Deer Fly: All You Need to Know for a Bite-Free Summer

Deer flies are small to medium-sized insects, typically ranging in length from 7 to 10 mm. These pests are known for their persistent and painful bites, which can cause discomfort to both humans and livestock. They vary in color from yellow to black, often have stripes on their abdomen, and display distinct mottled wings with dark patches.

These flies belong to the same family as horse flies, but are usually smaller in size. One interesting feature of deer flies is their large compound eyes, which are often marked with florescent green lines or dark purple to black hues.

Deer flies are generally found around wet and wooded areas, and their bites can transmit a variety of diseases to humans and animals. In the following sections, we’ll uncover more about their biology, life cycle, and how to effectively control their population and protect ourselves from their painful bites.

What Is a Deer Fly?

A deer fly is a small to medium-sized insect belonging to the Tabanidae family. They are typically 10-13 mm long and are known for their persistent biting behavior, affecting humans and livestock alike.

Deer flies have distinct features that set them apart from other insects:

  • Yellow to brown in color
  • Patterned wings
  • Thorax is greenish-yellow with dark stripes

Deer flies are often compared to their larger counterparts, horse flies. Here’s a comparison table highlighting their differences:

Feature Deer Fly Horse Fly
Size Small to medium (10 to 13 mm long) Moderate to large (14 to 19 mm long)
Color Yellow to brown Grayish-brown
Wings Tinted smokey gray-brown or dark patterns Clear
Thorax Greenish-yellow with dark stripes Grayish-brown

Deer flies are found in several species, with Chrysops as their genus. They are economically significant in regions like Florida, where they are considered fierce biters. Like mosquitoes, female deer flies are responsible for inflicting bites.

In summary, a deer fly is a small to medium-sized, biting insect that belongs to the Tabanidae family. Their distinct features and penchant for biting set them apart from other insects, making them a notable concern for both humans and livestock.

Physical Characteristics

Size and Color

Deer flies are relatively small insects, usually ranging in length from 7 to 10 mm1. They exhibit a variety of colors, often appearing yellow to black, with stripes on their abdomen1.

Wings

The wings of deer flies are quite distinctive, with a tinted, smokey gray-brown color, or sometimes displaying dark patterns2. This is in contrast to horse flies, which typically have clear wings2.

Eyes

Deer flies have large, striking eyes often marked with vibrant colors. They can be dark purple or feature florescent green bands, creating a stunning visual effect1.

Antennae

The antennae of deer flies, while not as prominent as other features, are an essential part of their anatomy, aiding in navigation and sensing their environment.

Comparison Table

Feature Deer Flies Horse Flies
Size 7 to 10 mm 10 to 25 mm
Wing Color Smokey gray-brown, dark patterns Clear
Eye Color Dark purple, green bands Bright colors3
Body Color Yellow to black, stripes Grayish-brown2

Life Cycle of Deer Flies

Eggs

Deer flies typically lay their eggs in wet or marshy habitats, often near a water source. The female deer fly will deposit a mass of about 100 to 800 eggs, usually on vegetation overhanging water or moist soil. These eggs are:

  • Tiny
  • Dark in color
  • Cylindrical in shape

Larvae

Once the eggs hatch, the larvae drop into the water or damp soil where they start their development process. Deer fly larvae are:

  • Legless
  • Cylindrical-shaped
  • Equipped with small, sickle-shaped mouthparts capable of slicing through prey

During their larval stage, deer flies feed mostly on small insects, crustaceans, and other organic matter. They molt several times during the development process and pass through multiple stages called instars.

Pupae

After the final molt, deer fly larvae enter the non-feeding pupal stage. Pupae are:

  • Encased in a dark-colored exoskeleton
  • Found in moist soil, often under debris

This pupal stage lasts for about a week or two, during which the insect transforms into its adult form.

Adults

Adult deer flies emerge from the pupal stage, ready to seek out a meal. Key aspects of adult deer flies include:

  • Males mainly feed on pollen and nectar
  • Females require a blood meal to facilitate egg development

Both male and female deer flies have distinct features:

  • Large, patterned eyes (gold or green)
  • Dark bands across their wings

Comparison Table: Deer Fly Life Stages

Life Stage Key Features
Eggs Tiny, dark, cylindrical
Larvae Legless, cylindrical, mouthparts for slicing
Pupae Non-feeding stage, dark exoskeleton
Adults Males feed on nectar, females bite for blood

By understanding the life cycle of deer flies and their habitat preferences, you can better protect yourself and your animals from these pesky insects.

Deer Fly Behavior

Activity Patterns

Deer flies are most active during the day, particularly in warmer months. Some factors affecting their activity include:

  • Temperature: Deer flies prefer temperatures above 60°F (15°C)
  • Weather: They are less active on windy or cloudy days

Feeding Habits

Deer flies feed on a variety of sources, with distinct dietary preferences for males and females:

  • Male deer flies primarily feed on nectar and pollen from flowers
  • Female deer flies require blood meals for reproduction and will bite humans and animals, such as cattle or deer, to obtain nutrients

Female deer flies locate their prey using carbon dioxide cues and attack their victims during the day. Here are some noteworthy feeding behaviors:

  • They typically bite the head, neck, or shoulders of their prey
  • They use their scissor-like mouthparts to make a small incision and then sponge up the blood

Deer flies can be a nuisance for humans, but they also play a role in the ecosystem by being part of the food chain for natural predators like birds, frogs, and spiders.

Reproduction

Deer fly reproduction is closely linked to their feeding habits, as the blood meal provides necessary nutrients for egg development. The female deer fly lays her eggs in clusters on damp soil or vegetation near water sources. These eggs hatch within about one week, and the emerging larvae will feed on organic matter in their surroundings before pupating and eventually emerging as adult deer flies.

Deer Fly Bites

Painful Bites

Deer fly bites can be very painful due to their mouthparts that cut into the skin to access blood. The intense pain might only last for a short time, but discomfort can persist.

Allergic Reactions

Some individuals may experience allergic reactions to the salivary secretions released by deer flies as they feed. Common symptoms include:

  • Swelling
  • Weakness
  • Rarely, severe allergic reactions

Diseases and Infections

Deer flies are not known to transmit eastern equine encephalitis (EEE) or West Nile virus (WNV). However, they can transmit tularemia, also known as “deer fly fever” or “rabbit fever.” Symptoms of tularemia may include:

  • Fever
  • Weakness
  • Bacterial infection
Disease or Infection Transmission by Deer Flies
Eastern Equine Encephalitis (EEE) No
West Nile Virus (WNV) No
Tularemia (Deer Fly Fever/Rabbit Fever) Yes

While deer fly bites can be painful and result in allergic reactions or infections like tularemia, they are not known to transmit EEE or WNV.

Identification and Prevention

Distinguishing Deer Flies from Other Insects

Deer flies are small to medium-sized flies (10 to 13 mm long) with wings that are tinted smoky gray-brown or have dark patterns1. They have a greenish-yellow thorax with dark stripes1. Their appearance is distinct from horse flies, which are larger (14 to 19 mm long), have clear wings, and a grayish-brown thorax1.

Characteristics of Deer Flies:

  • 10 to 13 mm long
  • Smoky gray-brown or dark-patterned wings
  • Greenish-yellow thorax with dark stripes

Characteristics of Horse Flies:

  • 14 to 19 mm long
  • Clear wings
  • Grayish-brown thorax

Natural Predators

Deer flies have natural predators such as birds, dragonflies, and certain species of wasps and hornets2. These predators help in controlling deer fly populations.

Trapping Devices

Traps can be effective in controlling deer flies. One example is the Trolling Deer Fly Trap, which can be attached to a hat or cap to catch deer flies that swarm around the head.

Pros of trapping devices:

  • Non-toxic
  • Reusable
  • Can reduce deer fly populations

Cons of trapping devices:

  • May need to be replaced or cleaned periodically
  • May not be 100% effective

Repellents and Control

Using insect repellents containing DEET or picaridin can help repel deer flies and protect against bites3. Personal protection measures such as wearing long sleeves, pants, and hats can also minimize exposure to deer flies.

Comparison of DEET and Picaridin:

Feature DEET Picaridin
Effective Yes Yes
Long-lasting Moderate Long-lasting
Odor Strong Mild
Safe for gear Can damage gear Gear-safe

Habitat and Distribution

Deer flies belong to the genera Chrysops and Tabanus. They are common in rural areas such as fields, pastures, grasses, and shrubbery. Indiana is one of the many states where deer flies can be found.

These insects usually reside in bird habitats or lay their eggs in damp soil, close to water sources. While deer flies prefer places with abundant vegetation, horse flies, another related species, can also be found in similar habitats.

The following are some features and characteristics of deer flies:

  • Size: 10 to 13 mm long
  • Wings: Tinted smokey gray-brown or with dark patterns
  • Thorax: Greenish-yellow with dark stripes

In comparison, horse flies are larger, with a size of 14 to 19 mm long, clear wings, and a grayish-brown thorax.

Here’s a comparison table between deer flies and horse flies:

Deer Flies Horse Flies
Size 10 to 13 mm long 14 to 19 mm long
Wings Tinted smokey gray-brown Clear
Thorax Greenish-yellow Grayish-brown

In summary, deer flies and horse flies share similar habitats, but they differ in size and physical appearance. Deer flies are more commonly found in bird habitats, while horse flies can also thrive in such surroundings. Both species are attracted to rural areas with fields, grasses, and shrubbery, where they can find ample food sources and suitable environments for laying eggs.

Deer Flies and Human Interaction

Deer flies are a type of biting insect known to be a nuisance to humans, wildlife, and livestock. They belong to the genus Chrysops and are smaller in size compared to horse flies, usually having dark bands across their wings1.

Their bites can be painful and annoying, often causing red, itchy welts on the skin. Female deer flies need blood meal to produce eggs, and that’s when they bite humans and animals2.

Outdoor activities during warm months are at higher risk of encountering deer flies. They are attracted to movement and can be especially bothersome while hiking, camping, or performing outdoor work3.

Prevention and protection from deer fly bites:

  • Wear light-colored clothing, as they tend to be attracted to dark colors
  • Apply insect repellent containing DEET to exposed skin
  • Wear long-sleeved shirts and long pants to reduce exposed skin
  • Use wide-brimmed hats with attached nets to protect the head and neck area

Despite being a nuisance, deer flies don’t typically transmit diseases to humans4. Keeping their bites in mind, taking preventive measures can help minimize discomfort and ensure enjoyable outdoor experiences.

Additional Facts and Information

Deer flies are small to medium-sized insects belonging to the Tabanidae family. They measure about 10 to 13 mm long with wings tinted smokey gray-brown or dark patterns. Some notable characteristics of deer flies include:

  • Greenish-yellow thorax with dark stripes
  • Aggressive nature towards humans and animals
  • Possess large eyes and sharp mandibles for biting

Female deer flies are especially attracted to mammals, including humans, due to their higher carbon dioxide output. Deer flies are considered a nuisance to humans and small game animals because of their painful bites.

These insects have a relatively short lifespan, typically ranging from 30 to 60 days. Although not considered highly dangerous, their bites can cause allergic reactions in some individuals.

When dealing with deer flies, insecticides can be effective in controlling their population. However, it is essential to use these chemicals cautiously to prevent harm to other non-target organisms.

In comparison to other insects, like mosquitoes, deer flies are relatively larger and more aggressive biters. A comparison of deer flies and mosquitoes can be seen in the table below:

Feature Deer Fly Mosquito
Size 10 to 13 mm long 3 to 6 mm long
Bite Painful, aggressive Less painful, less aggressive
Attraction Carbon dioxide output Carbon dioxide, body heat, odors

In conclusion, deer flies are an interesting yet troublesome insect species. Their aggressive nature and painful bites can make them unwelcome visitors during outdoor activities. Being aware of their characteristics and potential dangers can help you better deal with them and manage their presence.

Footnotes

  1. https://entnemdept.ufl.edu/creatures/livestock/deer_fly.htm 2 3 4 5 6 7

  2. https://content.ces.ncsu.edu/horse-flies-and-deer-flies 2 3 4 5

  3. https://entomology.ca.uky.edu/ef511 2 3

  4. https://extension.entm.purdue.edu/publichealth/insects/tabanid.html

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Deer Fly

 

Swirly-eyed fly
Location: Black Mountain, North Carolina
July 4, 2011 7:43 pm
I was wondering if you could identify this fly for me – I haven’t been able to figure it out. It was a little smaller than a regular house fly. Found it sitting calmly on my car windshield a few days ago.
Thanks!
Signature: Dakota

Deer Fly

Dear Dakota,
We believe we have identified your Deer Fly as
Chrysops fulvistigma, by matching the photos on BugGuide.  The genus page on BugGuide gives detailed instructions for taking photos of four different views of specimens whenever possible to assist in proper identification.  It is possible we have the species wrong, but we are relatively confident with the genus.

Letter 2 – Deer Fly

 

Subject: Evil Beach Fly in; War against the Photographers
Location: Oregon, OH (near Toledo)
July 10, 2012 8:11 am
G’day Bugman.
I went to the beach today. Not your normal fun-in-the-sun beach. This was the stunning Magee Marsh nature preserve. I took my doggy companion, and we had planned on a nice two hour walk around the beach and the trails to photograph bugs.
Well, after finding that the board walk is off limits to pets (Understandable with all the bird photographers,) and the other path is off limits due to Bald Eagle nesting, we wanted to stick to the beach. However, while I did find plenty of bugs… They were all the same bug. And they were on a mission. Thousands of these bugs were hovering above the sand, and I was hoping they would mind their own business. However, upon my entering the beach, they began relentlassly harassing my dog and I. They’d get in my dogs ears, and were obsessed with trying to get in my face, on my neck, and on my hand. I ran back to my car, and applied my emergency bug spray (deet based) and my dog’s bug spray (not deet based,) which I hate to use but I really wanted to get some photos in and I’m a bit of a pansy. They were completely undeturred.
I’m bad at flies… It looks like maybe a deer fly to me, but since there are very few deer around (rabbits are about the only mammal that hangs out there in any mass) it seemed odd. Any ideas? Were they being territorial/defensive, or did I just look tasty? I did not actually get bit that I am aware of, so I can’t say if they’re a biting fly.
… And I didn’t actually think they were evil. But I do wish I could have explained to them what a long drive I took to get there and how much I’d enjoy if they’d give me some peace 🙂
Signature: Katy

Deer Fly

Hi Katy,
We are sorry to hear your Oregon beach experience was unpleasant.  We agree that this is a Deer Fly, and it very closely resembles
Silvius gigantulus which is pictured on BugGuide.  Additionally, BugGuide has received reports from California and Washington in June and July, so it can be deduced that the species also ranges in Oregon and would appear at the same time of year.  OOPS, we just realized you are in Ohio and the city is Oregon, but the fly still looks correct.  We will see if the genus is represented in Ohio.

Letter 3 – Deer Fly

 

Subject: What’s this biting fly?
Location: Orlando
March 18, 2016 9:37 am
Can you identify this biting fly? It has a slightly painful bite. It’s similar to a deer fly but black-bodied instead of yellow. Orange spot on head. Orlando in March. Lots of them bothering us.
Signature: Anemic in FL

Deer Fly
Deer Fly

Dear Anemic in FL,
We believe we have correctly identified your biter from Florida as a Deer Fly,
Chrysops divisus, based on this BugGuide image, also from Florida and also credited with biting.  According to BugGuide:  “Known only from Florida and Georgia. B & H show distribution in extreme SE Georgia (4 counties)” and “in Florida flies from late February to late July in Georgia April – June.”  BugGuide also notes:  “Regarded as a serious pest of man in Florida.”

Letter 4 – Deer Fly

 

Subject: mosquito or fly
Location: shamong nj
July 10, 2017 9:42 am
was bitten by this bug several times – came home and about 12 hours later a welt appeared and itching badly. Woke me up from a dead sleep at 4am . what is it?
Signature: itchy

Deer Fly

Dear itchy,
This is a Deer Fly, and females are blood-sucking biters.

Thank you.  I felt the bites but a few family members did not but we all woke up with itchy feet in the middle of the night – so it started a debate as to what it was, I managed to kill one the next day and take a picture of it so we will know  how to treat the bites so it was effecting the family dogs also.

 

Letter 5 – Deer Fly

 

Subject:  horsefly?
Geographic location of the bug:  Florida
Date: 07/05/2018
Time: 09:13 PM EDT
Your letter to the bugman:  Is this a horsefly?
How you want your letter signed:  uh

Deer Fly

Dear uh,
This is a Deer Fly, not a Horse Fly, but they are in the same family Tabanidae, so they share many similarities.  We believe your individual is in the genus
Chrysops, and according to BugGuide:  “100 spp. in 2 subgenera in our area.” Alas, we haven’t the necessary skills to provide a conclusive species identification.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

Leave a Comment