Stable fly vs Face fly
These two are easy to mix up. Here's how to tell a stable fly from a face fly, and whether either one bites or stings.
Stable fly
Stomoxys calcitrans
Face fly
Musca autumnalis
≠The key differences
Stable flies look similar in size but have a proboscis for piercing and blood-feeding; they bite animals and humans and are generally more painful than non-biting face flies.
⚖︎Side by side
| Stable fly | Face fly | |
|---|---|---|
| To humans | Painful bite | Mechanical vector |
| Size | 5-7 mm long | 6-8 mm long |
| Colours | Gray, Dark brown, Black | Gray, Black, Yellow (face), Reddish (eyes) |
| Family | Muscidae | Muscidae |
| Habitat | Farmyards, livestock bedding, decaying vegetation, damp compost, roadside vegetation and areas with mixed manure and organic matter | Farms, pastures, meadows, and any area with cattle dung or livestock; also around barns, farm buildings and sometimes houses near livestock. |
| Range | Cosmopolitan: found worldwide in temperate, subtropical and tropical regions where livestock and suitable breeding material occur | Native to Europe and Asia; introduced and established across much of North America and present in temperate regions worldwide. |
| Active | Warm months (spring to autumn in temperate regions), active in daylight especially mid-morning to late afternoon | Active spring through autumn in temperate regions, day-active (diurnal) with peak activity in warm daylight hours. |
| 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 face fly
- Size 6-8 mm, similar to house fly but with a paler or slightly yellowish face.
- Thorax grey with four distinct dark longitudinal stripes.
- Abdomen with alternating light and dark patterning; large red eyes.
- Frequently rests on the faces or around eyes and nostrils of cattle and other animals.
?Frequently asked questions
What is the difference between a stable fly and a face fly?
Stable flies look similar in size but have a proboscis for piercing and blood-feeding; they bite animals and humans and are generally more painful than non-biting face flies.
Is a stable fly or a face fly more dangerous?
Stable fly: Painful bite. Face fly: Mechanical vector. Stable flies deliver painful, biting wounds while feeding on blood. Face flies do not bite or inject venom.
Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.