If you’ve spotted black caterpillars on tomato plants, you’re likely dealing with a common but destructive garden pest. These hungry larvae can quickly strip your prized tomatoes of their leaves and fruit. Don’t worry, though. Identifying and controlling them is straightforward with the right approach.
This guide will help you figure out exactly which caterpillar you’re facing and give you clear, effective methods to protect your garden. We’ll cover everything from organic sprays to simple hand-picking.
Black Caterpillars on Tomato Plants
Not all black caterpillars are the same. The most common culprits on tomatoes are the tobacco hornworm and the tomato hornworm. While they are often green, they can appear darker or have black markings. True black caterpillars might be cutworms, armyworms, or even the larvae of the swallowtail butterfly (which don’t harm tomatoes). Correct identification is your first step to effective control.
Common Black or Dark Caterpillars on Tomatoes
- Tobacco Hornworm (Manduca sexta): Has seven diagonal white lines and a red “horn.” It’s usually green but can look blackish.
- Tomato Hornworm (Manduca quinquemaculata): Features eight V-shaped markings and a black horn. Again, often green.
- Black Cutworm (Agrotis ipsilon): A smooth, greasy-looking gray-to-black caterpillar that chews through stems at soil level.
- Beet Armyworm (Spodoptera exigua): Small, hairy, and can range from green to black. They feed in groups.
Why Are They in My Garden?
These caterpillars are simply the larval stage of moths and butterflies. The adults lay eggs on the undersides of tomato leaves. When the eggs hatch, the caterpillars start eating to grow. They’re attracted to healthy, leafy plants, so your thriving tomato patch is a perfect target.
The Damage They Cause
Caterpillar damage is usually easy to spot. You’ll see large, irregular holes eaten in leaves. Sometimes, they eat the entire leaf, leaving only the stems. Hornworms can also chew holes in the green tomatoes themselves. Cutworms will sever young seedlings overnight. If you see dark green or black droppings (frass) on leaves, look directly above—you’ll likely find the culprit.
Organic and Natural Control Methods
Starting with the least toxic options is best for your garden’s ecosystem. These methods are safe for you, beneficial insects, and the environment when used correctly.
Hand-Picking
This is the most immediate and effective method for larger caterpillars like hornworms. Go out in the early morning or evening when they are most active. Wear gloves if you prefer. Drop them into a bucket of soapy water. A flashlight at night can make them easier to spot, as they glow under UV light!
Beneficial Insects and Birds
Encourage nature’s helpers. Birds love caterpillars. Install a bird feeder or bath nearby. You can also introduce or attract beneficial insects.
- Parasitic Wasps: Tiny wasps lay eggs on hornworms. If you see a hornworm with white rice-like cocoons on its back, leave it! Those are new wasps that will kill that caterpillar and go on to help many more.
- Ladybugs & Lacewings: Their larvae eat caterpillar eggs and small larvae.
Organic Sprays and Treatments
When hand-picking isn’t enough, these sprays can help.
- Bacillus thuringiensis (Bt): This is a natural soil bacteria that is toxic to caterpillars when they ingest it. It’s harmless to humans, pets, and beneficial insects. Spray it thoroughly on leaves, especially the undersides.
- Spinosad: Another organic insecticide derived from soil bacteria. It’s effective against a broad range of caterpillars but can harm bees if sprayed directly on them. Apply it in the late evening when bees are not active.
- Neem Oil: This plant-based oil disrupts the feeding and growth cycles of insects. It needs to be reapplied regularly, especially after rain.
Prevention is Key
Stopping an infestation before it starts saves you alot of work later. A few simple habits can make a big difference.
Garden Sanitation
Keep your garden tidy. Remove plant debris at the end of the season, as pupae can overwinter in the soil. Till the soil in fall or early spring to expose and destroy overwintering pests.
Crop Rotation and Companion Planting
Don’t plant tomatoes in the same spot every year. Rotate them with unrelated crops like beans or corn. Companion planting can also deter pests. Strong-smelling herbs like basil, dill, and marigolds are said to repel the moths that lay caterpillar eggs.
Physical Barriers
For cutworms, use collars. Make rings from cardboard, paper cups, or toilet paper tubes and place them around the base of young seedlings, pushing them an inch into the soil. Floating row covers over young plants can prevent moths from laying eggs in the first place, but remember to remove them when plants flower to allow for pollination.
When to Consider Chemical Controls
In severe infestations where organic methods haven’t sufficed, you might consider synthetic insecticides. Use these as a last resort, as they can harm beneficial insects and the wider environment. Always read and follow the label instructions precisely. Look for products containing carbaryl or permethrin, which are labeled for caterpillar control on vegetables. Apply only to affected plants and only when absolutely necessary.
Frequently Asked Questions (FAQ)
What are the black worms eating my tomato plants?
They are likely caterpillar larvae of moths. The most common are hornworms (which can appear dark), cutworms, or armyworms. Check their specific markings to identify them correctly.
Are black caterpillars on tomatoes poisonous?
Most common tomato caterpillars are not poisonous to humans. However, some, like the hornworm, can have a mild toxin from the plants they eat that may irritate sensitive skin, so wearing gloves during hand-picking is a good idea.
How do I get rid of caterpillars on my tomato plants naturally?
Start with hand-picking. Then, encourage birds and beneficial insects. If needed, apply organic treatments like Bt or neem oil. Physical barriers like cutworm collars can also be very effective for specific pests.
Will dish soap kill caterpillars on plants?
A mild soapy water spray can suffocate and kill small, soft-bodied caterpillars on contact. Mix 1-2 tablespoons of plain dish soap per gallon of water and spray directly. It’s not always effective on larger caterpillars and may need repeat applications. Rinse plants after a few hours to prevent leaf damage.
Dealing with black caterpillars on tomato plants is a manageable part of gardening. By staying observant, acting quickly with the gentlest method first, and focusing on prevention, you can keep your tomato plants healthy and productive all season long. Your reward will be a bountiful harvest of homegrown tomatoes, earned through your careful stewardship of the garden.