Black Fly Bites on Dogs: Symptoms, Treatment, and Prevention

If you’ve been out for a walk near water, hit the trails, or just let your dog roam the backyard, and now they’re covered in itchy red marks, black flies might be the culprits. This guide breaks down everything you need to know—how to spot black fly bites, treat them, and most importantly, how to prevent black fly bites on dogs. Your dog’s comfort is worth it. Let’s get into it! 

What Are Black Fly Bites on Dogs?

Black flies—also known as buffalo gnats because of their arched backs—are tiny (2–5 mm) but aggressive insects. Unlike mosquitoes that gently pierce the skin, black flies actually slice it open to feed on blood. Sounds awful, right? That’s why their bites often hurt more and look worse.

They’re most active during the day in late spring and early summer, especially in moist environments like wooded trails, lakes, and streams—aka your dog’s favorite places.

Dogs, especially those with short or thin coats, are easy targets. Common bite areas include:

• Ears
• Belly
• Groin
• Around the eyes

If your dog comes back from an outing and starts scratching like mad, black flies might be to blame.

Where Do Black Flies Bite Dogs?

Without a thick coat of fur, dogs are prime targets. Black flies frequently target the belly, muzzle, inner thighs, ears, crotch, and area surrounding the eyes. That’s why many pet owners first notice black fly bites on a dog’s belly—a common hot spot due to the lack of fur and accessibility. You might not spot the bite right away, but trust that you’ll notice the aftereffects. Bottom line? Dogs provide them with the blood they need to survive. (Of course, black flies bite other animals, too!).

Why Are Their Bites Problematic?

Although black fly bites are not usually dangerous on their own, they can become problematic if:

• The dog has a sensitivity or allergy to insect bites. 
• The dog scratches or licks the affected area excessively, leading to open wounds or infections.
• The bites are mistaken for other conditions, such as ringworm or tick bites, leading to delayed or incorrect treatment.

Because they slice the skin rather than pierce it, a black fly bite can cause more than just a little itch. Expect inflammation, relentless scratching, or even, in some cases, nasty infections.

Symptoms of Black Fly Bites

Common Signs

Most black fly bites on dogs appear as small, red, circular marks. One distinguishing feature is the “bullseye” or target-like appearance—a red ring with a paler center, similar to ringworm. However, black fly bites vs. ringworm on dogs have a few key differences:

• Black fly bites are often raised, irritated, and scabby.
  Ringworm is typically flat and scaly and may spread gradually over days or weeks.

Look for:

• Red bumps or circular rashes, often on the belly or groin.
• Scabbing or crusting over the site.
• Persistent scratching or licking of the area.
• Hair loss around the bite site.

Severe Reactions

More severe symptoms, such as

• Swelling around the face or neck can occasionally occur in dogs.
• Lethargy or vomiting could be signs of an allergic reaction.
• Discharge or pus from the bite, which could indicate an infection.
• Hot areas or more extensive skin irritation regions.

If these symptoms appear, veterinary care is necessary immediately.

Treatment Options

At-Home Care

If the bites are mild and your dog is otherwise healthy, you can manage the condition at home.

1. Cold Compress

Apply a cold, damp cloth or wrapped ice pack to reduce inflammation and soothe itching. Use for 5–10 minutes, 2–3 times a day.

2. Topical Creams

Use pet-safe anti-itch creams or sprays containing hydrocortisone or aloe vera (never use human creams unless advised by a vet).

3. Prevent Scratching

The hard part, right? But stopping your dog from scratching is key to preventing infection. An Elizabethan collar (the cone of shame) might be needed. Sometimes a bandage can help protect the area and minimize scratching, so that can be applied and help it stay on the bite area.

Veterinary Care

If your dog’s symptoms worsen, or you’re not sure if it’s a black fly bite or something else like ringworm or ticks, visit your vet clinic.

1. Antihistamines

Vets may recommend antihistamines like Benadryl (diphenhydramine), based on your dog’s weight and condition.

2. Antibiotics

Infected bites need antibiotics to fight the bacteria. Your veterinarian will determine the appropriate course of treatment based on the type of bacteria causing the infection and the antibiotic that is chosen. Make sure your dog finishes the whole course, even if they seem better, to prevent antibiotic resistance.

3. Allergy Management

For serious allergic reactions with trouble breathing, a rapid heart rate and more. Your vet might give corticosteroids or other allergy meds to reduce inflammation. These medications assist the reaction to subside by suppressing the immune system.

4. Pain Relief

Pain relief medication can only be prescribed by a vet if it’s the right route for your pet.

When to seek immediate help? If you see an infected area (pus, excessive redness, stinkiness) and allergic symptoms (breathing problems, facial swelling, collapse), head to the vet, fast.

Prevention Tips

The best way to handle black fly bites on dogs is to avoid them altogether.

1. Avoid High-Risk Areas and Times

Black flies thrive in areas near standing water. Avoid these places during peak hours, typically dawn and dusk. Plan walks or outdoor time when it’s sunny and breezy, as flies are less active in those conditions.

2. Protective Clothing

Clothing can help cover spots where they are getting bit, covering most of the dog’s body to prevent bites.

3. Vet-Approved Repellents

Look for products that specifically state “safe for dogs” and are made with natural oils like cedarwood, lemongrass, or citronella.

Important: Never use DEET

DEET-based repellents (used by humans) are toxic to pets and should never be applied to dogs, even in small amounts.

4. Grooming and Inspection

• Keep your dog well-groomed to make it easier to spot bites.
• After walks, inspect your dog’s belly and legs for any red marks.
• Regularly wash your dog’s bedding and gear, especially during fly season.

Final Tips

• Recognize: Red, circular bites with possible scabs, especially on the belly.
• Treat: Use cold compresses and safe creams, and visit your vet if symptoms worsen.
• Prevent: Avoid fly-prone areas, cover vulnerable skin, and use pet-safe repellents.

Spot the signs, treat the bites, and take steps to prevent them. This helps give your dog a happy and safe bug-free life. If you need more help, reach out to your local vet.