Deer flies and horse flies belong to the Tabanidae family and are both known for their annoying and painful bites. These bloodsucking insects can be quite bothersome, especially to cattle, horses, and humans. Understanding the differences between them can help you better identify and manage these pests.
Deer flies are typically smaller, measuring between 10 to 13 mm long, with greenish-yellow thoraxes featuring dark stripes. Their wings appear tinted smokey gray-brown or showcase dark patterns. On the other hand, horse flies are larger, ranging from 14 to 19 mm in length, and possess clear wings and grayish-brown thoraxes.
Aside from their physical distinctions, each species’ behavior and habitat can also vary.
Deer Fly and Horse Fly: A Comparison
Appearance
Deer flies and horse flies are bloodsucking insects with a few differences in appearance. Let’s examine their distinct characteristics:
- Deer flies:
- Horse flies:
Habitat
Both deer flies and horse flies can be found in environments with nearby water sources due to their aquatic larval stages3. However, deer flies are more often encountered in wooded areas, while horse flies prefer open areas such as pastures and meadows4.
Distribution
Deer flies (Chrysops) and horse flies (Tabanus) can be found across most regions of the United States, although they’re more prevalent in warmer climates5. Notable differences in distribution include:
- Deer flies: Higher concentrations in the southeastern US5
- Horse flies: Widespread throughout the US but less common in arid regions5
Comparison Table
| Feature | Deer Fly | Horse Fly |
|---|---|---|
| Size | 6-10 mm | 20-25 mm |
| Wing Appearance | Dark bands | Clear or solid |
| Eye Color | Brightly colored | Vibrant |
| Preferred Habitat | Wooded areas | Open areas |
| Distribution | Southeastern US | Widespread in US |
Life Cycle and Reproduction
Eggs
- Both deer flies and horse flies lay their eggs on vegetation near wetlands or aquatic habitats.
- Females typically lay eggs in specific locations, for example on vegetation overhanging water3.
Larvae
- The larvae of both flies are generally white, brownish, or greenish in color1.
- Deer fly larvae are usually smaller than horse fly larvae1.
- Both types of larvae are spindle-shaped and taper to a point at both ends1.
- Larval stage feeding habits:
Pupa
- Winter is spent in the larval stage, with pupation occurring in spring3.
- The pupal stage of both flies is spent in the same aquatic or wetland habitat as the larvae3.
Adult
- Adult emergence happens during late spring and summer3.
- Deer fly adults are 6-10 mm long and yellow to brown in color with patterned wings5.
- Horse flies range in size from 3/4 to 1-1/4 inches long, with clear or solidly colored wings and brightly colored eyes2.
Comparison Table:
| Aspect | Deer Fly | Horse Fly |
|---|---|---|
| Size | 6-10 mm long5 | 3/4 to 1-1/4 inches long2 |
| Wing Patterns | Patterned5 | Clear or solidly colored2 |
| Larval Habitat | Wet or semi-aquatic environments4 | Wet areas or terrestrial environments5 |
| Adult Habitat | Wetlands, aquatic1 | Wetlands, aquatic1 |
Feeding and Biting Habits
Adult Feeding Habits
Both horse flies and deer flies exhibit different feeding habits among their male and female counterparts. As adults, male horse flies and deer flies primarily feed on nectar, while their female counterparts need blood meals for egg production.
Female horse flies and deer flies are attracted to several factors from potential hosts, including carbon dioxide, body heat, and movement. For example, female deer flies tend to bite humans while they are outdoors near wooded areas.
Blood-Sucking Bites
The bites from both horse flies and deer flies can be quite painful, as their mouthparts cut the skin rather than pierce it. This blood-sucking habit can lead to the spread of various diseases and infections.
The bite differences can be seen below:
| Feature | Horse Fly Bite | Deer Fly Bite |
|---|---|---|
| Pain Level | More painful | Less painful |
| Bite location | Exposed skin | Exposed skin |
| Mouthparts | Scissor-like | Scissor-like |
Horse Flies
- Larger size (14 to 19 mm long)
- Clear wings
- Grayish-brown thorax
- More aggressive bites
- Found near livestock, such as in barns
Deer Flies
- Smaller size (10 to 13 mm long)
- Tinted or patterned wings
- Greenish-yellow thorax with dark stripes
- Less aggressive bites
- Found in wooded and marshy areas
Some ways to protect yourself and animals from these bites include using essential oils, wearing protective clothing, and avoiding areas where these flies are more prevalent. Horse and deer flies are daytime biters, so turning horses out at night instead of the day can help reduce biting. Providing shelter or canopy trees far from wooded edges can also protect horses from bites.
Health Impacts and Control Methods
Diseases Transmitted
Deer flies and horse flies are blood-sucking insects that can be serious pests for livestock and humans. They can transmit various diseases in the process, some of which include:
- Anaplasmosis: A bacterial infection that affects mostly cattle, but can also impact sheep and goats.
- Tularemia: A bacterial disease affecting humans, known as “rabbit fever.”
- Equine infectious anemia: A viral disease that affects horses.
- Hog cholera: A highly contagious viral disease in pigs.
- Anthrax: A bacterial infection that can infect livestock and humans.
- Filariasis: A parasitic infection transmitted by deer flies that can cause health problems in humans.
Prevention and Repellents
Preventing deer fly and horse fly bites is essential in controlling the spread of diseases. Some effective measures include:
- Regularly inspect and maintain fences and screens to minimize access for flies.
- Use approved pesticides, like permethrin-based sprays, to control flies in livestock areas.
- Apply repellents to livestock and humans when in infested areas.Examples of deer fly and horse fly repellents:
- DEET-based repellents
- Picaridin-based repellents
- Natural oil-based repellents (e.g. eucalyptus or lemon oil)
Comparison Table
| Feature | Deer Fly | Horse Fly |
|---|---|---|
| Size | 6-10 mm long | 14-19 mm long |
| Color | Yellow to brown | Grayish-brown |
| Wings | Patterned | Clear |
As members of the family Tabanidae, deer flies and horse flies share some common characteristics. Tabanid flies are robust, capable of biting, and can transmit diseases to both livestock and humans. The health impacts of these pests can be severe if not controlled properly through prevention and the use of repellents.
Interesting Facts and Behaviors
Predators and Prey
Deer flies and horse flies are known as bloodsucking pests that can cause discomfort to humans and animals. They can be active in various environments, such as forests and wetland environments. Adult female deer flies and horse flies feed on the blood of mammals, while adult males feed mainly on pollen and nectar.
Some common predators of these flies include birds and other insects. Interestingly, some people utilize fly traps outdoors to control their numbers around their property.
Mating and Attraction
The mating habits of deer flies and horse flies are quite fascinating. Males and females come together in a specific location, usually near vegetation, to mate.
| Deer Flies | Horse Flies |
|---|---|
| Smaller in size (10 to 13 mm long) | Larger in size (14 to 19 mm long) |
| Greenish-yellow thorax | Grayish-brown thorax |
| Smokey gray-brown wings | Clear wings |
In order to attract mates, male flies often rely on visual cues. Once the female is attracted, the pair will engage in a flight dance before mating. After mating, female flies will search for a suitable host to feed on in order to obtain the nutrients necessary for egg development.
- Both flies undergo metamorphosis, passing through egg, larva, pupa, and adult stages.
- Can be found in outdoor and wetland environments.
While there are many similarities between deer flies and horse flies, they do have some different features that set them apart. By observing their distinct sizes, thorax colors, and wing patterns, it’s easier to identify which is which.
It’s important to protect yourself and your animals from these bloodsucking pests by using protective clothing, repellents, and fly traps when necessary.
Footnotes
4 Comments. Leave new
My instinct told me it was a horsefly… but I didn’t know what to think, as all previous horseflies I’d ever seen were the black horseflies.
Thanks for the identification!
I’ve more often found these flies inside parked cars at the end of a hike.
Given that these flies are likely to have evolved the ability to seek out targets that radiate body-warmth, it’s possible that 1, flies pursuing human targets end up in the cars because of that, or 2, the actual heat of the car is a trigger for them, and in circling their potential meal-item they fly through a half-open window and become trapped.
hi I was at the beach and a min later I saw lot of flies and when they got closer I started to get scared and then they started to bit I don’t know what
it was I think it was a female horse flies but they looked super mad I don’t know what it is and I fear it poisons or something worse because I don’t want my family and dog in danger please help me
I call those B52’s. I swear they take a literal chunk of skin out when they bite! I love bugs but freely admit to carnage when it comes to these mo-fo’s. 😀