The imported cabbageworm is the most common of the green caterpillars that gardeners lump together as cabbage worms, alongside the cabbage looper and the diamondback moth larva. The early warning is the adult: a white butterfly with one or two black spots on each wing, fluttering over the garden on sunny days. It lays single, bullet-shaped yellow eggs on the leaves, and the hatching caterpillars are velvety green with a faint yellow stripe, often resting motionless along a leaf vein where their color hides them well.
How to identify an imported cabbageworm
Identification is satisfying and helps you scout, but the practical controls overlap heavily with the other brassica caterpillars, so do not let it slow your response.
The velvety body and normal crawl separate it from the smooth, looping cabbage looper. The white butterfly overhead is the clearest early sign, since you will usually see the adults before you find the caterpillars. For the full side-by-side picture and the shared toolkit, see the combined cabbage worms guide.
What it does and why early scouting wins
Young cabbageworms feed on the undersides of outer leaves, which brassicas tolerate well. The trouble starts as they grow and move toward the growing point and into developing heads, where they feed in protected folds and leave frass that fouls the harvest. Catching them while small, and before they reach the head, is far easier than digging them out of a dense cabbage later. Because the white butterflies lay eggs all season, a single planting can face several overlapping generations.
How to control imported cabbageworms, step by step
The plan
Cover from transplant
Put a floating row cover over the bed at transplant. Brassicas need no insect pollination, so the cover can stay on the entire crop, blocking the white butterflies from laying eggs.
Scout leaf undersides
Check under leaves and along veins every few days, focusing on the growing point and developing heads. Look for the bullet-shaped eggs, frass, and chewed edges.
Hand-pick what you find
Pull caterpillars and squash any eggs you find. The green camouflage is good, so let the frass and damage guide your eyes.
Use BT for outbreaks
A BT-based biological caterpillar control sprayed on the foliage handles heavy infestations and spares beneficial insects. Cover leaf undersides and reapply after rain.
Clean up after harvest
Remove old brassica stalks and leaves where pupae shelter, to reduce next season's pressure.
Row cover is the cleanest defense for brassicas
Brassicas are an ideal crop for season-long row cover because they set their edible parts without insect pollination. A floating row cover over hoops from transplant onward keeps the egg-laying butterflies off entirely, which is far easier than fighting caterpillars in a dense head later.
Hand-picking and BT for what gets through
If butterflies got in before you covered, or you are growing uncovered, hand-picking plus a BT spray covers the rest. Gloves keep your hands clean while you part dense leaves and pick caterpillars and eggs from the growing points.
For pressure beyond what hand-picking can handle, a BT-based biological control is the standard organic option. It is a naturally occurring soil bacterium that affects only caterpillars that eat treated leaves, so it spares bees, ladybugs, and other beneficial insects. Spray the foliage the caterpillars are eating, including leaf undersides, reapply after rain, and apply in the evening to protect pollinators. We are describing the approach generally rather than recommending a specific product.
Which plants get hit, and how to plan
The whole cabbage family is on the menu. Cabbage, broccoli, and cauliflower are favorites, with caterpillars boring into heads, and kale, collards, and Brussels sprouts are heavily attacked on the leaves. Leafy brassicas tolerate outer-leaf damage well, so focus your effort on protecting the parts you harvest.
Timing helps you stay ahead of the butterflies, which are active through the warm months. Use the planting calendar for your ZIP to schedule spring and fall brassica plantings, and remember that a fall crop maturing in cool weather often faces lighter caterpillar pressure. Knowing your frost dates lets you time that fall planting so it heads up before hard freezes while dodging peak summer butterfly activity.
What is the difference between an imported cabbageworm and a cabbage looper?
Both are green caterpillars on brassicas, but they look and move differently. The imported cabbageworm is velvety and fuzzy, crawls normally, and is the larva of the white butterfly with black wing spots. The cabbage looper is smooth and arches its back into a loop as it inches along, like an inchworm, and is the larva of a brown night-flying moth. A third pest, the diamondback moth larva, is smaller and wriggles when disturbed. The controls are the same for all three.
Can I leave a row cover on cabbage and broccoli all season?
Yes. Brassicas like cabbage, broccoli, kale, and collards do not need insect pollination for the parts you eat, so you can keep the cover on the whole crop. That makes exclusion the most effective single tactic against the imported cabbageworm, because it stops the white butterflies from ever laying eggs. Just seal the edges so adults cannot get underneath.
Is it safe to eat brassicas treated with BT?
BT-based caterpillar controls are widely used in organic vegetable growing and affect only caterpillars that eat treated foliage, sparing bees and other beneficial insects. Follow the label for timing and any pre-harvest interval, and wash produce well before eating, paying attention to the inner folds of heads where caterpillars and frass hide. For light pressure, hand-picking alone may be all you need.
How do I get cabbageworms out of a cabbage or broccoli head?
Prevention beats extraction, so a row cover from transplant is the real answer. If caterpillars are already inside a head, soak the cut head in cold salted or vinegared water for several minutes, which makes hidden caterpillars float out, then rinse well. Inspect the inner folds where they hide along with their dark frass before cooking.
The bottom line
The imported cabbageworm is the velvety green larva of the white butterfly, but it responds to the same plan as the rest of the brassica caterpillar complex. Cover the bed from transplant, which you can do all season because brassicas need no pollination, then hand-pick stragglers and eggs and reach for BT only when pressure spikes. Focus on protecting heads and growing points, time your plantings with the calendar to dodge peak butterfly season, and clean up after harvest to keep next year lighter.
