Are Black Soldier Flies a Disease Risk?

"Flies raised on rotting food waste" sounds like a public health problem. It is worth understanding exactly why it is not.

How Flies Actually Spread Disease

A housefly is a vector because of a specific behavioural loop. It feeds on waste, picks up microbes on its body and in its gut, then lands on and feeds on human food, depositing them. It also regurgitates to liquefy food, which makes the transfer worse.

Every step of that loop requires the adult fly to feed.

Why the Black Soldier Fly Breaks the Loop

The adult black soldier fly has no functional mouthparts and does not feed. It has nothing to gain from your kitchen and no equipment to exploit it. It does not land on food, does not regurgitate on it, and has no reason to be indoors at all.

They Actively Displace Houseflies

This is the part that surprises people. A substrate colonised by black soldier fly larvae becomes less attractive to houseflies. The larvae change the substrate as they work it, and the effect on housefly oviposition is well enough documented that BSFL are used deliberately in manure management for this reason.

Adding black soldier fly to a waste stream tends to reduce the total fly problem.

Sensible Handling Anyway

None of this means a bin is sterile. The substrate is decomposing organic matter and should be treated as such:

• Wash your hands after handling a bin or its contents
• Do not site a bin against a kitchen door
• Keep it covered — mostly for moisture and other pests, not for the flies

See also are black soldier flies harmful.