Parasitoid Wasps

Invite parasitoid insects to your next garden party.

Parasitoids insects tend to be specialized in the insects they feed on. They may only attack one type of insect, such as caterpillars, or in some cases, one species. The adults will look for hosts to lay their eggs on or in. Once the egg hatches, it will feed on its host, eventually killing it.

Most parasitoid wasps are small and easily confused with gnats. These small wasps attack aphids, whiteflies, mealybugs, caterpillars, and insect eggs. 

Insects that have been parasitized often look different. Parasitized aphids will eventually turn brown or black and paper-like. In some caterpillars, such as hornworms, the larvae will spin white cocoons on the outside of its host, which are commonly confused for eggs.

Some species of flies are also parasitoids. Adult tachinid flies lay eggs on or in their host caterpillars and beetles. The larvae of these flies tunnel into their host to feed, eventually killing it.

Gardeners can take steps to encourage good insects. While many natural enemy insects can be purchased, making some changes to how you manage your landscape can make it much more attractive to these insects and help keep them around long term.

  • Provide flowers for beneficial insects to feed on. Many beneficial insects will feed on nectar and pollen. This is especially important if the adults aren’t predators. Plants with small flowers, such as sweet alyssum, dill, fennel, garlic chives, coriander, and Queen Anne’s Lace, are good choices. Other common garden plants, including blanket flower, coneflower, cosmos, and sunflowers, will be visited by beneficial insects, too.
  • Cut back on or cut out insecticides. Most insecticides kill beneficial insects as well as pests.
  • If you are going to use insecticides, use a selective pesticide that is toxic to specific insects and won’t directly harm beneficial insects. For example, Bacillus thuringiensis kurstaki (Btk) only affects caterpillars. When using pesticides, make sure to read and follow all label directions.