Pest profile

Braconid Wasps

Braconidae (shown: Cotesia congregata) · Hymenoptera: Braconidae[5]

The white, rice-like cocoons on a tomato hornworm belong to a small braconid wasp. Braconids are parasitic wasps whose larvae grow inside caterpillars and other insects and kill them.[1][3]

Hornworm caterpillar covered in dozens of white, rice-like braconid wasp cocoons on a plant stem
Hornworm caterpillar covered in dozens of white, rice-like braconid wasp cocoons on a plant stem. (c) Eridan Xharahi, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Cotesia adults are small, dark wasps that resemble flying ants or tiny flies, with antennae curved upward rather than elbowed.[2]
  • The female's abdomen narrows to a downward-curving ovipositor used to lay eggs.[2]
  • Cocoons are small silken cases, white to yellowish, attached to the host caterpillar or nearby leaves.[1][2][3]
  • On a tomato hornworm the cocoons stick out of the body like grains of white rice.[1]

Where it lives

More than 1,000 braconid species occur in the United States, attacking the larvae of beetles, caterpillars, flies and sawflies.[3]

US map: public records from 38 states since 1990 (GBIF).

Biology and life cycle

A female lays eggs inside a young caterpillar; Cotesia glomerata places about 20 to 60 in each imported cabbageworm.[2]

The wasp larvae feed inside the living host, then emerge to spin cocoons on or near it, and the host dies.[1][2]

Egg to adult takes about 22 to 30 days for C. glomerata, and about two weeks in summer for the alfalfa caterpillar Cotesia.[2][3]

Adults feed on honeydew and nectar and live 2 to 3 weeks.[3]

Damage and signs

  • They don't feed on plants. By midseason about half of imported cabbageworm larvae may be parasitized by C. glomerata, rising to 60 to 75 percent late in the season.[2]

Health risk

Parasitoid wasps such as braconids do not sting people.[4]

Control

Prevention

If a hornworm carries white cocoons, leave it in the garden so the adult wasps can emerge and parasitize more hornworms.[1]

Biological control

Parasitoid wasps are very sensitive to insecticides, so avoid or limit chemical sprays.[4][1]

Flowering plants supply nectar that nourishes adult parasitic wasps.[3]

Common questions

What are the white things sticking out of my hornworm?
They're cocoons of a braconid wasp. Its larvae fed inside the hornworm, which will die when the adult wasps emerge.[1]
Will these wasps sting me?
No. Parasitoid wasps are not interested in people and do not sting them.[4]
Can I buy them?
Not this one: Cotesia glomerata isn't commercially available, so gardens rely on wild populations.[2]

Sources

  1. University of Minnesota Extension, “Tomato hornworms.” extension.umn.edu/yard-and-garden-insects/tomato-hornworms (accessed 2026-10-06)
  2. Cornell University College of Agriculture and Life Sciences, “Biological Control: A Guide to Natural Enemies in North America: Cotesia glomerata.” biocontrol.entomology.cornell.edu/parasitoids/cotesia.php (accessed 2026-10-06)
  3. University of California Statewide IPM Program, “Alfalfa Caterpillar Cotesia Parasitoid (Natural Enemies Gallery).” ipm.ucanr.edu/natural-enemies/alfalfa-caterpillar-cotesia-parasitoid/ (accessed 2026-10-06)
  4. University of Maryland Extension, “Parasitoid wasps.” extension.umd.edu/resource/parasitoid-wasps (accessed 2026-10-06)
  5. iNaturalist, “Cotesia congregata taxon page (order and family).” www.inaturalist.org/taxa/1449989 (accessed 2026-10-06)

Updated 2026-10-13. Built from sourced records. Spot an error? Tell us.