Adult stable flies are between 5–7 mm in size and largely resemble the house fly, even having a four-striped thorax. However, they are light grey in colour; they have a broader abdomen that displays several dark spots in a “checkerboard” pattern; and, most significantly, they have long, piercing mouthparts that protrude from the front of the head. Additionally, Stomoxys flies will rest on surfaces in a characteristic head-upward position. Like the house fly, females tend to be larger and have more widely spaced eyes than males. Females require a blood meal just prior to egg laying and never lay eggs before their third-ever feeding (on average, a fly must feed four times before it can oviposit for the first time).
After mating the females lay their small (~1 mm long), white, sausage-shaped eggs (singly, or in bunches of 25–30) in humid areas with large amounts of decaying organic matter, such as compost piles, hay bales, spilled feed and near the edge of silage pits. As with all flies, development throughout the life cycle is temperature- and humidity-dependent, but yellowish-white larvae will generally emerge from the eggs in 1–4 days. They are typical maggots ranging in size from 5–12 mm long, and they pass through three larval instars within 10–30 (or more) days, depending on the environmental conditions. Larvae can even overwinter in livestock housing. At the end of the third instar, the larvae will move to drier sites nearby and transform into reddish-brown pupae 4–7 mm long. Adults emerge 6–20 days later. In summer, flies can complete their life cycle in 3–4 weeks.