Why Are There Holes and Worms Inside My Tomatoes?

Few things turn the stomach like cutting into a ripe tomato and finding a tunnel, some dark crumbly waste, and a caterpillar curled up inside. A worm in the fruit means a caterpillar bored its way in to feed, and once inside, it ruins the tomato and opens it to rot. The main offenders are well known, and with the right timing you can protect the fruit before they ever get in. Let me explain who is doing it and how to stop them.

The tomato fruitworm

The most common culprit is the tomato fruitworm, the same caterpillar known as the corn earworm. The adult is a night-flying moth that lays single eggs on the leaves near the fruit. When the eggs hatch, the young caterpillars head straight for the tomatoes and bore in, usually near the stem end. They tunnel through the flesh as they feed, leaving a hole and a mess of dark droppings inside, and they often move from fruit to fruit, damaging several. A single entry hole is the classic sign, and the fruit usually rots from the inside out soon after.

Hornworms and other borers

The large tomato hornworm, better known for stripping foliage, will also chew into fruit, leaving bigger, rougher gouges rather than a neat bore hole. Various other caterpillars and the occasional beetle grub can get into fruit too, especially where the skin is already damaged — a crack, a catfaced scar or an old insect wound is an open invitation. So good fruit hygiene, picking off cracked or damaged tomatoes promptly, removes the easy entry points borers rely on.

The key is stopping them before they enter

Here is the crucial point: once a caterpillar is inside the fruit, no spray can reach it. All effective control happens before they bore in, while the young caterpillars are still on the surface. That is why timing and scouting matter so much. Inspect your plants regularly for the small caterpillars and for the eggs on leaves near developing fruit, and remove any you find. Hand-picking is genuinely effective in a home garden.

Using Bt and biological control

The most reliable treatment is Bt, a naturally occurring bacterium that specifically targets caterpillars and is harmless to people, pets and beneficial insects. Sprayed onto the foliage and fruit surface, it is eaten by the young caterpillars as they feed before boring in, and it kills them. Apply it when you first notice the caterpillars or moth activity, and reapply as directed, especially after rain. Encouraging natural predators and parasitic wasps, which attack the eggs and young larvae, adds another layer of defence.

Deal with affected fruit

Any tomato you find with a worm or bore hole should be picked and removed promptly — do not leave it on the plant or drop it on the ground, because the caterpillar will simply move on or pupate and continue the cycle. Bin damaged fruit, keep up your scouting, and clear away debris at the end of the season to reduce the overwintering population. Catch them early, lean on Bt, and you will be slicing into clean, sound tomatoes instead of unwelcome surprises.