Cabbage worms
When gardeners say "cabbage worms" they usually mean the imported cabbageworm, Pieris rapae. It is the caterpillar of the small white (cabbage white) butterfly, the white butterfly with black wing tips that flits over brassicas on sunny days. The caterpillars are velvety green and slow-moving, and they lie along the leaf veins where they are hard to see. They chew large ragged holes, bore into cabbage and broccoli heads, and leave green frass behind. Kentucky Extension notes that different cabbage caterpillars may respond to different insecticides, so identify the species before you spray. This one is easy to kill with Bt while it is small. Row covers stop the butterflies laying eggs in the first place.
A late-instar Pieris rapae larva lying along the midrib of a cabbage leaf, with frass below. Photo: pending.
Identification
The caterpillar is green and velvety, because it is covered in fine short hairs, and it has prolegs along the whole abdomen (UF/IFAS counts five pairs). Full-grown larvae reach about 1 inch (UC IPM) to 1¼ inches (Kentucky), and UF/IFAS measured 30 mm. From the second instar on, a narrow yellow line runs down the centre of the back, with a broken yellow line or a row of yellow spots along each side. It moves slowly, rests along the midrib or a main vein, and matches the leaf so closely that it is easy to miss.
Telling it from the cabbage looper: the looper is smooth rather than velvety, pale green with white lines along its sides, and grows larger, 1½–2 inches. It has no legs in the middle of its body, so it arches into a loop as it walks, and the adult is a grey-brown moth that flies at night. The cabbageworm crawls flat, and its adult is the white butterfly you see by day. Two other brassica caterpillars differ again. The diamondback moth caterpillar is under ½ inch and wriggles violently when touched. The cross-striped cabbageworm is bluish-grey with black bands across its back and feeds in groups.
The adult is a white butterfly with black forewing tips. Females have two black spots on each forewing and males have one. The undersides of the wings are yellowish. Published sizes vary: a wingspan of 1½ inches (UC IPM) or 1.8–2.6 inches (4.5–6.5 cm, UF/IFAS), and about 1¾ inches (Kentucky). The eggs are bullet-shaped, ridged, and laid singly, standing on end, usually under the outer leaves, though they can turn up anywhere on the plant. UF/IFAS measured them at 1 mm tall; UMass gives about ⅛ inch. They start pale white and turn yellow.
Easily confused with
- Cabbage looperAlso a pestSmooth, pale green with white lines along the sides, and no legs in the middle of the body: it walks by arching its middle into a loop, like an inchworm.
- Diamondback moth caterpillarAlso a pestUnder ½ inch when full grown, pointed at both ends with a forked tail. Touch it and it wriggles violently and may drop off the leaf on a silk thread.
- Cross-striped cabbagewormAlso a pestBluish-grey on top with many black bands across the back and a yellow line down each side, and several feed together on one plant.
Damage symptoms
The caterpillars feed between the large veins, making large irregular holes. Left alone, they can reduce mature plants to stems and main veins. Older larvae move towards the centre of the plant and bore into cabbage and broccoli heads. Feeding on the developing bud of a young cabbage can make the head abort, according to Wisconsin Extension. The copious green-brown frass stains and contaminates the heads. Because the larvae cling tightly, they are easily missed when produce is washed.
- Large, ragged holes between the leaf veins, starting on the outer leaves
- Wet green frass pellets at the leaf bases and packed into heads
- Caterpillars inside broccoli and cabbage heads at harvest
- Leaves stripped to the main veins on heavily infested plants
- Stunted or aborted heads on young cabbage and cauliflower
- White butterflies with black wing tips visiting the crop by day
Lifecycle & degree days
The chrysalis spends the winter on plant debris, and the butterflies emerge in spring to lay eggs on wild mustards and early cole crops. One generation takes three to six weeks, depending on the weather. The number of generations rises from north to south: two to three in Canada, three in Wisconsin and three to four in central New England, three to five in California, and six to eight in the South. In Florida it can be found all year. In Wisconsin the second generation, from mid-July, does the most damage, because its larvae develop almost entirely on cultivated cole crops.
- Overwinters
- Chrysalis, on plant debris
- Egg to adult
- 3–6 weeks, by weather
- Generations / yr
- 2–3 Canada; 3 Wisconsin; 3–4 New England; 3–5 California; 6–8 South
- Larval feeding
- About 15 days in August (range 11–33)
- Pupa (summer)
- About 11 days
Host crops
The imported cabbageworm feeds on the cabbage family and occasionally on other plants that contain mustard oils, such as nasturtium and sweet alyssum. UF/IFAS finds that cabbage, collards, Brussels sprouts, broccoli and cauliflower are preferred over Chinese cabbage, turnip, mustard, rutabaga and kale. The butterflies avoid laying eggs on red cabbage, although the larvae survive better on it. Dark green, glossy varieties resist cabbageworm but suffer more flea beetle damage. In the UK the same insect is the small white, one of several cabbage whites.
Monitoring & action thresholds
Commercial thresholds count the share of plants carrying any caterpillar, and they vary by source and crop stage. UMass treats cabbage, broccoli and cauliflower at 35% of plants infested before heads begin, cabbage and broccoli at 15% from head formation (15–20% in its 2022 sheet), 10% for cauliflower after heading, and 10–15% for kale and collards. It says spraying at those levels gave 98–100% clean heads, the same result as weekly sprays with far fewer applications. Wisconsin's figures differ: 10% in the seedbed; for cabbage, 30% from transplant to cupping, 20% from cupping to early heading and 10% from early heading to harvest; for broccoli and cauliflower, 50% from transplant to first flower or curd, then 10%. In a garden, look hardest as heads start to form, and for leafy greens earlier, since every leaf is eaten.
Start looking as soon as you see the white butterflies (Kentucky). Turn over the outer leaves and check along the midrib for eggs and small caterpillars. The feeding holes and frass are often easier to spot first, and then you can find the caterpillar. Check broccoli and cabbage plantings as they begin to form heads, and check kale, collards and other greens earlier, because all their leaves are harvested.
Biological control
Imported cabbageworm has a lot of natural enemies. The braconid wasp Cotesia glomerata (formerly Apanteles glomeratus) attacks young caterpillars; its larvae emerge from the mature caterpillar and spin a cluster of 20–30 cocoons beside it. In Massachusetts it has been largely replaced by Cotesia rubecula, which was introduced from China in 1988. Surveys in 2007 and 2009 found it at every site sampled, with an average of 75% parasitism. Other natural enemies include tachinid flies (more important than the wasps in some areas), the pupal parasitoid Pteromalus puparum, Trichogramma egg wasps, vespid wasps, predatory stink bugs, ambush bugs and birds. A granulosis virus can kill over 90% of larvae when numbers are high: infected caterpillars turn pale, then yellow and bloated. Bt kills small larvae and spares the parasitoids.
Cultural controls
In a home garden, keeping the butterflies off does more than anything sprayed afterwards.
- Cover brassicas with fine netting or floating row cover from planting, and keep it off the leaves so butterflies cannot lay through it
- Pick off caterpillars and crush the single yellow eggs under the leaves, or knock caterpillars into soapy water
- Leave caterpillars with clusters of small cocoons beside them — those are wasp cocoons, and the caterpillar is already dying
- Start transplants from seed or check bought ones for eggs and larvae
- Clear crop debris in autumn, or dig it in during spring, to remove overwintering chrysalises
- Soak harvested broccoli and cabbage and check the heads, as clinging larvae are easily missed
Chemical, last resort
- Bt kurstakiREI 4 h
- MethoxyfenozideREI 4 h
- SpinosadREI 4 h
- ChlorantraniliproleREI 4 h
Sources
UF/IFAS EDIS EENY-126/IN283, Imported Cabbageworm, Pieris rapae (Capinera)
UC IPM Pest Management Guidelines: Cole Crops — Imported Cabbageworm (Natwick et al., 12/20)
UC IPM, Relative Toxicities of Insecticides Used in Cole Crops to Natural Enemies
Univ. of Kentucky ENTFACT-300, Cabbage Pests (Bessin, rev. 1/26)
UMass Extension Vegetable Program, Imported Cabbageworm (2013)
UMass Extension, Caterpillars in Brassica Crops (Hazzard, Scheufele & McKeag, 2022)
UW–Madison Extension XHT1032, Imported Cabbageworm (Liesch & Groves, 2026)
RHS Advice, Cabbage caterpillars
Bonide Thuricide concentrate label, EPA Reg. 4-226 (2016)
DiPel DF label, EPA Reg. 73049-39 (2022)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Cabbage worms by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.