Pest profile

Swede Midge

Contarinia nasturtii · Diptera: Cecidomyiidae[2]

You'll rarely see swede midges, but their larvae can keep broccoli from heading and leave twisted, scarred brassica plants.[1]

Distorted, crumpled growing tip of a young cabbage-family plant held between fingers, typical of swede midge damage
Distorted, crumpled growing tip of a young cabbage-family plant held between fingers, typical of swede midge damage. (c) Juan C. Espinosa, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are tiny delicate flies about 2 mm long, light brown to light orange.[1]
  • Larvae are 1 to 4 mm, creamy white when young and lemon yellow when mature, hidden in the growing point.[1]
  • The key sign is brown, corky scarring near the growing point, with distorted leaves and multiple or missing heads.[1]

Where it lives

An invasive fly, it was first found in Minnesota in 2016 in parts of Hennepin and Ramsey counties and is established in Manitoba.[1]

Biology and life cycle

It overwinters in the top few centimeters of soil where brassicas grew and can stay dormant for several seasons.[1]

Adults live one to five days; larvae feed 7 to 15 days, then drop to the soil; there can be two to five generations a year.[1]

Damage and signs

  • Feeding distorts and scars leaves and stems and can prevent broccoli from forming a crown or cause multiple heads.[1]

Health risk

It attacks brassicas; Minnesota Extension mentions no risk to people.[1]

Control

Prevention

Don't start transplants in soil that may hold swede midge pupae.[1]

Where confirmed, don't plant brassicas in the same spot for one to three years.[1]

When to call a professional

Report suspected swede midge in Minnesota to the Minnesota Department of Agriculture.[1]

Common questions

Why did my broccoli never form a head?
Swede midge larvae feeding at the growing point can stop heading; look for corky brown scars.[1]
Can I see swede midges?
Unlikely; every stage is very small and larvae hide in the growing point.[1]

Sources

  1. University of Minnesota Extension, “Swede midge (Yard and garden insects).” extension.umn.edu/garden-and-home/yard-and-garden/yard-and-garden-insects/swede-midge (accessed 2026-10-06)
  2. iNaturalist, “Contarinia nasturtii taxon page (order and family).” www.inaturalist.org/taxa/202628 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.