Horsefly bite: symptoms, dangerous, risk of allergy, what to do?

Horseflies don’t get a bad reputation for nothing. These large fly-like insects are mainly found in warm regions, or close to bodies of water. Contrary to popular belief, horseflies do not sting, but bite : they tear off small pieces of flesh to insert their formidable trunk and gorge themselves on blood, lymph and skin debris. Hence the pain felt. How to react in the event of a bite? What are the risks ?

The horsefly looks like a large flat fly, dark brown in color, turning yellow. It belongs to the family of Tabanidae, of the order Diptera, a large class of insects. It feeds mainly on other aquatic insects, molluscs, crustaceans or organic detritus. This is why it is most often found near lakes and rivers, mainly in summer (from the end of May until the beginning of September).

© iStock / dmastak80

Why does a horsefly bite?

Important information: male horseflies are harmless, they do not bite. Only female horseflies need to suck blood to replenish their energy and allow their eggs to develop. Hence the bites. They therefore set their sights on other species that cross their path. Most of the time, it is cattle or horses, but sometimes they bite nearby humans. They also forage flower nectar to complement their meal.

What are the symptoms after a horsefly bite?

Horsefly bites cause severe pain, which is accompanied by localized inflammation. We then observe the formation of a red plaque at the level of the bite. Not only does it itch, but it also quickly becomes hot and swollen.

How long do these symptoms last?

The pain is particularly sharp, but remains transient. In the vast majority of cases, the symptoms related to the horsefly bite will disappear spontaneously, after a few hours. If they persist for more than a day or two, see a doctor!

Horsefly bite and allergy: what are the risks?

In some – rather rare – cases the horsefly bite can cause allergic reactions. Victims develop almost instantaneous symptoms, such as:

Unfortunately, there is no specific desensitization treatment for horseflies. If in doubt after a bite, don’t waste a minute: contact the emergency services (15, 18 or 112). If possible, quickly inject adrenaline therapy via an auto-injector pen.

Note: even more rarely, a horsefly bite carrying bacteria, viruses or parasites can transmit infectious diseases. Hence the importance of consulting in the face of severe and/or persistent symptoms!

Horseflies love wet skin. They are also attracted to dark colored objects and carbon dioxide fumes that occur during activities such as mowing, sawing or mechanical weeding. These few tips will allow you to limit the attacks of the formidable females:

  • dry yourself quickly after swimming ;
  • avoid loose clothingwhich would allow insects to get in, get stuck and bite you;
  • prefer light-colored clothes : like mosquitoes, horseflies are attracted to dark colors (blue, black and red), which allow them to camouflage themselves more easily;
  • some insect repellents can also be useful in repelling horseflies.

If you are going on an adventure and you are likely to come across water points or animals such as cows, sheep or horses, prefer light and breathable clothing, that completely cover your arms and legs.

The female horsefly tears off the skin using her mandibles. She has no stinger, don’t waste your time trying to remove it with tweezers. In the event of a bite, the first reflex is to disinfect the affected area with an alcohol swab. If necessary, opt for an antiseptic solution (Biseptine, Hexomedine, etc.), or clean it with water and mild soap.

If necessary, to calm the pain, take an oral painkiller (Doliprane, Efferalgan, etc.), taking care to respect the dosage. Avoid scratching as much as possible, so as not to risk infecting the bite. Antihistamines (in gel, or orally) can be taken as a supplement to reduce itching and local edema. Of the cortisone ointmentslow dose, are also available in pharmacies, without a prescription.

Horsefly bite: what to avoid?

In the event of an insect bite, never apply ice cubes for pain relief : the cold risks congealing the venom.

Essential oils are also not recommended, not only because of the allergic risks, but also because the skin is abraded and fragile.

How to react if the bite swells or does not heal?

If the symptoms worsen, or persist in spite of the treatments administered, consult a doctor quickly, responsible for redoing the point. In the event of a moderate allergic reaction or associated symptoms, he may adapt the treatment and prescribe topical corticosteroids. If in doubt, he may order a blood test to check that the horsefly has not transmitted any infectious disease.