get into a cabbage head or broccoli crown are hard to remove cleanly. A few holes in mature kale are less serious, but the infestation still spreads if you leave it alone.
If leaves are heavily skeletonized, the crop is already under pressure and needs treatment the same day. The earlier you start Bt or hand removal, the less damage the plant takes and the less likely the pests are to keep cycling through the garden.
Frequently Asked Questions
Are cabbage worms harmful to people?
No. They do not bite people, sting, or spread disease. They are plant pests, not human pests. The issue is crop damage, not personal safety.
Can I eat vegetables with cabbage worm damage?
Yes, after washing and trimming damaged areas. Remove the larvae, rinse the produce well, and cut away chewed or soiled sections. If caterpillars have been inside a tight cabbage head, separate the leaves and wash thoroughly before cooking or serving.
Does vinegar kill cabbage worms?
No. Vinegar does not reliably kill cabbage worms and can damage plant tissue. Use Bt, spinosad, hand-picking, and row covers instead.
Why do cabbage worms keep coming back?
Adult moths and butterflies keep laying eggs on brassicas as long as the plants are exposed. If you do not use covers and repeat treatments, new larvae hatch and start feeding again. Consistent inspection and prevention stop the cycle.