Black Onion Fly

Tritoxa flexa · Order: Diptera · Family: Ulidiidae

No source yet on danger. We have no source yet on whether it bites, stings or damages anything.
Black Onion Fly
Photo: Alie / C.A. Kratzer, CC BY-SA

The black onion fly, Tritoxa flexa, is a picture-winged fly in the family Ulidiidae. It occurs in Canada and the United States.

Source: Wikipedia

Where it comes from

It is native to Canada and the United States.

Source: Wikipedia

Where it is found in the US

Recorded in 30 of 51 states and DC. Most records: Ohio, Pennsylvania, Virginia, Maryland, Kentucky, Illinois, North Carolina, Indiana.

Darker = more records. Counts are museum and citizen-science records, not population size.

Source: GBIF

Status: native in North America; native in Canada. Source: iNaturalist

Months it is reported in the US

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Source: GBIF

More photos

Black Onion Fly photo 3
Photo: jrcagle, CC BY
Black Onion Fly photo 4
Photo: Healthy Yards, CC BY
Black Onion Fly photo 5
Photo: Chris, CC BY-SA
Black Onion Fly photo 6
Photo: Amy Schnebelin, CC BY

Same family (Ulidiidae)

Common Picture-winged FlyCommon Picture-winged FlyDelphinia pictaPeacock FlyPeacock FlyCallopistromyia annulipesPicture-winged FlyPicture-winged FlyPhysiphora alceaeEuxesta elutaEuxesta elutaEuxesta elutaDamages trees, gardens or cropsPterotaenia fasciataPterotaenia fasciataPterotaenia fasciata

Sources

  • Wikipedia: https://en.wikipedia.org/wiki/Tritoxa_flexa

Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia

Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-22.

How this page works

This is one bug's fact sheet. The colored box at the top says whether it is dangerous. Sections below cover how to recognize it, whether it is a pest, and how to deal with it. The US map shows which states have records; tap a state to see other bugs there.

Every fact on Bug FAQ comes from a named source (university extension sites, government agencies, GBIF, iNaturalist, Wikipedia). The source is linked next to each section. If we have no source for something, we leave it out.