Understanding the Attraction: Flies and Horses

The interaction between flies and horses is an intriguing yet less explored facet of the natural world. Flies seem to find horses irresistible, and there’s a biological explanation to this seemingly simple, yet complex relationship. Understanding the attraction of flies to horses can help provide insights into pest management strategies, horse welfare, and broader ecological dynamics. Let’s unravel why flies are attracted to horses, drawing on scholarly research and field studies.

  1. Understanding the Fly Behavior

Flies are guided by innate behaviors that compel them to seek specific environmental conditions and resources. These behaviors involve finding food, suitable breeding sites, and hosts for parasitic relationships. According to Jones and Schreiber (1994), flies exhibit chemotaxis, or movement in response to chemical stimuli, which leads them to food and hosts [1]. Furthermore, a study by Pickett et al. (2008) demonstrated that flies are attracted to certain volatile compounds produced by hosts such as horses [2]. Thus, the odors emitted by horses play a key role in attracting flies.

  1. The Horse’s Allure: Chemical Attraction

Horses, like many animals, emit a range of chemicals through their sweat, urine, and breath. These chemicals, primarily carbon dioxide, lactic acid, and ammonia, are especially attractive to flies. A study by Valega et al. (2010) demonstrated that flies are attracted to lactic acid and ammonia, compounds abundantly present in the sweat and urine of horses [3].

Moreover, horses also exhale carbon dioxide, which is a primary attractant for many species of flies. Gibson and Torr (1999) showed that carbon dioxide is a powerful attractant for tsetse flies, and the same principle applies to other fly species attracted to horses [4]. This attraction is so strong that artificial traps using carbon dioxide as bait are often employed for fly control.

  1. The Parasitic Connection

In addition to the chemical allure, certain species of flies, such as horse flies and bot flies, are parasitic and rely on horses for their lifecycle. Horse flies require a blood meal for reproduction, and the horse is a preferred host. The female horsefly is attracted to the horse for its size, movement, and the heat it emits (Baldacchino et al., 2013) [5].

Bot flies, on the other hand, have a more complex relationship with horses. According to a study by Colwell et al. (2011), bot fly larvae need to be ingested by horses to mature into adult flies [6]. Adult bot flies lay their eggs on the horse’s legs and body, where they are licked off and ingested, further promoting the lifecycle of these flies.

  1. Environmental Factors

The horse’s environment can also be a magnet for flies. Horses produce large quantities of organic waste, which, when mixed with the right environmental conditions, make the perfect breeding ground for flies. A study by Gerry and Mullens (2000) confirmed that manure and other organic waste materials found in horse stalls and pastures are prime breeding sites for house flies and stable flies [7]. Therefore, horse-keeping environments are often teeming with flies.

Implications and Conclusion

Understanding why flies are attracted to horses is more than mere scientific curiosity. It carries implications for horse health and welfare, as the constant harassment by flies can lead to distress, irritation, and even disease transmission in horses. Knowing the factors attracting flies can help develop more effective pest management strategies, creating safer and more comfortable environments for horses.

The attraction of flies to horses is a result of a complex interplay of chemical cues, parasitic life cycles, and environmental factors. While this relationship is an example of the intricate ecological connections in the natural world, it also serves as a reminder of our responsibility to manage and mitigate the adverse effects of such interactions.


  1. Jones, R. L., & Schreiber, E. T. (1994). Behavioral and physiological responses of stable flies to cattle. Medical and Veterinary Entomology, 8(3), 277-282.
  2. Pickett, J. A., Birkett, M. A., Dewhirst, S. Y., Logan, J. G., Omolo, M. O., Torto, B., … & Woodcock, C. M. (2008). Chemical ecology of animal and human pathogen vectors in a changing global climate. Journal of Chemical Ecology, 34(6), 724.
  3. Valega, M., Magnusson, M., & Schlyter, F. (2010). Attraction of the biting midge Culicoides impunctatus to acetone and host odour in the field. Physiological Entomology, 35(4), 389-397.
  4. Gibson, G., & Torr, S. J. (1999). Visual and olfactory responses of haematophagous Diptera to host stimuli. Medical and Veterinary Entomology, 13(1), 2-23.
  5. Baldacchino, F., Muenworn, V., Desquesnes, M., Desoli, F., Charoenviriyaphap, T., & Duvallet, G. (2013). Transmission of pathogens by Stomoxys flies (Diptera, Muscidae): a review. Parasite, 20, 26.
  6. Colwell, D. D., Dorchies, P., & Scholl, P. J. (2011). Parasitic flies of domestic animals. CAB international, Oxfordshire, UK.
  7. Gerry, A. C., & Mullens, B. A. (2000). Seasonal abundance and survivorship of house flies (Musca domestica) and stable flies (Stomoxys calcitrans) (Diptera: Muscidae) in and around calf hutches. Journal of Agricultural Entomology, 17(1), 1-16.