Chances are you’ve been bitten by a horsefly on more than one occasion.

If you’re not immediately familiar with this pesky insect, it’s a large, dark fly. You can generally recognize it by its size. A horsefly can be as long as 1 inch (2.54 centimeters), making it much larger than the average fly.

Read on to find out what you should do if a horsefly bites you.

If you’ve ever been bitten by a horsefly, you know that it hurts.

The fly’s mandible is what makes these bites so painful. The mandible is essentially the insect’s jaw. It’s shaped like scissors and can cut right into the skin.

The mandible is also equipped with small hooks to help the horsefly lock in to feed better. Once the horsefly is locked in, it eats the blood from the skin.

This bite can cause:

Aside from the momentary pain they cause, horsefly bites are not generally harmful to humans. These bites are usually only a problem for horses.

This is because horseflies carry equine infectious anemia, also known as swamp fever. When they bite an equine animal, they can transmit this life threatening disease.

If infected, a horse may experience a fever, hemorrhaging, and general illness. Some horses do not experience any symptoms, but they may still transmit the disease to other equine animals.

Horseflies are found throughout North America. They are highly concentrated in hot, humid states, such as Florida. In some regions, horseflies are pretty much unavoidable, especially in the summer months.

Horseflies are most active during the daylight hours, particularly in the summer. They attack large mammals, such as humans, dogs, and, of course, horses.

They’re most attracted to moving objects and dark objects. They’re also attracted to carbon dioxide. This may explain why all of those outdoor summer activities that get you sweating and breathing heavy seem to bring out the horseflies.

If you’ve ever thought that a horsefly was out for vengeance, you may be right. Pest World states that female horseflies in particular are very persistent. They’ve been known to chase their victims for a short time if their first bite does not get them the satisfying meal they were hoping for.

Horseflies can be distinguished by their color.

The upper part of a horsefly is white and typically marked by a few vertical black lines. The lower segment of the fly is solid black.

Cleanse the bite and apply over-the-counter antiseptic spray or ointment to help keep the wound clean and decrease irritation and itchiness. In most cases, a horsefly bite can heal on its own in a few days.

Be sure to watch the area for signs of an infection, such as excessive pus or a foul odor. If you have any unusual symptoms, consult a doctor.

Certain insect bites can cause more serious reactions. If you have difficulty breathing, a rash that spreads, or worsening pain, seek medical attention.

If you’ve been bitten by a horsefly, the bite will generally heal in a matter of days. You typically will not experience any adverse side effects.

If your bite has not healed within 1 week, or if you’re experiencing unusual symptoms such as dizziness or worsening pain, consult a doctor. They can assess your bite and determine any next steps.

To prevent future horsefly bites, apply insect repellent before going outdoors. If possible, stick to light-colored clothing. Horseflies are attracted to darker colors, so this may help keep them away.