What is this on my tomato plant?
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The picture shows a tomato hornworm with pupal cases of a parasite attached. The tomato hornworm is a caterpillar that is a serious pest of tomato, and will eat the foliage. Nature helps us out with this one, but means of a small wasp that is a parasite on the caterpillar. The braconid wasp lays its eggs on the caterpillar, the eggs hatch, the small wasp larvae feed on the insides of the caterpillar. As the wasps grow and develop, the caterpillar dies. By the time they are adults and ready to fly the caterpillar is done. So, although you may feel that it harms the caterpillar, it is nature's perfect biological control of this tomato pest. Of course not all caterpillars of the tomato hornworm get parasitized, so their populations are still around.