Key takeaways
- Cabbage moth caterpillars are smooth and green to brown, not hairy and spotted like large whites
- They feed mostly at night and tunnel into hearts, leaving droppings inside
- Caterpillars are about from June to October, with two broods in most areas
- Fine insect mesh from planting day keeps egg-laying moths off
- Squash egg batches and pick caterpillars by torchlight before they reach the heart
- Clear old brassica stumps in autumn, as the pupae overwinter in the soil
Cabbage moth caterpillars are the ones you find tunnelling into the heart of a cabbage, often after dark. They come from a night-flying, grey-brown moth, the cabbage moth (Mamestra brassicae). That makes them easy to miss until the damage is done.
The good news is that fine insect mesh and a few regular checks keep them in check. This guide shows you how to recognise the moth and its caterpillars and how to protect your crops. For the white butterflies and their caterpillars, see the cabbage white butterfly guide.
How to identify the cabbage moth
The adult moth is stocky, with mottled grey-brown wings about 4cm across. Look for a pale kidney-shaped mark on each forewing. It flies at night from late spring to early autumn, so you’ll rarely see it.
The caterpillars are what you’ll notice. They are smooth, not hairy, and grow to about 4cm long. Young ones are green. Older ones are usually darker, from green to brown or almost black, with a pale stripe along each side.
Eggs are laid in batches on the undersides of leaves. They’re small, pale and ribbed, and darken just before they hatch.
Smooth and plain, with no hairs or bright spots. Cabbage moth caterpillars blend in well, which is why they’re so easy to miss.
Cabbage moth or cabbage white?
Several caterpillars eat brassicas, so it helps to know which you’ve got. The controls overlap, but the timing and habits differ.
| Feature | Cabbage moth | Large white | Small white |
|---|---|---|---|
| Adult | Grey-brown moth, flies at night | White butterfly, flies by day | White butterfly, flies by day |
| Caterpillar | Smooth, green to brown or blackish | Hairy, yellow with black spots | Velvety, plain green |
| Eggs | Batches under leaves | Yellow clusters | Single eggs, often near the leaf vein |
| Feeding | Alone, mostly at night, into the heart | In groups, on outer leaves | Alone, often into the heart |
Tiny pale green caterpillars that wriggle wildly when touched are likely diamondback moth. The diamondback moth guide covers that pest.
What cabbage moth damage looks like
Young caterpillars graze the leaf surface, leaving thin, see-through windows. As they grow, they chew ragged holes right through the leaves.
The real trouble starts when they tunnel into the heart. They feed inside cabbages, Brussels sprouts and cauliflower curds, leaving dark droppings behind. A head can look fine from outside and be spoiled once you cut it open.
All the cabbage-family crops are at risk: cabbage, cauliflower, broccoli, Brussels sprouts, kale, kohlrabi and oriental greens. The caterpillars will also eat some other plants, such as lettuce, when they’re hungry.
Droppings in the heart are the giveaway. By the time you see this, the caterpillars are well inside, so earlier checks pay off.
When cabbage moths are active
In most of the UK there are two broods a year. Moths fly from late May, and the first caterpillars appear in June and July. A second brood follows from August into October. Further north there may only be one.
The caterpillars pupate in the soil when fully grown. The last brood stays there over winter and hatches the following spring. That’s why old brassica beds can produce moths even under fresh mesh. Moving brassicas to a new bed each year, as in a four-year crop rotation, helps avoid this.
How to protect brassicas from cabbage moth
Fine insect mesh is your best defence. Combine it with regular checks and autumn clearing and you’ll keep most damage away.
Cabbage moth caterpillars feed after dark. A quick torchlight check finds the ones hiding in the heart by day.
1. Cover crops with fine mesh. Put it on at planting time. Wide butterfly netting keeps out butterflies but may not stop moths, so choose fine insect mesh. It also keeps out cabbage root fly and flea beetle. Hold it above the plants on hoops, so it doesn’t touch the leaves, and weigh down the edges.
2. Check leaves weekly. Turn leaves over and squash any egg batches. Pick off young caterpillars while they’re still on the outer leaves.
3. Go out after dark. Older caterpillars feed at night. A torchlight check finds far more than a daytime look. Pick them off and squash them, or put them out for the birds.
4. Welcome predators. Birds, ground beetles and tiny parasitic wasps all eat eggs or caterpillars. A log pile, a strip of flowers such as yarrow and calendula, and a bug hotel nearby all help.
5. Clear up in autumn. Pull up old stumps after harvest and lightly fork the soil. This brings pupae up for birds to find.
Fine mesh on hoops keeps moths off from day one. Keep it clear of the leaves and weigh down the edges.
Warning: If a heavy attack does call for a spray, use an approved insecticide labelled for caterpillars on brassicas and follow the label exactly. Never spray plants in flower. Home-made sprays aren’t approved for garden use.
Do pheromone traps help?
A pheromone trap is a monitoring tool, not a cure. It attracts male moths, so a catch tells you the moths are flying.
Hang one near your brassicas from May. When you start catching moths, step up your egg checks a week or two later. The trap won’t stop females laying eggs, so keep the mesh on.
Moths on the sticky card mean egg-laying is under way. Use it as your cue to start checking leaves more often.
Common mistakes with cabbage moth
Using wide butterfly netting. It may let moths through. Use fine insect mesh.
Only checking in daylight. The bigger caterpillars hide in the heart by day. Go out with a torch.
Waiting for damage in the heart. By then, the caterpillars are hard to reach. Look for eggs and young caterpillars on the outer leaves.
Leaving mesh touching the leaves. Moths can lay eggs through mesh that rests on the plant. Use hoops.
Skipping the autumn clear-up. Pupae overwinter under old brassicas. Clear stumps and fork the soil lightly.
Cabbage moth calendar
| Month | What to do |
|---|---|
| March to April | Clear any old stumps. Rotate brassicas to a new bed. Check mesh for holes |
| May | Plant out under fine mesh. Hang a pheromone trap |
| June to July | Weekly egg checks under leaves. Torchlight checks for caterpillars |
| August to September | Second brood. Keep checking leaves and hearts |
| October | Final checks. Harvest and use remaining heads |
| November | Pull up old stumps and lightly fork the soil |
| December to February | Plan next year’s beds and mend mesh |
Frequently asked questions
Is the cabbage moth the same as the cabbage white butterfly?
No, they are different insects. The cabbage moth is a grey-brown moth that flies at night. Cabbage whites are white butterflies that fly by day. Their caterpillars look different too. Cabbage moth caterpillars are smooth and plain, while large white caterpillars are hairy and yellow with black spots.
When should I start checking my brassicas for cabbage moth?
Start in late May and keep checking weekly until October. Look under the leaves for batches of small, pale eggs and for young caterpillars grazing. Older caterpillars hide in the heart by day, so a torchlight check after dark finds more.
What does cabbage moth damage look like?
Ragged holes in the leaves and droppings deep inside the heart. Young caterpillars graze the leaf surface, leaving thin see-through patches. Older ones tunnel into cabbage hearts and cauliflower curds, so a plant can look fine outside but be spoiled inside.
What netting keeps cabbage moths out?
Fine insect mesh, not wide butterfly netting. Fine mesh keeps out moths, butterflies, cabbage root fly and flea beetle. Put it on at planting time, hold it above the leaves on hoops and weigh down the edges so nothing can crawl under.
Will birds and other predators control cabbage moth?
They help but rarely solve it alone. Birds pick off caterpillars, and ground beetles and parasitic wasps take eggs and young caterpillars. Use them alongside mesh and regular checks.
How does cabbage moth survive the winter?
As pupae in the soil under and around last year’s brassicas. They hatch into moths in late spring. Clearing old stumps in autumn and lightly forking the bed exposes them to birds and frost.
Do pheromone traps stop cabbage moth damage?
No, they only tell you when the moths are flying. Traps catch some male moths, but females still lay eggs. Use a trap as a reminder to step up egg checks a week or two after the first catches.
Want strong plants that shrug off damage? Read the guide to growing cabbage for sowing, spacing and mesh timings, or browse more pest control guides.
Our team produces practical UK gardening guidance from source research, contributor records and established horticultural practice. Editorial standards are overseen by Matt W.
