07/28/2026
It is officially tomato hornworm caterpillar (Manduca quinquemaculata) season at the Nature Center. We found 10 tomato hornworms that were parasitized by the Cotesia wasp (Cotesia congregate) which is the natural enemy of tomato hornworms. We were lucky enough to snap a picture of a newly emerged wasp, which is a rare sight, as many people have never seen the tiny parasitoid that quietly and efficiently lays their eggs inside of the tomato hornworms. Usually, the only time we know that the Cotesia wasps were present is after finding caterpillars with white cocoons coming out of their backs.
If you see any tomato hornworm caterpillars with white, rice sized cocoons protruding out of their backs, leave the caterpillars alone. The caterpillars cannot cause damage to your tomatoes once parasitized. It is easy to determine when the wasps emerge from the cocoons, as the tops of the cocoons will be open. Once the wasps emerge, the caterpillar will die within a few days.
If you want to encourage more Cotesia wasps to your vegetable garden, you should include small flowered, long blooming, nectar-producing plants near your vegetable garden like sweet alyssum, fennel, dill, and wild carrot. Plants like these will benefit the Cotesia wasps by providing them with the food and shelter needed to fuel their caterpillar parasitizing!
