What You Notice First Is Usually Not the Worm
Most people find cabbage worms because their brassicas suddenly look as if someone took a paper hole-punch to the leaves. The damage starts as tiny “windowpane” patches where the green tissue has been scraped away but the thin lower skin remains. A day or two later, those patches become ragged holes.
On kale, broccoli, cabbage, cauliflower, bok choy, Brussels sprouts, collards, and turnips, the culprit may be called a cabbage worm, but several different caterpillars cause nearly identical early damage. Correct identification matters because their hiding habits are different, and a quick glance at the top of a leaf often misses the real population.
The first thing I look for is not the hole. I turn over the leaf directly above it and look for fresh frass: small, damp-looking green or nearly black pellets. Fresh frass means the caterpillar is nearby, usually within a few inches. Old holes without frass may be damage from last week, after the caterpillar has already moved on or been eaten by a bird.
If you see holes but no fresh pellets, do not assume your plant is actively infested. Check new growth before treating anything.
The Three Caterpillars Most Gardeners Call Cabbage Worms
Imported cabbageworm: the soft green one that blends in
The imported cabbageworm is the classic cabbage caterpillar. It is velvety green, usually about 1 to 1.25 inches long when mature, and has a faint pale yellow line running down its back. It is plump but not chunky, with a smooth, almost matte surface.
This is the larva of the small white butterfly that flutters through vegetable gardens in daylight. If you have watched white butterflies bobbing around your kale or cabbage in late morning, imported cabbageworms are the most likely explanation.
They are particularly easy to miss on curly kale and inside cabbage leaves because their color is almost identical to the plant. Look along the leaf midrib, under overlapping leaves, and near the growing point. A mature worm may sit perfectly still until you touch the leaf.
Cabbage looper: the one that moves like an inchworm
Cabbage loopers are pale to medium green, longer and narrower than imported cabbageworms, and commonly reach 1.5 inches. They have thin white stripes along the sides. Their best identifying feature is how they walk: they pull the middle of the body up into a loop, then stretch forward. That looping motion is unmistakable.
Loopers tend to make larger irregular holes as they grow. They often feed on the broad outer leaves first, then move inward. On broccoli, they can disappear into the tight folds near the developing head, where they leave frass that is more annoying than the leaf damage itself.
Diamondback moth larvae: small, fast, and surprisingly destructive
Diamondback moth larvae are smaller, slender green caterpillars, often less than half an inch long when first noticed. They may have a slightly pointed rear end. When disturbed, they wiggle hard and often drop off the leaf on a thin silk thread.
These are easy to overlook because they feed in small numbers across many leaves. Instead of one giant hole, you may see dozens of tiny holes or translucent scraped patches. In warm weather, their population can build quickly.
A Realistic Check That Catches Most Infestations
One July morning, I found six broccoli plants with holes in only the newest leaves. From standing height, the plants looked fine. On the third plant, I turned over two leaves near the center and found fresh green pellets lodged where the leaf stems met. There were three small diamondback larvae, each only about a quarter inch long, and one larger imported cabbageworm tucked against the midrib.
The damage had appeared over roughly four days. The important clue was that the newest leaves were being hit. Older outer leaves had a few old holes, but the fresh frass and pale scrape marks near the center showed the feeding was current. Removing four caterpillars by hand that morning prevented them from reaching the broccoli heads a week later.
That is why a close inspection beats judging the situation by leaf damage alone.
How to Tell Worm Damage From Other Brassica Problems
Cabbage worms chew. Their damage has missing tissue, ragged edges, or translucent scraped areas. If the leaf is yellowing, curling, puckering, or covered in a sticky coating without obvious chewing, look for something else.
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Round or ragged holes with green pellets nearby: caterpillars are the likely cause.
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Many pin-sized “shot holes,” especially on seedlings: flea beetles are more likely. They are tiny jumping beetles, not worms.
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Leaves curled inward with clusters of gray-green insects: cabbage aphids.
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Leaf edges stripped overnight with shiny slime trails: slugs or snails.
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White butterfly activity during the day: inspect for imported cabbageworm eggs and larvae.
A common mistake is blaming every hole on cabbage worms and spraying immediately. Flea beetle damage on young arugula or bok choy will not be solved by a caterpillar treatment. Also, a plant can carry old worm damage for the rest of its life while continuing to produce perfectly good leaves.
Where the Eggs and Worms Hide
Check the underside of leaves first. Imported cabbageworm eggs are tiny, pale yellow to cream, upright, and shaped a little like miniature footballs. They are usually laid singly. Cabbage looper eggs are also pale and ridged, but they are often placed on the undersides of leaves and may be harder to spot.
Don’t spend ten minutes staring at every leaf surface. Work methodically: inspect the newest five leaves, then the undersides of two or three large outer leaves, then the tight center of the plant. On heading cabbage, gently separate the outer wrapper leaves. On broccoli and cauliflower, check where leaves curl around the developing head.
A quick five-minute inspection routine
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Look for fresh frass before looking for caterpillars.
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Turn over damaged leaves and trace inward toward newer growth.
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Check the midrib and leaf folds with your fingers.
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Watch for a caterpillar dropping on silk when the plant is bumped.
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Inspect twice a week while white butterflies or small brown moths are active.
When You Do Not Need to Fix It
A few holes in the oldest kale leaves are not an emergency. If you find one worm, remove it, inspect the plant again in three days, and carry on. Mature kale and collards can lose a noticeable amount of outer leaf tissue without affecting harvest. Even cabbage can tolerate minor feeding early in its growth.
The situation changes when fresh frass appears in the center of cabbage, inside broccoli crowns, or around cauliflower curds. At that point, the problem is less about plant health and more about harvesting food with caterpillars and droppings tucked into places that are difficult to wash.
The non-obvious part is that the cleanest-looking plant is not always the least infested. A caterpillar feeding deep in a broccoli head can leave little visible leaf damage while contaminating the part you intend to eat. Conversely, a kale plant with chewed outer leaves may have no active worms at all.
Practical Advice Once You Find Them
For a small garden, hand-picking is still the most reliable first response. Drop caterpillars into soapy water rather than tossing them onto the ground beside the bed; many simply crawl back. If you consistently find more than a few larvae per plant, use a product containing Bacillus thuringiensis var. kurstaki, usually labeled Bt or Btk, following the label exactly. It works when young caterpillars eat treated foliage, so spray leaf surfaces thoroughly, including undersides, and reapply after heavy rain if the label directs it.
For prevention, lightweight insect netting installed before butterflies arrive is far more effective than chasing worms after damage starts. Secure the edges tightly. A row cover with gaps is basically a welcome mat for moths.
Identify the feeding pattern, look for fresh frass, and inspect the plant’s center. Once you get used to that routine, cabbage worms stop feeling invisible—and they become one of the easier brassica pests to manage.
