Stable fly vs Horn fly
These two are easy to mix up. Here's how to tell a stable fly from a horn fly, and whether either one bites or stings.
Stable fly
Stomoxys calcitrans
Horn fly
Haematobia irritans
≠The key differences
Horn flies are smaller, stay on cattle most of the time and rarely disperse; stable flies are larger, more likely to bite off-host animals and are stronger fliers.
Stable flies are larger (about house-fly size), have a checkerboard-patterned abdomen, rest on legs, fences and walls, and readily bite humans; horn flies are about half that size and remain on the backs and sides of cattle.
⚖︎Side by side
| Stable fly | Horn fly | |
|---|---|---|
| To humans | Painful bite | Blood feeder |
| Size | 5-7 mm long | 3-5 mm body length (about half the size of a house fly) |
| Colours | Gray, Dark brown, Black | Gray, Black, Dark brown |
| Family | Muscidae | Muscidae |
| Habitat | Farmyards, livestock bedding, decaying vegetation, damp compost, roadside vegetation and areas with mixed manure and organic matter | On cattle and other bovids, in pastures and areas with fresh dung where larvae develop |
| Range | Cosmopolitan: found worldwide in temperate, subtropical and tropical regions where livestock and suitable breeding material occur | Originally Eurasian, now widespread in North America, South America, Africa and other regions where cattle are raised |
| Active | Warm months (spring to autumn in temperate regions), active in daylight especially mid-morning to late afternoon | Active in warm months; most abundant spring through fall in temperate zones and year-round in some warmer regions; day-active |
| Pest? | Yes | Yes |
🔍How to spot a stable fly
- Look for a 5-7 mm grayish fly with darker longitudinal thoracic markings and patterned abdomen.
- Check for a rigid, forward-pointing proboscis beneath the head used for piercing skin (visible in close photos) — unlike non-biting house flies.
- Observe behavior: stable flies actively bite and commonly rest on legs and lower body of livestock and humans, often repeatedly.
- Compare with house fly: stable flies are more robust, have piercing mouthparts and bite; house flies have sponge-like mouthparts and do not bite.
🔍How to spot a horn fly
- Very small fly 3-5 mm long that stays on cattle, often in large numbers on the back, shoulders and flanks, typically resting head-down.
- Darker gray to black body with faint thoracic stripes and a narrow, pointed profile compared with house flies.
- Persistent on the host and flies only short distances; frequently moves across the animal to feed.
- Piercing-sucking mouthparts visible on close inspection; adults cluster on legs, belly and sides of cattle.
?Frequently asked questions
What is the difference between a stable fly and a horn fly?
Horn flies are smaller, stay on cattle most of the time and rarely disperse; stable flies are larger, more likely to bite off-host animals and are stronger fliers. Stable flies are larger (about house-fly size), have a checkerboard-patterned abdomen, rest on legs, fences and walls, and readily bite humans; horn flies are about half that size and remain on the backs and sides of cattle.
Is a stable fly or a horn fly more dangerous?
Stable fly: Painful bite. Horn fly: Blood feeder. Stable flies deliver painful, biting wounds while feeding on blood. Horn flies are primarily a livestock pest and only occasionally bite people who work closely with infested cattle; bites are brief and itchy or mildly painful.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.