House Fly vs Blow Fly
House Flies and blow flies are easy to mix up at a glance, but a few details separate them quickly. Here is how to tell which one you found and what, if anything, you should do about it.
Quick answer
Check for this first. A house fly has four dark lengthwise stripes on a gray thorax, while a blow fly has metallic green, blue or bronze body.
Side-by-side comparison
| House Fly | Blow Fly | |
|---|---|---|
| Group | Flies & Mosquitoes | Flies & Mosquitoes |
| Scientific name | Musca domestica | Lucilia sericata |
| Size | 6–7 mm | 8–12 mm |
| Colors | Gray and Black | Green, Blue and Metallic |
| Legs | 6 legs | 6 legs |
| Wings | Yes | Yes |
| Bites or stings | No | No |
| Risk | Nuisance | Nuisance |
| Key feature | Four dark lengthwise stripes on a gray thorax | Metallic green, blue or bronze body |
Key differences
- Size: Blow Flies are larger, reaching 12 mm, while house flies top out around 7 mm.
- Color: House Flies are gray and black; blow flies are green, blue and metallic.
- Signature feature: House Flies: four dark lengthwise stripes on a gray thorax. Blow Flies: metallic green, blue or bronze body.
How to identify house flies
The most common fly in homes, a dull gray fly with four dark stripes on its thorax. It breeds in garbage, manure and rotting food and lands on nearly everything.
- Four dark lengthwise stripes on a gray thorax
- Red compound eyes
- Sponging mouthparts that cannot bite
How to identify blow flies
A shiny, metallic green or blue fly that lays eggs on dead animals, meat and garbage. A sudden swarm indoors often signals a dead mouse or bird in a wall or attic.
- Metallic green, blue or bronze body
- Larger and louder than a house fly
- Often appears suddenly in large numbers indoors
Which one is more dangerous?
Neither is more dangerous than the other; both are rated nuisance on our scale.
House flies don't bite, but they can carry bacteria that cause food poisoning. Blow flies don't bite but can carry bacteria from rotting material.
Where and when you'll see each
House Flies turn up in the kitchen and indoors, mostly in spring, summer and fall. Blow Flies turn up in the kitchen and indoors, mostly in spring, summer and fall.
Because they share habitat, you may find both in the same place, so check each individual.
What to do if you find one
House Flies: Keep trash tightly covered and take it out often. Read the full removal guide for more.
Blow Flies: Search for and remove any dead animal, then clean the area. Read the full removal guide for more.
Biology: flies & mosquitoes
Flies have only one pair of working wings; the second pair is reduced to small balancing knobs called halteres. They go through complete metamorphosis, and the larvae, called maggots, need moist organic material such as garbage, soil, drain film or standing water.
Frequently asked questions
What is the main difference between house flies and blow flies?
Size: Blow Flies are larger, reaching 12 mm, while house flies top out around 7 mm.
Which is bigger, a house fly or a blow fly?
House Fly: 6–7 mm. Blow Fly: 8–12 mm.
Do house flies or blow flies bite?
House Flies do not bite. Blow Flies do not bite.
Where are they usually found?
House Flies: in the kitchen and indoors. Blow Flies: in the kitchen and indoors.