The insects eating your tomato plants
The most common tomato pests are hornworms, whiteflies, spider mites, aphids, and flea beetles. Hornworms are large green caterpillars that can strip a plant bare in days. Whiteflies cluster on leaf undersides and drain plant sap, turning leaves yellow. Spider mites create fine webbing and cause stippled, yellowing leaves. Aphids are small soft-bodied insects that gather on new growth and excrete a sticky residue. Flea beetles are tiny dark beetles that chew small round holes in leaves, especially on seedlings.
Each pest damages plants differently and appears at different times in the growing season. Knowing which insect you have determines what you can do about it. The damage pattern — holes, yellowing, webbing, or wilting — tells you which pest is present.
Key Takeaways
- Hornworms are large green caterpillars that eat entire leaves and can be found by looking for dark droppings on lower leaves.
- Whiteflies and spider mites cluster on the undersides of leaves and are easiest to spot by flipping a leaf over and looking closely.
- Aphids and flea beetles attack new growth first, so check the top of the plant and seedlings before checking older leaves.
- Most tomato insects can be managed by hand-picking, spraying with water, or using neem oil, without removing the plant.
Hornworms: large caterpillars that eat whole leaves
Tomato hornworms are the largest pest you will encounter. They are fat green caterpillars, usually 3 to 4 inches long, with white stripes running down their sides and a horn-like projection on the rear end. A single hornworm can eat an entire leaf in one sitting and will defoliate a plant rapidly.
Look for dark droppings on the soil or lower leaves — these are a sign hornworms are feeding above. Scan the plant during early morning or late afternoon when hornworms are most active. They blend in with the foliage, so look along the main stem and thick branches first. If you find one, pick it off by hand and drop it into soapy water. Hornworms appear mid-summer onward, usually one or two per plant.
If you see a hornworm covered in small white cocoons, leave it alone — parasitic wasps have laid eggs inside it, and those wasps will kill future hornworms. This is free pest control working in your favor.
Whiteflies: tiny insects that cluster on leaf undersides
Whiteflies are small white insects about the size of a grain of salt. They live on the undersides of leaves in large groups and suck plant sap, which weakens the plant and causes yellowing. When you brush a leaf, they fly up in a small cloud.
Check the undersides of leaves regularly, especially on new growth at the top of the plant. Early detection matters because whiteflies reproduce quickly in warm weather. Spray the undersides of affected leaves with a strong stream of water from the hose to knock them off. Repeat every three days for two weeks. If the infestation is heavy, spray with neem oil according to label directions, hitting the undersides thoroughly.
Whiteflies thrive in hot, dry conditions. Keeping the soil consistently moist and avoiding overhead watering in the heat of the day can slow their spread.
Spider mites: pests that create fine webbing
Spider mites are nearly invisible to the naked eye but leave obvious signs. Affected leaves develop a stippled, yellowed appearance, and fine webbing appears between leaves and stems. The plant looks dusty or dull rather than glossy green.
Spider mites prefer hot, dry conditions and spread rapidly in summer heat. Check the undersides of leaves with a magnifying glass if you suspect them — you may see tiny moving dots. Spray the plant thoroughly with water, hitting both sides of every leaf, every other day for a week. This removes mites and the webbing they hide in. If webbing returns, spray again. Neem oil also works but is less effective than water spray for spider mites.
Increasing humidity around the plant — by misting or grouping plants closer together — makes conditions less favorable for spider mites.
Aphids: soft-bodied insects on new growth
Aphids are tiny pear-shaped insects, usually green or black, that cluster on new leaves and stems. They suck sap and excrete a sticky substance called honeydew, which coats leaves and can turn black with sooty mold. Affected leaves curl, yellow, and may become distorted.
Check the top of the plant and the newest leaves first — aphids prefer tender growth. A strong spray of water from the hose removes most aphids and can be repeated every few days. Neem oil spray also works well and should be applied to all leaf surfaces, especially the undersides where aphids hide. Spray in early morning or late evening to avoid harming beneficial insects.
Ladybugs and parasitic wasps eat aphids naturally. Planting flowers like alyssum or yarrow nearby attracts these beneficial insects and reduces the need for spraying.
Flea beetles: tiny beetles that chew small round holes
Flea beetles are small dark beetles, usually black or striped, that chew small round holes in leaves. They jump when disturbed, which is how they got their name. Flea beetles are most damaging to seedlings and young transplants, where they can kill the plant if the infestation is heavy.
Look for the characteristic small round holes, especially on the top surfaces of leaves. On seedlings, check daily because damage can escalate quickly. Spray with neem oil or insecticidal soap according to label directions. Repeat every 7 to 10 days as needed. Row covers — lightweight fabric laid over plants — prevent flea beetles from reaching seedlings entirely, but must be removed once the plant flowers to allow pollination.
Flea beetles are most active in spring and early summer. Once plants are established and growing vigorously, they can tolerate flea beetle damage without serious harm.
When to spray and what to use
Hand-picking works for large pests like hornworms and is the first step for any infestation. For smaller insects, water spray removes many pests and costs nothing. Spray in early morning or late evening to avoid leaf burn and to protect beneficial insects that are active during the day.
Neem oil is a plant-based pesticide that disrupts the feeding and reproduction of most soft-bodied insects. It works best on whiteflies, aphids, and spider mites. Follow label directions carefully — neem oil can damage plants if applied in direct sun or extreme heat. Insecticidal soap is another low-toxicity option for aphids and whiteflies. Neither neem oil nor insecticidal soap harms hornworms, which require hand-picking or a product containing Bacillus thuringiensis (Bt), a naturally occurring bacterium.
Repeat any spray treatment every 7 to 10 days until the pest is gone. One process rarely solves the problem because eggs hatch over time.
Frequently Asked Questions
How do I know if an insect is actually eating my tomato plant?
Look at the damage pattern. Holes in leaves with clean edges usually mean beetles or caterpillars. Yellowing leaves with stippling (tiny dots) usually mean spider mites or whiteflies. Curled or distorted new growth usually means aphids. Flip leaves over — if you see clusters of tiny insects, you have whiteflies or aphids. If you see fine webbing, you have spider mites.
Can I use the same spray for all tomato insects?
No. Neem oil and insecticidal soap work on soft-bodied insects like aphids and whiteflies but not on hornworms or beetles. Water spray works on whiteflies and spider mites but not on aphids or beetles. Hand-picking is the only method that works on hornworms. Check the label of any product to see which pests it targets.
Will insects kill my tomato plant?
Most insects cause damage but do not kill established plants. Hornworms and heavy whitefly infestations can defoliate a plant, which slows fruit production. Flea beetles can kill seedlings. Spider mites and aphids weaken plants but rarely kill them outright. Early detection and treatment prevent serious damage.
What time of year do tomato insects appear?
Flea beetles attack seedlings in spring. Aphids and whiteflies appear once weather warms, usually late spring through summer. Hornworms emerge mid-summer onward. Spider mites thrive in hot, dry conditions and are worst in late summer. Monitoring throughout the growing season catches infestations early.