If you're growing tomatoes, keep an eye out for hornworm caterpillars. These hungry pests can grow up to four inches long and will defoliate your tomatoes in just a few days.
Both tomato hornworms and tobacco hornworms have light green bodies with diagonal white markings along their sides, and a small horn at the back of their bodies.
It's easy to overlook young caterpillars, since they're small and blend in well. It's easier to spot signs of damage like bare stems or caterpillar droppings.
Look carefully for these pests, and be sure to check the undersides of leaves. Use the "pick and squash" method to get rid of any that you find, or use a biorational insecticide like Bt.