How to keep biting flies off your dog

Biting insects can be extremely bothersome, and in some cases, dangerous. Mosquitoes, black flies, no-see-ums and deer flies — they all exist in Maine, and they can really make a mark on your skin and your sanity.

Unfortunately, the same goes for your dog.

There’s nothing quite so pathetic as a pup’s belly covered in blackfly welts, or a dog nipping at the air, trying to get rid of a relentless mosquito.

Though a dog’s fur can protect much of its body from most biting flies, there are some places — such as the stomach, chest, ears and face — where less hair makes biting easier. In addition, there are certain flies — such as deer flies — that can find skin through quite a bit of fur, pestering a dog to no end.

First – what NOT to do

To combat biting flies, people have concocted a wide variety of repellents using artificial chemicals and natural materials. But many of these repellents aren’t safe for dogs.

Dogs tend to lick themselves, which means they ingest whatever coats their fur.  In addition, some substances used in insect repellent — even certain essential oils — can poison a dog right through their skin.

“At high dosages, [certain oils] can cause severe toxicity, so you have to be pretty careful,” said Dr. Ai Takeuchi, a veterinarian at Lucerne Veterinary Hospital in Dedham. “Tea tree oil is one that a lot of people use in high doses and can cause such a severe allergic reaction in dogs that it can cause liver failure.”

Photo by Aislinn Sarnacki

Tea tree oil is often used in natural insect repellents. It’s also used by people to treat skin problems. So it’s easy to see how people would assume it to be harmless for dogs.

“Something that’s natural or thought of as non-chemical doesn’t always equate to safe,” said Dr. David Cloutier, a veterinarian at Veazie Veterinary Clinic in Veazie. “I’m cautious about anything I’m putting on my dog’s skin.”

Other essential oils that are toxic to dogs and most frequently cause problems include pennyroyal oil, oil of wintergreen and pine oils, according to a Pet Poison Helpline article written by Jo Marshall, a senior veterinary information specialist. In addition, cinnamon oil, citrus oils, peppermint oil, sweet birch oil and ylang ylang, can be poisonous to dogs in high enough doses, according to an article published by the American Kennel Club.

Keep in mind, that’s far from a complete list. That’s why it’s important to consult your veterinarian before using products that are intended for people on your dog.

“I’ve treated a patient or two where owners made their own concoctions with essential oil and sprayed it on the dog and it was too concentrated,” Takeuchi said. “Unfortunately, one of those dogs did pass away. You have to be very careful. I don’t recommend making your own stuff because you just don’t know what’s safe.”

Oreo in the woods

Safe ways to keep insects off your dog

Topical treatments that repel fleas, ticks and biting flies are frequently suggested by veterinarians as the first line of defense. These liquid treatments contain synthetic chemicals, such as permethrins, at safe doses for dogs within specific weight brackets. Effective for months at a time, these topical treatments are typically applied to the back of a dog’s head and down its upper back, where it can’t be licked away. And these treatments are not safe for cats.

“I always read directions on [topical treatments] and make sure I have the right size because there are different weight categories,” Cloutier said. “And there are very distinct differences between dog and cat products. Cats can’t clear permethrin.”

Takeuchi suggests a topical treatment called Vectra 3D, which is known as a flea treatment but is also effective against mosquitoes, ticks and biting flies. However, you can work with your veterinarian to acquire their suggested brand.

“The only problem is with topical stuff, if your dog is swimming, it can dilute it out by the end of the month,” Takeuchi said.

Oreo wading in Pushineer Pond.

In addition or as an alternative to a topical treatment, there are a few natural insect repellents that have been formulated specifically for dogs.

Takeuchi suggests VetriScience repellent spray and wipes, which are made out of essential oils in quantities that are safe for dogs, Takeuchi said. The top essential oil in these products is lemongrass oil, and it only accounts for 3-4 percent of the repellent. Cinnamon, sesame and castor oils are also in the ingredient list.

In addition, the Maine-made Skeeter Skidaddler Furry Friend insect repellent is made specifically for dogs. The ingredients include cinnamon, eucalyptus, lemongrass and sunflower oils.

Last but not least, you can treat dog clothing — such as a bandana, dog vest or harness — with permethrin spray or DEET, two chemicals most commonly used to repel flies. Be sure to give these chemicals plenty of time to dry. The idea is to not get them on your dog’s skin.

If you don’t feel uncomfortable treating the clothes yourself, the Maine company Dog Not Gone offers insect repelling dog vests and bandanas made with No FlyZone material, which has undergone a special treatment that binds permethrin to the fibers of the fabric. In addition, Insect Shield makes dog vests and bandanas that are similarly pre-treated with permethrin through a special process.

This method of protection — treating clothing with chemicals — may be the only way to discourage more aggressive flies, such as deer flies and horse flies, which in Maine emerge later in the season.

Deer fly. BDN photo by Scott Haskell

An interesting fact about bug bites on your dog

Back fly bites are often mistaken as tick bites. This is because black fly bites often cause a ring-shaped bruise on a dog, and this mark looks similar to the bull’s-eye rash that some people develop after being bitten by a deer tick and contracting Lyme disease.

“99 percent of the time, it’s a black fly bite,” Takeuchi said. “We get a ton of emails and phone calls every day about this. And there are scary things that can cause bruising like that on your animal, like rat poison, so we always tell them to shoot us a photo.”

“The bruise has more of a purplish color than a red color, and it’s maybe the size of a dime,” Cloutier said. “It’s usually on the lesser-haired parts of the body. So if your dog rolls over for a belly rub and you see them, they’re usually black fly bites.”

While mosquitoes bite dogs, they don’t leave a lesion, Cloutier said. And they the bites don’t seem to bother dogs or itch as much as they do for people. Regardless, I think we’d all agree that it’s best to not let your dog be eaten alive out there. So let’s test out some of these insect repelling techniques.

An adult mosquito harvesting a blood meal. Courtesy of Griffin Dill

Let me know what works best for you in the comments below. And if I’ve forgotten something, please share! Often the comment section is just as useful to readers as what I drum up for my post.

Aislinn Sarnacki

About Aislinn Sarnacki

Aislinn is a Bangor Daily News reporter for the Outdoors pages, focusing on outdoor recreation and Maine wildlife. Visit her main blog at