What to Know About Deer Flies

Medically Reviewed by Jabeen Begum, MD on November 30, 2022
4 min read

Deer flies, sometimes grouped with horseflies or moose flies, are small flying insects with painful bites found all over the world. This kind of fly is persistent and leaves behind annoying, itchy bites that linger.

What are deer flies? They are blood-sucking pests that bite humans, cattle, horses, dogs, and many other mammals. Female deer flies feed on blood, while male deer flies feed on pollen. When a female deer fly bites you, it is likely to be painful (some describe it as similar to a bee sting), and the fly’s saliva may cause the bite to itch and hurt. Some people might have extreme allergic reactions to the bite.

By the time they’re fully grown, deer flies are very large compared to the average housefly — the typical deer fly size is anywhere from 0.25 to 1.25 inches long. Deer flies are distinct from horseflies in a few ways; the easiest deer fly identification is their huge eyes and the purple or green bands found on their blue or yellow-green wings. Their mouths are noticeable because they extend downward and jut out ahead of the rest of the head. Deer fly wings are big and shaped like fans to help them cross long distances quickly. 

These flies are found in wooded, wetland, and damp ecosystems because during the early stages of the deer fly lifespan, the larvae need an aquatic environment. They pupate and eat tiny insects that they find around muddy edges of the water. Birds, dragonflies, hornets, wasps, spiders, toads, and frogs are all natural predators of deer flies.

Deer and horseflies come from the Tabanidae family, also known as tabanids or tabanid flies. Globally, there are more than 4,000 species of deer flies and horseflies, with around 335 in the United States. More than 110 of these are deer fly species, and more than 160 are horsefly species. Indiana is home to the majority of these species.

Eggs. Deer flies lay eggs in large quantities, ranging from 100 to 1,000 at a time. The eggs are layered on vertical surfaces like aquatic vegetation, sticks, foliage, and rocks directly above water or damp ground to support the larvae portion of the life cycle.  Usually, the eggs are covered with a chalk-like or shiny substance that helps protect them from getting wet. Once laid, eggs have a creamy white appearance that turns dark gray or black as the eggs mature. Eggs have a cylinder-like shape and are very small, ranging from 1 to 2.5 millimeters long. After about a week, the eggs hatch, and the new larvae drop to the wet or damp ground below.

Larvae. During this stage of the deer fly life cycle, the larvae might be fully aquatic, semi-aquatic, or completely terrestrial. Larvae are long with tapered ends and are white, brown, or green depending on their species. Usually, they’ll have dark bands at each section of the body. This stage can take a few months or a full year.

Pupae. During the pupal stage, pupae are brown and rounder than larvae, with wings and legs that start to develop. This stage lasts for a few weeks.

Adults. After coming out of the pupal case, deer flies mate. Males go after the females in the air, begin to mate in the air, and then complete mating on the ground. A female will then drop her group of eggs and move on to find a host.

Female deer fly bites are especially painful due to how the mouth works. Each mouth contains two pairs of blade-like appendages that cut into the skin to start blood flow, and then the fly soaks the blood up with its spongy mouth area. Male deer fly bites are not as painful because their mouths, although constructed similarly, are a lot weaker than female mouths.

Although similar biting insects transmit disease with their bites, deer fly bites are not typically known to pass on dangerous conditions, although plenty of bacteria, viruses, and protozoa live on the females’ mouths and in their digestive systems. The only exception has been found in the western part of the United States, where a type of deer fly transmits tularemia, also known as deer fly fever or rabbit fever. Ticks and small game animals that are already infected are a much bigger issue when it comes to tularemia.

Deer fly bite treatment is simple:

  • Remove yourself from the area where you were bitten.
  • Wash the affected area gently with soapy water.
  • Cover with a cold washcloth to help with swelling or pain.
  • Elevate the area if it’s on one of your arms or legs.
  • Apply baking soda paste, calamine lotion, or hydrocortisone cream.
  • Take an oral anti-itch medicine or pain reliever if necessary.

Any stinging, swelling, or itching should go away after a few days. If your symptoms get worse or don’t improve; you have signs of infection; or you develop any concerning side effects like nausea, hives, or trouble breathing, reach out to your healthcare provider immediately. You may need emergency care.

Are you wondering how to get rid of deer flies? At the moment, there are no effective methods for managing large populations, although traps can help in small spaces like yards, swimming pools, and campsites. Generally speaking, however, it’s nearly impossible to get rid of deer flies or protect yourself from them. Insecticides aren’t powerful enough, and trapping devices have limited effects. Insect repellents won’t protect your body well; your best bet is to wear thick, long sleeves and pants and a hat with good coverage if you are going to spend time in locations infested with deer flies.