Flies are commonly seen congregating around cattle in pastures and barns. This persistent attraction is not accidental; it stems from biological factors that make cows highly desirable hosts and breeding grounds for numerous fly species. Understanding these specific attractants reveals why flies are so drawn to these large animals, from bodily secretions to environmental factors, and their impact on cattle well-being and productivity.
Bovine Secretions and Blood Meals
Cows produce a variety of bodily fluids that serve as attractive food sources for many fly species. Tears, mucus around the eyes and nostrils, and saliva are particularly appealing due to their nutrient content, moisture, and proteins. Face flies, for instance, are known to feed on these secretions, with females particularly seeking protein for egg development.
Beyond surface secretions, certain flies are drawn to blood meals. Stable flies and horn flies, equipped with piercing mouthparts, feed on blood. Stable flies inflict painful bites, often targeting the legs and lower body. Horn flies cluster on the back and sides, taking multiple blood meals daily. Open wounds on cattle can also attract blood-feeding flies.
Manure and Methane Emissions
Cattle manure is a primary breeding ground and food source for many fly species, including house flies and face flies. Flies are highly attracted to the decomposition process in fresh manure for egg-laying. This decomposition releases various volatile organic compounds, such as p-cresol and phenol, which are potent olfactory cues for adult flies. House flies, for example, develop in fresh manure or decaying organic matter mixed with manure, soil, and moisture.
While not a direct food source, methane and other gases emitted by cows also play a role in fly attraction. Research indicates that certain gases, including carbon dioxide and methane, can attract host-seeking stable flies, particularly when present in combination. This suggests the overall gaseous profile from a cow and its environment contributes to its attractiveness.
Body Heat and Carbon Dioxide
The substantial body mass of a cow generates significant heat, making them a warm target for flies, especially in cooler conditions. Flies are often more active when temperatures are high and winds are low, seeking out warm hosts. This thermal signature serves as a long-range cue for many insect species. The cow’s size also provides an expansive surface area for flies to land, rest, and feed.
Cows continuously exhale carbon dioxide (CO2), a powerful attractant for many fly species, including mosquitoes and various biting flies. Flies possess specialized sensory organs that detect CO2 plumes, using this gas to locate potential hosts and activate host-seeking behavior. This exhalation, combined with other host factors like warmth and odor, forms a complex sensory signal for flies.
Consequences for Cattle Health and Productivity
The constant presence of flies challenges cattle health and productivity. Fly infestations cause irritation and stress, leading to defensive behaviors like head-shaking, tail-switching, and stomping. This annoyance can reduce feeding time and disrupt grazing, potentially resulting in weight loss and decreased milk production. For instance, stable flies can cause significant production losses, including reduced milk yield in dairy cows and decreased weight gain in beef cattle.
Flies are also vectors for various diseases, transmitting pathogens between animals. Pinkeye (infectious bovine keratoconjunctivitis), a painful and contagious bacterial eye disease, is commonly spread by face flies. Other diseases that can be mechanically transmitted by flies include anaplasmosis, summer mastitis, and bovine respiratory disease pathogens. The economic impact of fly infestations on the cattle industry is considerable, with estimated annual losses in the United States reaching billions of dollars.