The fastest way to get rid of caterpillars depends on the scale of your problem. For a few caterpillars on a small garden, handpicking them off plants in the early morning or evening works immediately. For larger infestations, a biological spray called Bt (Bacillus thuringiensis) kills caterpillars within days while remaining safe for humans, pets, and most beneficial insects. Beyond those two go-to options, a combination of physical barriers, companion planting, and habitat for natural predators can keep caterpillar populations low all season.
Handpicking: The Simplest First Step
If you’re dealing with a manageable number of caterpillars, picking them off by hand is the most targeted approach. Check the undersides of leaves, where caterpillars feed and hide during the day. Early morning and late evening are the best times, since many species are more active and visible during cooler hours. Drop them into a bucket of soapy water to dispatch them quickly.
Start scouting as soon as you notice adult moths or butterflies around your plants. White butterflies hovering near cabbage, broccoli, or kale signal that eggs are being laid. The sooner you find caterpillars, the less damage they’ll do. Small caterpillars are also far easier to control than mature ones. Beet armyworms, for example, become extremely difficult to kill with any method once they grow past half an inch.
Bt Spray: The Most Effective Organic Treatment
Bacillus thuringiensis kurstaki, sold as Bt or Btk, is a naturally occurring soil bacterium and the gold standard for caterpillar control in home gardens. When a caterpillar eats leaves coated with Bt spores, the proteins act as a gut toxin. The caterpillar stops feeding and dies from infection and starvation, typically within a few days.
Bt targets only the larvae of moths and butterflies. The toxic proteins cannot be activated in mammals, so it poses no risk to humans, pets, or wildlife. It’s also safe for honeybees, with one exception: the “aizawa” strain of Bt can harm bees, so stick with products labeled as kurstaki (Btk) for caterpillar control. As a precaution, avoid spraying any plants that are actively flowering, and don’t let spray drift into puddles or water sources bees might visit.
Timing matters. Bt works only when caterpillars ingest it, so spray it directly on the foliage they’re eating. It breaks down in sunlight within a few days, meaning you’ll need to reapply after rain or every week or so during active infestations. Apply it when caterpillars are still small for the best results.
Spinosad and Neem Oil
Spinosad is another organic option derived from a soil bacterium. It works primarily through ingestion: after a caterpillar eats treated foliage, it stops feeding within hours, though it may stay on the plant for up to two days before dying. Spinosad is effective against caterpillars, leaf miners, thrips, and some beetles, and it’s available in spray and bait formulations labeled for vegetables, ornamentals, and lawns.
The main drawback is that spinosad is toxic to bees. Never apply it to plants in flower, and always spray late in the day when pollinators are less active to reduce the risk.
Neem oil takes a different approach. It acts as a contact insecticide, feeding deterrent, and repellent. Products containing the refined compound azadirachtin also interfere with molting, preventing immature caterpillars from developing properly. Neem is less of a quick knockdown and more of a long-term suppression tool, useful for slowing population growth rather than eliminating an active infestation overnight. Products labeled as “clarified hydrophobic extract of neem oil” contain very little of the growth-disrupting compound and work mainly through smothering and repellency.
Floating Row Covers Block Moths Entirely
If you want to prevent caterpillars rather than fight them, floating row covers are one of the most reliable methods. These lightweight sheets of spun-bonded polyester or polypropylene drape over your crops, letting in light, water, and air while physically blocking moths and butterflies from landing and laying eggs. They’re especially effective for brassicas like cabbage, broccoli, and cauliflower, where imported cabbageworms, cabbage loopers, and diamondback moths are persistent problems.
The key is to install covers at planting time, before any eggs are laid. Bury the edges completely in soil so no gaps remain. For low-growing crops, you can lay the fabric directly on the plants with enough slack for growth. Taller or more delicate plants benefit from PVC hoops bent into the soil to create a frame that keeps the material off the leaves. You’ll need to lift the covers periodically to weed, but the tradeoff is a nearly caterpillar-free growing season.
One important note: practice crop rotation when using row covers. If caterpillar pupae overwinter in the soil beneath last year’s crop, covering that same bed the next year can trap emerging adults inside with your plants.
Companion Plants That Repel Moths
Certain herbs produce strong scents that interfere with a moth’s ability to locate its preferred host plant. Research from Iowa State University found that thyme planted around brassicas was the most effective deterrent for cabbage worms and cabbage loopers, followed by nasturtium and onion. For tomato hornworms and armyworms, basil and thyme were the standout performers, with separate studies confirming that basil helped repel hornworms from tomato beds.
Companion planting won’t eliminate caterpillars on its own, but it reduces egg-laying pressure and works well alongside other methods. Interplanting herbs throughout your vegetable rows, rather than grouping them at the edges, maximizes the scent-masking effect.
Attracting Natural Predators
Your garden already has allies. Birds, spiders, predatory insects, and parasitic wasps all feed on caterpillars or their eggs. Trichogramma wasps, tiny enough to be nearly invisible at less than a millimeter long, seek out caterpillar eggs and parasitize them before they hatch. You can buy and release these wasps, but University of Minnesota Extension recommends making your space welcoming to them instead, since that also benefits other beneficial insects and native bees.
To build habitat for natural predators, keep a variety of flowering plants blooming throughout the season. Adult parasitic wasps feed on pollen and nectar, so consistent flower availability is critical. Tolerate a low level of pest presence on your plants, since beneficial insects need something to eat to stick around. Most importantly, limit broad-spectrum pesticide use. Even organic sprays like spinosad can kill the very insects that would otherwise keep caterpillar populations in check.
Dealing With Tent Caterpillars in Trees
Caterpillars in trees present a different challenge. Eastern tent caterpillars build silken nests in branch forks in spring, while fall webworms enclose branch tips in loose webs later in the season. Both can defoliate branches, but healthy trees usually recover.
Early detection is your best tool. Look for egg masses on twigs during winter and scrape them off before spring. Once webs appear, destroy small nests by pruning out the affected branch or twisting a stick into the web to pull it apart and expose the caterpillars to predators. For larger infestations, spray Bt on the foliage around the nests while caterpillars are still small. Bt is effective against both species.
Natural enemies including birds, small mammals, spiders, and parasitic wasps keep these populations in check most years. Naturally occurring viruses and fungi also kill large numbers of tent caterpillars and webworms when humidity and temperatures are favorable, which is why severe outbreaks tend to collapse on their own after a year or two.
Identifying Common Garden Caterpillars
Knowing what you’re dealing with helps you choose the right timing and approach:
- Imported cabbageworm: Velvety green with a thin yellow stripe down the back. Feeds near the center of brassica leaves, close to the veins. Look for it as soon as white butterflies appear in the garden.
- Cabbage looper: Light green with white stripes along the sides and back, tapering toward the head. Arches its back like an inchworm when it moves. Check lower leaf undersides first.
- Tomato hornworm: Large, bright green with white diagonal stripes and a horn on the rear. Easily spotted by the dark droppings it leaves on lower leaves.
- Beet armyworm: Light green to black with fine white wavy lines on the back and a dark spot near the second pair of legs. Must be targeted while small.
- Cross-striped cabbageworm: Bluish-gray with black cross-stripes and yellow side stripes. Eggs are laid in clusters of 20 to 30, so infestations are often concentrated on a few plants.
- Diamondback moth larva: Small, yellowish-green, spindle-shaped with a forked tail. Creates small irregular holes in leaves. Check bud leaves on young transplants.
For all of these species, the principle is the same: scout early, act while caterpillars are small, and combine multiple methods for the most durable control.