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Horse Flies: Identification, Bite Reactions, and Clinical Management

Author(s)
Paayal S. Vora, MD
Bethany Rohr, MD

Horse flies (Tabanidae) are hematophagous dipteran insects that feed on the blood of their hosts, including humans.1 Their bites can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers and systemic illness. In this article, we discuss identifying features of horse flies as well as clinical manifestations from bite reactions, symptomatic and emergency management, and strategies for prevention and control.

Morphology and Geographic Distribution

Horse flies, which can grow as large as 30 mm, can be identified by their brown or black bodies and characteristic large heads and proboscises, wing venation, large calypters, pulvilliform empodium between large pulvilli, and lack of bristles on the body.2 Occasionally, their bodies may be gray, yellow, green, or blue, but this is less likely than in the other species of the Tabanidae family. Short hairs are present on the head and thorax. The eyes are large and often patterned, multicolored, and bright, though they also can exhibit shades of dark brown, gray, or black. There is variation in the appearance of male vs female horse flies: females have eyes that are widely spaced apart, while males have eyes that are closer together.2 It is important to note the difference between male and female horseflies, as hematophagy is exhibited only by females.1

Horse flies are found worldwide, with the exception of Hawaii, Greenland, and Iceland.3,4 They are especially prevalent in warm and moist regions, as these conditions are optimal for breeding.3-5 They tend to be active during the day and inactive at night due to a preference for sunlight and warmth.6 Due to this preference, horse flies’ seasonal activity depends on the climate; for many regions, activity persists from summer to early autumn.7

Clinical Manifestations and Treatment

Female horse flies use their mouthparts to pierce the host’s skin, inject saliva, and suck blood. The saliva contains anticoagulant properties. The bites are painful for the host, and various reactions can occur, including large urticarial wheals or papules at the site of the bite. Treatment for these minor cutaneous reactions is largely symptomatic. The bite site should be washed with soap and water; ice can be applied to help reduce inflammation.8 Oral antihistamines may be administered to reduce pruritus and treat urticaria. Topical steroids also can be prescribed for symptomatic relief. Acetaminophen and nonsteroidal anti-inflammatory drugs can be administered for pain control.8

While most cases of horse fly bites are minor, there have been reports of anaphylaxis.9 Horse fly bite–induced anaphylaxis can manifest as generalized itching, urticaria, and angioedema within minutes of being bitten. This may be followed by pharyngeal constriction, shortness of breath, nausea, vomiting, shivers, perspiration, and loss of consciousness.9 Anaphylaxis symptoms should be treated with immediate administration of intramuscular epinephrine.10

Pathogen Transmission, Prevention, and Control

Although horse flies have been found to carry numerous viruses, bacteria, and protozoa that affect other mammals, there is not enough evidence to suggest that they are vectors of transmission for humans for most diseases.11,12 In particular, West Nile virus and Borrelia burgdorferi both have been found in horse flies, but there are no reports of transmission of these diseases to humans through their bites.12

Horse flies, their close cousins deer flies (specifically Chrysops discalis), and ticks are known vectors of Francisella tularensis.13 These bacteria cause tularemia, which can manifest with symptoms such as fever, headache, and malaise. Ulceroglandular tularemia is the most common manifestation, in which the patient develops a cutaneous ulceration at the site of the horse fly bite and exhibits associated tender regional lymphadenopathy.14 Exudative conjunctivitis, exudative pharyngitis, abdominal pain, diarrhea, vomiting, and severe bilateral pneumonia also are common symptoms. The most severe form of tularemia is systemic or typhoidal tularemia, which can manifest with fever, septic shock, and hepatosplenomegaly.14 The current treatment of choice for all forms of tularemia is intravenous gentamicin, with a recommended dosage of 5 mg/kg/d for 7 to 14 days; streptomycin is an acceptable alternative.14-16 Ciprofloxacin is used less commonly and is reserved for milder disease. Incision and drainage of the affected lymph nodes also may be necessary.14 It is important to promptly identify and treat tularemia, as the mortality rate can be as high as 50% for untreated disease, especially in patients with systemic symptoms. Even after treatment, many patients exhibit residual scarring at the site of the ulcer, as well as lung, kidney, and muscle damage.14

It is advised to avoid contact with horse flies due to the range of symptom severity caused by their bites, but avoidance and control can be difficult. Malaise traps, consisting of a tent and polyester netting, can be used to capture the insects.17 Octenol has been shown to be effective for attracting horse flies and can be applied to the trap in order to increase its effectiveness.18 A Manitoba horse fly trap is a modified version of the Malaise trap that contains a suspended dark sphere to further attract horse flies.19 Patients also should be instructed to wear long-sleeved shirts and pants when outdoors in areas with horse flies to avoid contact, and application of DEET (N,N-diethylmeta-toluamide), picaridin, citronella, or geraniol-based repellents also can be effective in reducing exposure.20

Final Thoughts

Horse flies are large, blood‑feeding dipteran insects whose bites usually produce painful local reactions. Although most bites are benign, they rarely can cause anaphylaxis, and certain Tabanidae insects can transmit Francisella tularensis; therefore, clinicians should consider the risk for tularemia infection in patients presenting with horse fly bites and start appropriate antibiotic therapy when indicated. Due to the risks, prevention of bites and reduction of contact with horse flies via protective clothing, repellents, and trapping methods is recommended. Patients should be advised on bite care and to seek urgent care for systemic symptoms or rapidly progressive local signs.

References
  1. Lucas M, Krolow TK, Riet-Correa F, et al. Diversity and seasonality of horse flies (Diptera: Tabanidae) in Uruguay. Sci Rep. 2020;10:401.
  2. Chainey JE. Horse‑flies, deer‑flies and clegs (Tabanidae). In: Lane RP, Crosskey RW, eds. Medical Insects and Arachnids. Springer; 1993:310‑332.
  3. Downes JA. The post‑glacial colonization of the North Atlantic islands. Memoirs of the Entomological Society of Canada. 1988;120(S144):55‑92.
  4. Squitier JM. Deer flies, yellow flies and horse flies. Featured Creatures. University of Florida; April 1, 2014. Accessed September 15, 2023.
  5. Middlekauff WW, Lane RS. Adult and immature Tabanidae (Diptera) of California. University of California Press. 1980:1‑2.
  6. Horse flies and deer flies. University of Kentucky. Accessed September 15, 2023. https://entomology.mgcafe.uky.edu/ef511
  7. Hoover J. Horse flies. LSU College of Agriculture. May 28, 2020. Accessed May 20, 2026. https://www.lsuagcenter.com/profiles/jhoover/articles/page1590683239678
  8. Powers J, Syed HA, McDowell RH. Insect bites. StatPearls [Internet]. Updated February 15, 2026. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK537235/
  9. Hemmer W, Focke M, Vieluf D, et al. Anaphylaxis induced by horsefly bites: identification of a 69 kd IgE-binding salivary gland protein from Chrysops spp. (Diptera, Tabanidae) by Western blot analysis. J Allergy Clin Immunol. 1998;101:134-136.
  10. McLendon K, Sternard BT. Anaphylaxis. StatPearls [Internet]. Updated January 26, 2023. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK482124/
  11. Cheng TC. General Parasitology. Elsevier Science; 2012:660.
  12. Purdue Medical Entomology. Horse and deer flies. Purdue University. Accessed April 28, 2026. https://extension.entm.purdue.edu/publichealth/diseases/tabanid.html
  13. US Geological Survey. Tularemia. USGS Publications Warehouse. Accessed April 28, 2026. https://pubs.usgs.gov/circ/1297/report.pdf
  14. Snowden J, Simonsen KA. Tularemia. StatPearls [Internet]. Updated July 17, 2023. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK430905/
  15. Enderlin G, Morales L, Jacobs RF, et al. Streptomycin and alternative agents for the treatment of tularemia: review of the literature. Clin Infect Dis. 1994;19:42-47.
  16. Balestra A, Bytyci H, Guillod C, et al. A case of ulceroglandular tularemia presenting with lymphadenopathy and an ulcer on a linear morphoea lesion surrounded by erysipelas. Int Med Case Rep J. 2018;11:313-318.
  17. Malaise R. A new insect‑trap. Entomologisk Tidskrift. 1937;58:148‑160.
  18. French F, Kline D. l-Octen-3-ol, an effective attractant for Tabanidae (Diptera). J Med Entomol. 1989;26:459-461
  19. Axtell RC, Edwards TD, Dukes JC. Rigid canopy trap for Tabanidae (Diptera). J Georgia Entomol Soc. 1975;10: 64-67.
  20. Squitier JM. Deer flies, yellow flies and horse flies. Featured Creatures. University of Florida. April 1, 2014. Accessed May 12, 2026. https://ask.ifas.ufl.edu/publication/IN155

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Author and Disclosure Information

Dr. Vora is from the Department of Dermatology, HealthPartners Institute, Minneapolis, Minnesota, and University Hospitals Community Consortium, Chardon, Ohio. Dr. Rohr is from the Department of Dermatology, Case Western University Hospitals, Cleveland, Ohio.

The authors have no relevant financial disclosures to report.

Correspondence: Paayal S. Vora, MD (pvora@neomed.edu).

Cutis. 2026 June;117(6):186-187. doi:10.12788/cutis.1398

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Author(s)
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Bethany Rohr, MD
Author(s)
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Bethany Rohr, MD
Author and Disclosure Information

Dr. Vora is from the Department of Dermatology, HealthPartners Institute, Minneapolis, Minnesota, and University Hospitals Community Consortium, Chardon, Ohio. Dr. Rohr is from the Department of Dermatology, Case Western University Hospitals, Cleveland, Ohio.

The authors have no relevant financial disclosures to report.

Correspondence: Paayal S. Vora, MD (pvora@neomed.edu).

Cutis. 2026 June;117(6):186-187. doi:10.12788/cutis.1398

Author and Disclosure Information

Dr. Vora is from the Department of Dermatology, HealthPartners Institute, Minneapolis, Minnesota, and University Hospitals Community Consortium, Chardon, Ohio. Dr. Rohr is from the Department of Dermatology, Case Western University Hospitals, Cleveland, Ohio.

The authors have no relevant financial disclosures to report.

Correspondence: Paayal S. Vora, MD (pvora@neomed.edu).

Cutis. 2026 June;117(6):186-187. doi:10.12788/cutis.1398

Article PDF
CT117006186.pdf
Article PDF
CT117006186.pdf

Horse flies (Tabanidae) are hematophagous dipteran insects that feed on the blood of their hosts, including humans.1 Their bites can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers and systemic illness. In this article, we discuss identifying features of horse flies as well as clinical manifestations from bite reactions, symptomatic and emergency management, and strategies for prevention and control.

Morphology and Geographic Distribution

Horse flies, which can grow as large as 30 mm, can be identified by their brown or black bodies and characteristic large heads and proboscises, wing venation, large calypters, pulvilliform empodium between large pulvilli, and lack of bristles on the body.2 Occasionally, their bodies may be gray, yellow, green, or blue, but this is less likely than in the other species of the Tabanidae family. Short hairs are present on the head and thorax. The eyes are large and often patterned, multicolored, and bright, though they also can exhibit shades of dark brown, gray, or black. There is variation in the appearance of male vs female horse flies: females have eyes that are widely spaced apart, while males have eyes that are closer together.2 It is important to note the difference between male and female horseflies, as hematophagy is exhibited only by females.1

Horse flies are found worldwide, with the exception of Hawaii, Greenland, and Iceland.3,4 They are especially prevalent in warm and moist regions, as these conditions are optimal for breeding.3-5 They tend to be active during the day and inactive at night due to a preference for sunlight and warmth.6 Due to this preference, horse flies’ seasonal activity depends on the climate; for many regions, activity persists from summer to early autumn.7

Clinical Manifestations and Treatment

Female horse flies use their mouthparts to pierce the host’s skin, inject saliva, and suck blood. The saliva contains anticoagulant properties. The bites are painful for the host, and various reactions can occur, including large urticarial wheals or papules at the site of the bite. Treatment for these minor cutaneous reactions is largely symptomatic. The bite site should be washed with soap and water; ice can be applied to help reduce inflammation.8 Oral antihistamines may be administered to reduce pruritus and treat urticaria. Topical steroids also can be prescribed for symptomatic relief. Acetaminophen and nonsteroidal anti-inflammatory drugs can be administered for pain control.8

While most cases of horse fly bites are minor, there have been reports of anaphylaxis.9 Horse fly bite–induced anaphylaxis can manifest as generalized itching, urticaria, and angioedema within minutes of being bitten. This may be followed by pharyngeal constriction, shortness of breath, nausea, vomiting, shivers, perspiration, and loss of consciousness.9 Anaphylaxis symptoms should be treated with immediate administration of intramuscular epinephrine.10

Pathogen Transmission, Prevention, and Control

Although horse flies have been found to carry numerous viruses, bacteria, and protozoa that affect other mammals, there is not enough evidence to suggest that they are vectors of transmission for humans for most diseases.11,12 In particular, West Nile virus and Borrelia burgdorferi both have been found in horse flies, but there are no reports of transmission of these diseases to humans through their bites.12

Horse flies, their close cousins deer flies (specifically Chrysops discalis), and ticks are known vectors of Francisella tularensis.13 These bacteria cause tularemia, which can manifest with symptoms such as fever, headache, and malaise. Ulceroglandular tularemia is the most common manifestation, in which the patient develops a cutaneous ulceration at the site of the horse fly bite and exhibits associated tender regional lymphadenopathy.14 Exudative conjunctivitis, exudative pharyngitis, abdominal pain, diarrhea, vomiting, and severe bilateral pneumonia also are common symptoms. The most severe form of tularemia is systemic or typhoidal tularemia, which can manifest with fever, septic shock, and hepatosplenomegaly.14 The current treatment of choice for all forms of tularemia is intravenous gentamicin, with a recommended dosage of 5 mg/kg/d for 7 to 14 days; streptomycin is an acceptable alternative.14-16 Ciprofloxacin is used less commonly and is reserved for milder disease. Incision and drainage of the affected lymph nodes also may be necessary.14 It is important to promptly identify and treat tularemia, as the mortality rate can be as high as 50% for untreated disease, especially in patients with systemic symptoms. Even after treatment, many patients exhibit residual scarring at the site of the ulcer, as well as lung, kidney, and muscle damage.14

It is advised to avoid contact with horse flies due to the range of symptom severity caused by their bites, but avoidance and control can be difficult. Malaise traps, consisting of a tent and polyester netting, can be used to capture the insects.17 Octenol has been shown to be effective for attracting horse flies and can be applied to the trap in order to increase its effectiveness.18 A Manitoba horse fly trap is a modified version of the Malaise trap that contains a suspended dark sphere to further attract horse flies.19 Patients also should be instructed to wear long-sleeved shirts and pants when outdoors in areas with horse flies to avoid contact, and application of DEET (N,N-diethylmeta-toluamide), picaridin, citronella, or geraniol-based repellents also can be effective in reducing exposure.20

Final Thoughts

Horse flies are large, blood‑feeding dipteran insects whose bites usually produce painful local reactions. Although most bites are benign, they rarely can cause anaphylaxis, and certain Tabanidae insects can transmit Francisella tularensis; therefore, clinicians should consider the risk for tularemia infection in patients presenting with horse fly bites and start appropriate antibiotic therapy when indicated. Due to the risks, prevention of bites and reduction of contact with horse flies via protective clothing, repellents, and trapping methods is recommended. Patients should be advised on bite care and to seek urgent care for systemic symptoms or rapidly progressive local signs.

Horse flies (Tabanidae) are hematophagous dipteran insects that feed on the blood of their hosts, including humans.1 Their bites can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers and systemic illness. In this article, we discuss identifying features of horse flies as well as clinical manifestations from bite reactions, symptomatic and emergency management, and strategies for prevention and control.

Morphology and Geographic Distribution

Horse flies, which can grow as large as 30 mm, can be identified by their brown or black bodies and characteristic large heads and proboscises, wing venation, large calypters, pulvilliform empodium between large pulvilli, and lack of bristles on the body.2 Occasionally, their bodies may be gray, yellow, green, or blue, but this is less likely than in the other species of the Tabanidae family. Short hairs are present on the head and thorax. The eyes are large and often patterned, multicolored, and bright, though they also can exhibit shades of dark brown, gray, or black. There is variation in the appearance of male vs female horse flies: females have eyes that are widely spaced apart, while males have eyes that are closer together.2 It is important to note the difference between male and female horseflies, as hematophagy is exhibited only by females.1

Horse flies are found worldwide, with the exception of Hawaii, Greenland, and Iceland.3,4 They are especially prevalent in warm and moist regions, as these conditions are optimal for breeding.3-5 They tend to be active during the day and inactive at night due to a preference for sunlight and warmth.6 Due to this preference, horse flies’ seasonal activity depends on the climate; for many regions, activity persists from summer to early autumn.7

Clinical Manifestations and Treatment

Female horse flies use their mouthparts to pierce the host’s skin, inject saliva, and suck blood. The saliva contains anticoagulant properties. The bites are painful for the host, and various reactions can occur, including large urticarial wheals or papules at the site of the bite. Treatment for these minor cutaneous reactions is largely symptomatic. The bite site should be washed with soap and water; ice can be applied to help reduce inflammation.8 Oral antihistamines may be administered to reduce pruritus and treat urticaria. Topical steroids also can be prescribed for symptomatic relief. Acetaminophen and nonsteroidal anti-inflammatory drugs can be administered for pain control.8

While most cases of horse fly bites are minor, there have been reports of anaphylaxis.9 Horse fly bite–induced anaphylaxis can manifest as generalized itching, urticaria, and angioedema within minutes of being bitten. This may be followed by pharyngeal constriction, shortness of breath, nausea, vomiting, shivers, perspiration, and loss of consciousness.9 Anaphylaxis symptoms should be treated with immediate administration of intramuscular epinephrine.10

Pathogen Transmission, Prevention, and Control

Although horse flies have been found to carry numerous viruses, bacteria, and protozoa that affect other mammals, there is not enough evidence to suggest that they are vectors of transmission for humans for most diseases.11,12 In particular, West Nile virus and Borrelia burgdorferi both have been found in horse flies, but there are no reports of transmission of these diseases to humans through their bites.12

Horse flies, their close cousins deer flies (specifically Chrysops discalis), and ticks are known vectors of Francisella tularensis.13 These bacteria cause tularemia, which can manifest with symptoms such as fever, headache, and malaise. Ulceroglandular tularemia is the most common manifestation, in which the patient develops a cutaneous ulceration at the site of the horse fly bite and exhibits associated tender regional lymphadenopathy.14 Exudative conjunctivitis, exudative pharyngitis, abdominal pain, diarrhea, vomiting, and severe bilateral pneumonia also are common symptoms. The most severe form of tularemia is systemic or typhoidal tularemia, which can manifest with fever, septic shock, and hepatosplenomegaly.14 The current treatment of choice for all forms of tularemia is intravenous gentamicin, with a recommended dosage of 5 mg/kg/d for 7 to 14 days; streptomycin is an acceptable alternative.14-16 Ciprofloxacin is used less commonly and is reserved for milder disease. Incision and drainage of the affected lymph nodes also may be necessary.14 It is important to promptly identify and treat tularemia, as the mortality rate can be as high as 50% for untreated disease, especially in patients with systemic symptoms. Even after treatment, many patients exhibit residual scarring at the site of the ulcer, as well as lung, kidney, and muscle damage.14

It is advised to avoid contact with horse flies due to the range of symptom severity caused by their bites, but avoidance and control can be difficult. Malaise traps, consisting of a tent and polyester netting, can be used to capture the insects.17 Octenol has been shown to be effective for attracting horse flies and can be applied to the trap in order to increase its effectiveness.18 A Manitoba horse fly trap is a modified version of the Malaise trap that contains a suspended dark sphere to further attract horse flies.19 Patients also should be instructed to wear long-sleeved shirts and pants when outdoors in areas with horse flies to avoid contact, and application of DEET (N,N-diethylmeta-toluamide), picaridin, citronella, or geraniol-based repellents also can be effective in reducing exposure.20

Final Thoughts

Horse flies are large, blood‑feeding dipteran insects whose bites usually produce painful local reactions. Although most bites are benign, they rarely can cause anaphylaxis, and certain Tabanidae insects can transmit Francisella tularensis; therefore, clinicians should consider the risk for tularemia infection in patients presenting with horse fly bites and start appropriate antibiotic therapy when indicated. Due to the risks, prevention of bites and reduction of contact with horse flies via protective clothing, repellents, and trapping methods is recommended. Patients should be advised on bite care and to seek urgent care for systemic symptoms or rapidly progressive local signs.

References
  1. Lucas M, Krolow TK, Riet-Correa F, et al. Diversity and seasonality of horse flies (Diptera: Tabanidae) in Uruguay. Sci Rep. 2020;10:401.
  2. Chainey JE. Horse‑flies, deer‑flies and clegs (Tabanidae). In: Lane RP, Crosskey RW, eds. Medical Insects and Arachnids. Springer; 1993:310‑332.
  3. Downes JA. The post‑glacial colonization of the North Atlantic islands. Memoirs of the Entomological Society of Canada. 1988;120(S144):55‑92.
  4. Squitier JM. Deer flies, yellow flies and horse flies. Featured Creatures. University of Florida; April 1, 2014. Accessed September 15, 2023.
  5. Middlekauff WW, Lane RS. Adult and immature Tabanidae (Diptera) of California. University of California Press. 1980:1‑2.
  6. Horse flies and deer flies. University of Kentucky. Accessed September 15, 2023. https://entomology.mgcafe.uky.edu/ef511
  7. Hoover J. Horse flies. LSU College of Agriculture. May 28, 2020. Accessed May 20, 2026. https://www.lsuagcenter.com/profiles/jhoover/articles/page1590683239678
  8. Powers J, Syed HA, McDowell RH. Insect bites. StatPearls [Internet]. Updated February 15, 2026. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK537235/
  9. Hemmer W, Focke M, Vieluf D, et al. Anaphylaxis induced by horsefly bites: identification of a 69 kd IgE-binding salivary gland protein from Chrysops spp. (Diptera, Tabanidae) by Western blot analysis. J Allergy Clin Immunol. 1998;101:134-136.
  10. McLendon K, Sternard BT. Anaphylaxis. StatPearls [Internet]. Updated January 26, 2023. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK482124/
  11. Cheng TC. General Parasitology. Elsevier Science; 2012:660.
  12. Purdue Medical Entomology. Horse and deer flies. Purdue University. Accessed April 28, 2026. https://extension.entm.purdue.edu/publichealth/diseases/tabanid.html
  13. US Geological Survey. Tularemia. USGS Publications Warehouse. Accessed April 28, 2026. https://pubs.usgs.gov/circ/1297/report.pdf
  14. Snowden J, Simonsen KA. Tularemia. StatPearls [Internet]. Updated July 17, 2023. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK430905/
  15. Enderlin G, Morales L, Jacobs RF, et al. Streptomycin and alternative agents for the treatment of tularemia: review of the literature. Clin Infect Dis. 1994;19:42-47.
  16. Balestra A, Bytyci H, Guillod C, et al. A case of ulceroglandular tularemia presenting with lymphadenopathy and an ulcer on a linear morphoea lesion surrounded by erysipelas. Int Med Case Rep J. 2018;11:313-318.
  17. Malaise R. A new insect‑trap. Entomologisk Tidskrift. 1937;58:148‑160.
  18. French F, Kline D. l-Octen-3-ol, an effective attractant for Tabanidae (Diptera). J Med Entomol. 1989;26:459-461
  19. Axtell RC, Edwards TD, Dukes JC. Rigid canopy trap for Tabanidae (Diptera). J Georgia Entomol Soc. 1975;10: 64-67.
  20. Squitier JM. Deer flies, yellow flies and horse flies. Featured Creatures. University of Florida. April 1, 2014. Accessed May 12, 2026. https://ask.ifas.ufl.edu/publication/IN155

References
  1. Lucas M, Krolow TK, Riet-Correa F, et al. Diversity and seasonality of horse flies (Diptera: Tabanidae) in Uruguay. Sci Rep. 2020;10:401.
  2. Chainey JE. Horse‑flies, deer‑flies and clegs (Tabanidae). In: Lane RP, Crosskey RW, eds. Medical Insects and Arachnids. Springer; 1993:310‑332.
  3. Downes JA. The post‑glacial colonization of the North Atlantic islands. Memoirs of the Entomological Society of Canada. 1988;120(S144):55‑92.
  4. Squitier JM. Deer flies, yellow flies and horse flies. Featured Creatures. University of Florida; April 1, 2014. Accessed September 15, 2023.
  5. Middlekauff WW, Lane RS. Adult and immature Tabanidae (Diptera) of California. University of California Press. 1980:1‑2.
  6. Horse flies and deer flies. University of Kentucky. Accessed September 15, 2023. https://entomology.mgcafe.uky.edu/ef511
  7. Hoover J. Horse flies. LSU College of Agriculture. May 28, 2020. Accessed May 20, 2026. https://www.lsuagcenter.com/profiles/jhoover/articles/page1590683239678
  8. Powers J, Syed HA, McDowell RH. Insect bites. StatPearls [Internet]. Updated February 15, 2026. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK537235/
  9. Hemmer W, Focke M, Vieluf D, et al. Anaphylaxis induced by horsefly bites: identification of a 69 kd IgE-binding salivary gland protein from Chrysops spp. (Diptera, Tabanidae) by Western blot analysis. J Allergy Clin Immunol. 1998;101:134-136.
  10. McLendon K, Sternard BT. Anaphylaxis. StatPearls [Internet]. Updated January 26, 2023. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK482124/
  11. Cheng TC. General Parasitology. Elsevier Science; 2012:660.
  12. Purdue Medical Entomology. Horse and deer flies. Purdue University. Accessed April 28, 2026. https://extension.entm.purdue.edu/publichealth/diseases/tabanid.html
  13. US Geological Survey. Tularemia. USGS Publications Warehouse. Accessed April 28, 2026. https://pubs.usgs.gov/circ/1297/report.pdf
  14. Snowden J, Simonsen KA. Tularemia. StatPearls [Internet]. Updated July 17, 2023. Accessed May 12, 2026. https://www.ncbi.nlm.nih.gov/books/NBK430905/
  15. Enderlin G, Morales L, Jacobs RF, et al. Streptomycin and alternative agents for the treatment of tularemia: review of the literature. Clin Infect Dis. 1994;19:42-47.
  16. Balestra A, Bytyci H, Guillod C, et al. A case of ulceroglandular tularemia presenting with lymphadenopathy and an ulcer on a linear morphoea lesion surrounded by erysipelas. Int Med Case Rep J. 2018;11:313-318.
  17. Malaise R. A new insect‑trap. Entomologisk Tidskrift. 1937;58:148‑160.
  18. French F, Kline D. l-Octen-3-ol, an effective attractant for Tabanidae (Diptera). J Med Entomol. 1989;26:459-461
  19. Axtell RC, Edwards TD, Dukes JC. Rigid canopy trap for Tabanidae (Diptera). J Georgia Entomol Soc. 1975;10: 64-67.
  20. Squitier JM. Deer flies, yellow flies and horse flies. Featured Creatures. University of Florida. April 1, 2014. Accessed May 12, 2026. https://ask.ifas.ufl.edu/publication/IN155

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Horse Flies: Identification, Bite Reactions, and Clinical Management

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  • Horse flies (Tabanidae) are hematophagous insects that can cause minor cutaneous reactions (eg, urticaria) or, rarely, severe reactions such as anaphylaxis. They also are vectors of tularemia, which may manifest with cutaneous ulcers or systemic illness.
  • Mild reactions are managed symptomatically; anaphylaxis requires epinephrine, and tularemia requires systemic antibiotics such as gentamicin.
  • Patients should be counseled on avoidance strategies, including wearing protective clothing and using topical repellents and environmental traps.
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