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black fly bites

© Ann Arbor Animal Hospital

 The essentials

  • Black or horsefly bites are mostly harmless — The stings from these pesky insects aren’t as bad as they look, but can still be itchy.
  • Allergic reactions are rare but can be serious — Hives or swelling in areas other than the bite are signs of anaphylaxis. If you notice this, call your vet immediately.
  • Summer isn’t the only risky season — Bug bites and stings can happen at any time of year, so year-round prevention is important.

Black flies — also referred to as gnats or buffalo gnats – are known to swarm in large groups. That sounds bad, but unlike diseases that may come along with tick and mosquito bites, black fly bites are mostly harmless and often heal without medical attention, sometimes in a matter of days, even though they look scary.

Even with regular use of flea and tick medication, your dog can still get bitten — but the good news is that these bites are typically no cause for concern.

What do black fly bites look like on dogs?

Bites usually appear on dogs as flat, red splotches that may or may not be outlined. It’s often called a “bullseye” due to the outline, but the entire splotch may sometimes be a completely dark red lump. Black flies tend to bite exposed areas of your pup’s skin like their belly, inner thighs, or ears.

Different types of fly bites

Small flies, like yellow flies and no-see-ums, leave a smaller mark. Larger flies, like black and horse flies, primarily buzz around large farm animals and can sometimes draw blood. Adults are small (~1/16 inch), have a stout, dark-colored, rounded back, broad wings, and short legs with a few hairs on their bodies.

👉 See our helpful bug bite guide for tips on the treatment of different bug bites on dogs. 

Where are black flies typically found?

Black flies live around flowing water like streams and rivers. Here they lay eggs and the larvae attach to rocks before emerging as flying adults.

They’re also commonly found on and near farms or in wooded areas and lowlands. If your dog has been near any of these environments, the greater the likelihood that the bite that you’re looking at came from a black fly.

They tend to be most active in humid, wooded regions during the warmer months but can be found year-round in semi-tropical regions.

When to call your vet

If the bites don’t improve or look worse in a few days or your dog won’t stop itching them, call your vet for treatment advice.

Additionally, there are four types of common allergic reactions that your dog could have after an insect bite or sting. However, only two are considered life-threatening.

  • Hives (urticaria). These are annoying and itchy, but they’re not life-threatening.
  • Allergic dermatitis. Your dog will have itchy, and sometimes flaky skin.
  • Edema. You’ll notice significant swelling in the face or throat. If edema is caused by an allergic reaction, it can be treated with an antihistamine injection. It’s fatal when the swelling impairs your pup’s ability to breathe.
  • Anaphylaxis . This severe allergic reaction can be fatal without treatment. Symptoms can reach a life-threatening stage in as little as 20 minutes.

🚨If your dog presents with vomiting, diarrhea, seizures, weakness, difficulty breathing, excessive drooling, pale gums, or hives and swelling in areas other than where the bite mark is, consult a vet right away as these can be signs of anaphylaxis and other larger issues that need to be addressed.

How to soothe and treat fly bites on your dog’s skin at home

Even if a fly bite isn’t life-threatening, it can still bother your dog and affect their quality of life. Scratching and licking irritated, itchy skin will only add to the misery.  Here’s the best way to treat these painful bites:

First, you’ll want to start by carefully cleaning the affected area with warm, soapy water. Be gentle, as this area may be sensitive for your dog. If the wound has scabbed over, you may need to lightly press a warm compress on the scab to soften it before cleaning. Then, apply an ointment or even a paw balm on the wound for healing. Keep your dog indoors for a bit to ensure it doesn’t get dirty or the ointment doesn’t rub off.

  • Oatmeal baths — Oatmeal has anti-inflammatory properties and can soothe your dog’s angry skin.
  • Ice the bite with a cold pack — Ice will help to reduce pain and swelling and is a great first step in combating itching.
  • Hydrocortisone — When applied in small amounts where your dog can’t lick, this cream can treat the inflammation and itchiness your pup is experiencing.
  • Epsom salt — A quick and easy remedy for simple wounds and swelling, Epsom salt baths can provide relaxing relief to your pet.
  • Applying a baking soda paste — A 1:1 combination of baking soda and water can form a paste that helps reduce redness and inflammation on the bite areas.

If you notice that the bites aren’t getting better or that the affected area is worsening, consult your vet since it could be a sign of a bacterial infection or other skin issue.

As with any non-food item, please ensure your pet doesn’t ingest any of these treatments through licking or drinking.

🚨 Avoid using calamine lotion on your dog, as too much zinc is toxic to dogs .

Preventing fly bites on dogs

Since flies are widespread geographically and very active during certain times of the year in some places, it’s not always possible to avoid them. Here are some tricks to keep their bite count to a minimum.

Keep your dog’s coat and skin clean — It’s good for general health maintenance, too.

Clean pet waste in your yard — This includes any uneaten food scraps and rawhides.

Don’t overfill trash cans — This goes for recycling containers, too.

Cover any compost bins — This keeps flies from accessing organic matter that they’re attracted to.

Avoid walking at dusk, dawn, and during hot mid-day hours — These times are when black flies are most active.

Stay away from shady, densely vegetated areas — Forests are prime habitat for black flies and other insects.

Cover your dog’s ears with a light-colored, folded bandana — Protective clothing creates a barrier to a sensitive area on your dog that black flies are attracted to. It may be a good idea to even spray the bandana with one of the pet-safe insect sprays listed below beforehand.

What to avoid when addressing black fly bites on your dog

Before you reach for an insect repellent, consider that products containing DEET and other insecticides carry risks. These chemicals are absorbed through your dog’s skin and can be ingested when your pup licks their fur. Similarly, essential oils may pose similar problems, and some — like cinnamon and citrus — are poisonous to dogs and cats.

Here are some of our recommendations for low-toxicity, dog-safe bug sprays that get a thumbs-up from vets:

The best course of action for black fly bites and other insect bites on your dog is preventive measures and ensuring that your pet never comes into contact with these pesky insects, but sometimes that can’t be avoided. If you find your pet with a bug bite, know that it’s completely normal and typically won’t cause any serious issues except itchiness.

Frequently asked questions

What do fly bites look like on a dog?

While they can occur on any part of your dog’s body, black fly bites can typically be found on the underside of the dog as well as the inner parts of your dog’s ears. Oftentimes they’ll present as red circles with a brighter dot in the middle similar to a bullseye. Large welts or other bite marks may be present, some with a bright red circle encompassing the bite. Know that even with a large number of bites, your dog will likely be okay, just uncomfortable.

How do I get rid of black flies on my dog?

Flies tend to gravitate towards strong odors, such as fecal matter or dirt, and one way to prevent the prevalence of black flies is to regularly groom your dog with baths and brushing. If your pet plays in your backyard or partakes in outdoor activities regularly, make sure that there is no fecal matter sitting around as flies tend to lay their eggs there, and always clean up trash and other waste from around your home and yard.

Another handy way to prevent your dog being bitten is to use hanging fly traps or citronella candles inside and outside of your home.

What can I put on my dog for fly bites?

If you have a favorite insect repellent that you like using on yourself, think twice before putting it on your dog. Pets are at risk for neurological and gastrointestinal issues if exposed to DEET, which is commonly used in insect repellents for humans. You can, however, use dog-safe bug sprays.

What is the best thing to put on black fly bites?

Fly bites will typically heal on their own without any vet intervention, but as with any skin lesion or injury, it’s important to keep the area clean and do your best to prevent your dog from licking, scratching, rubbing, or picking at the area.

How long does it take for black fly bites to go away on dogs?

The red spots and bites should go away in a matter of a few days up to a week, but if the bites are lasting longer, consider consulting with your vet as your pet may be experiencing an allergic reaction.

How can I prevent other insect bites?

In addition to black flies, you’ll want to be aware of other insects like sand flies, maggots, and fleas that can find their way to your dog’s skin. For example, an open wound on your pet may present the perfect opportunity for flies to lay their eggs.

One of the most important things to remember is to use effective methods like tick prevention medicine and consistent cleaning to ensure your pet stays safe.

What are symptoms of a severe insect bite?

While severe cases following insect bites are rare, your pet may present with symptoms like loss of appetite, a rash, weakness, or lethargy which could be an infection. More often than not, your pup will be on their way to healing in no time, but rare cases do occur so it’s important to always monitor your furry friend’s health and well-being.

What are the conditions under which my dog can get bitten?

In the spring and summer months, you may notice more tiny flies and other flying insects. To best avoid these parasites, stay away from livestock, standing water, and other large bodies of water as insects congregate in these areas.

Even with these precautions, you may find red dots or red bites on your pup as these insects can be persistent.

Can flies bite my cat?

Yes, especially if your cat goes outside regularly. As with dogs, be on the lookout for any adverse reactions and seek professional help if needed. Be aware that dog-safe doesn’t necessarily mean cat-safe, so always check that whatever product you wish to use on your pet is specifically approved for their species.