The stable fly, Stomoxys calcitrans, is often mistaken for the common house fly. Unlike its non-biting relative, the stable fly is a serious nuisance because both males and females possess a hardened, needle-like mouthpart used to inflict a painful bite on warm-blooded animals, including humans and livestock. These flies feed multiple times a day, primarily targeting the lower legs and ankles of their hosts. This causes significant irritation, reduced productivity in animals, and considerable discomfort to people. Eliminating a stable fly problem requires a multi-faceted approach focused on disrupting their life cycle, starting with proper identification and understanding their habits.
Identifying Stable Flies and Their Habits
Distinguishing the stable fly from the house fly is the first step toward effective control, as misidentification leads to ineffective treatment strategies. The most defining feature of the stable fly is its rigid, bayonet-like proboscis, which protrudes horizontally forward from the head, even when the fly is at rest. House flies, conversely, have sponging mouthparts that are not visible in the same way.
Stable flies are typically grayish-brown and similar in size to a house fly, but they have four dark stripes on their thorax and a distinctive checkerboard pattern on their abdomen. When resting, they often assume a head-upward posture on vertical surfaces like walls or fences, unlike house flies which may rest head-down. Their behavior is characterized by feeding on blood for several minutes before quickly flying off to rest and digest, often attacking the lower limbs of their hosts.
Eliminating Breeding Sites
Controlling stable flies is primarily dependent on sanitation, as the larvae develop exclusively in moist, decaying organic matter. This source reduction approach is the most effective method, potentially achieving up to 90% control. Female flies lay eggs in materials that are wet and fermenting, such as decaying straw, spilled silage, old hay, grass clippings, and manure mixed with bedding.
Actionable sanitation involves the immediate removal and proper management of these materials to prevent the environment from supporting larval development. Spreading out wet organic matter into a thin layer allows it to dry quickly, making it unsuitable for egg-laying and larval survival. Manure should be removed weekly or stockpiled and covered with plastic to prevent it from getting wet and attracting flies.
Repairing leaky water troughs, pipes, and other sources of moisture is also necessary to eliminate damp areas where organic material can accumulate and decompose. Where complete removal of organic matter is not feasible, a larvicide can be applied to target the developing maggots in the breeding medium. These treatments prevent the larvae from maturing into adult flies, breaking the reproductive cycle at its source.
Immediate Control of Adult Flies
While sanitation addresses the source, immediate relief from the current adult population is necessary, using methods that complement habitat control. Adult stable flies are attracted to certain visual cues, which can be exploited using specialized traps. Visual traps, often blue or black sticky panels, work by attracting the flies to contrasting colors where they become caught on the adhesive surface.
Placing these visual traps in sunny areas near where the flies rest, such as along fences or the exterior of barns, can help reduce the biting adult population. However, these traps only capture flies actively seeking a host or resting, offering temporary relief without addressing the underlying breeding problem.
Insecticides can be used as a space spray for quick knockdown or as a residual spray on surfaces where flies rest. Stable flies tend to rest on the shady sides of buildings, feed bunks, and windbreaks, making these areas prime targets for residual applications. Safety precautions are paramount, requiring careful adherence to label instructions, especially regarding application around animals, food, and people. Chemical control is often short-lived and should be used to suppress populations while long-term sanitation takes effect.
Ongoing Exclusion Strategies
Maintaining a long-term strategy involves continuous environmental management and the introduction of biological controls to keep stable fly populations suppressed. Physical barriers, such as fine-mesh screening on doors and windows of homes, barns, or kennels, prevent adult flies from entering sensitive areas. Simple tools like fans can also be used to create air movement, making it difficult for the flies to land and feed.
A highly effective, long-term biological control method involves the use of parasitic wasps, often referred to commercially as fly parasites or fly predators. These tiny, non-stinging wasps are natural enemies of stable flies. They lay their eggs inside the stable fly pupae, and the developing wasp larvae consume the pupa, preventing the emergence of a new adult fly and breaking the reproductive cycle.
Releasing these wasps in a consistent, seasonal program is a preventative measure that targets the pupal stage in breeding materials, offering a sustainable alternative to chemical use. This biological approach, combined with the year-round commitment to keeping all organic materials dry and clean, ensures the environment remains inhospitable to stable fly development and prevents future infestations.