Do Mosquitoes Bite Dogs? Yes, and Heartworm Is Why It Matters

Do mosquitoes really bite dogs?

Yes. The Merck Veterinary Manual notes that many mosquito species often feed on dogs. In a laboratory study published in BMC Veterinary Research, sedated dogs were each exposed to about 50 unfed female Aedes aegypti mosquitoes for 60 minutes. On one beagle, 46 of them had taken blood by the end of the hour.

Only the females do it. Merck explains that female mosquitoes take a blood meal so they can lay eggs, the same reason they bite people (there is more on how male and female mosquitoes differ in a separate explainer). Merck adds that large swarms can take enough blood to cause anemia in domestic animals. For a pet dog the bigger concern is what the mosquito can leave behind.

Where do mosquitoes bite dogs, and when?

Wherever they can reach skin, and mostly around dusk and dawn. The timing is documented; the body sites are not. None of the veterinary sources used for this page maps where on a dog mosquitoes feed. Thinly haired skin, such as the ear flaps, the nose and the belly, is a reasonable guess and no more than that. The closest evidence is indirect: the BMC Veterinary Research report notes that in cats that react to mosquito bites, the skin signs most often appear on the ear flaps, face and paws. In the dog study, the one animal that reacted swelled at the base of the muzzle and around the eyes, which shows where the reaction appeared, not necessarily where the mosquitoes fed.

A thick coat is not a reason to relax. Whether long hair reduces bites has not been measured in those sources either, and heartworm guidance makes no exception for coat type: the American Heartworm Society (AHS) says all dogs should be tested every year. Living indoors does not settle it. The society points out that infected mosquitoes can come inside, so both outdoor and indoor pets are at risk.

The when is better established. The American Heartworm Society's canine guidelines name dusk and dawn as peak mosquito feeding times and recommend limiting a dog's outdoor activity then. Merck likewise advises against walking pets in the early morning or early evening, when adult mosquitoes are most abundant. Timing varies by species and season, which this breakdown of when mosquitoes are most active covers in more detail.

The guidelines name carbon dioxide, which animals breathe out, as one of the attractants that draw mosquitoes in. Whether a porch light makes things worse is a separate question, answered in the guide to whether mosquitoes are attracted to light. For the yard as a whole, see the backyard mosquito control guide.

What do mosquito bites look like on a dog?

Often like nothing you would notice. A mosquito feeds and leaves its host within 3 to 5 minutes, according to the BMC Veterinary Research report, and a small bump under a coat is easy to miss. The authors contrast this with fleas and ticks, and suggest the quick feeding may explain why severe reactions to mosquito bites are poorly documented in dogs.

When a bite does show, the signs to look for are redness and swelling at the bite site, which is how the report describes an allergic skin reaction to a bite. A stronger reaction is possible, though that report documents only one. Of the 28 dogs in that study, one developed an acute allergic reaction within 40 minutes of its second exposure to mosquitoes: a swollen face, most obvious at the base of the muzzle and around the eyes, with red eyes and swelling of the membrane lining one eye. Staff treated the dog at once and it improved within a few hours. The other 27 dogs showed no hypersensitivity.

Two cautions about that finding. It is a single case from a company-funded laboratory study in which dogs were exposed to dozens of mosquitoes at once. And the authors wrote that they knew of no earlier published data on allergic responses to mosquito bites in dogs. Nobody can yet say how often this happens to a pet in a backyard.

Why do mosquito bites matter for dogs?

Because a mosquito bite is the only way a dog gets heartworm. The FDA states that heartworm disease is spread only through the bite of a mosquito. It is not contagious, so a dog cannot catch it from being near an infected dog. The parasite is a worm, Dirofilaria immitis, whose adults live in the heart, lungs and associated blood vessels. The FDA describes the result as severe lung disease, heart failure, damage to other organs and death.

How a bite passes heartworm on

1. A mosquito feeds on an infected dog, or on a wild carrier such as a coyote or fox, and takes in microscopic young worms called microfilariae with the blood.
2. Inside the mosquito those young worms become infective larvae. The AHS guidelines put this at about 10 to 14 days at roughly 80°F and longer in cooler weather; in the three mosquito species studied, development stops below 57°F (14°C).
3. When the mosquito feeds again, larvae are left on the dog's skin and enter through the puncture wound the mosquito made.
4. Over about 6 to 7 months the larvae migrate through the body and mature into adult worms. The FDA gives adult males as about 4 to 6 inches long and females as about 10 to 12 inches.
5. The adults mate and the females release new microfilariae into the dog's bloodstream, ready for the next mosquito. Inside a dog, a heartworm lives 5 to 7 years.

The FDA puts the average worm burden in an infected dog at 15 worms, with a range of 1 to 250. Not every mosquito is carrying larvae: survey studies cited in the AHS guidelines found heartworm in 2.1% to 19.4% of trapped mosquitoes. Those rates come from different locations, and a dog that is bitten all summer faces that chance again with each bite.

Where heartworm occurs

In every state, though not evenly. The FDA says heartworm disease is most common along the Atlantic and Gulf coasts, from the Gulf of Mexico to New Jersey, and along the Mississippi River and its major tributaries, but it has been reported in dogs in all 50 states. Even the far north is not exempt. The AHS guidelines note that parts of Alaska have the mosquito species and climate to support transmission for brief periods, and that pet dogs from outside the state have tested positive there. If you are traveling north with a dog, here is what mosquito season in Alaska involves.

Signs of heartworm disease in dogs

Often there are none for a long time. The American Heartworm Society says that in the early stages many dogs show few symptoms or none at all, and the FDA notes that symptoms may not be obvious in dogs that have low worm burdens, were recently infected or are not very active. As the disease advances, the society lists a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite and weight loss. Dogs with large numbers of worms can develop a sudden blockage of blood flow within the heart, called caval syndrome, which is life-threatening.

An infection also cannot be detected right away. The FDA puts the earliest point at which a blood test can pick up heartworm proteins at about 5 months after the infecting bite, and the society says heartworms must be about 7 months old before the infection can be diagnosed. A dog can look healthy and test negative for months after the bite that infected it. A cough or a drop in stamina in a dog that has missed preventive doses is worth a call to the veterinarian.

Can dogs catch West Nile virus or Zika from mosquitoes?

West Nile only rarely, and it is not known to make dogs sick; Zika, not as far as anyone has shown. Merck says dogs and cats are rarely infected with West Nile virus through a mosquito bite and remain without symptoms, and that there is currently no evidence that dogs or cats can become infected with Zika virus. Heartworm is a different order of problem. The AHS guidelines describe it as causing more illness and death than any other vector-borne disease affecting dogs in the United States, which is why the rest of this page is about it.

How do you protect a dog from heartworm?

With a prescription preventive from a veterinarian, given all year. The FDA says many products are approved to prevent heartworms in dogs and all of them require a veterinarian's prescription. Most are given monthly, as an oral tablet or a liquid applied to the skin, and one is injected by a veterinarian every 6 or 12 months. These drugs prevent infection. They are not repellents, and the FDA is clear that they do not kill adult heartworms.

Testing comes first for most dogs. Dogs 7 months and older should be tested before starting, because giving a preventive to a dog that already has adult heartworms may be harmful or deadly, the FDA warns. Puppies under 7 months can start without a test, according to the American Heartworm Society, and its guidelines say puppies should start no later than 8 weeks of age. After that the society's rule is Think 12: test every 12 months and give the preventive 12 months a year.

Late doses are the usual weak point. The guidelines say a dog can become infected after just one skipped or delayed dose, and that the vast majority of reported preventive failures can be linked to lapses in giving the drug, although drug-resistant heartworms have also been documented. If you miss one, the society's advice is to call your veterinarian, restart the preventive right away and retest 6 months later.

Year-round dosing can look excessive where winters are cold. The guidelines' reasoning is that transmission drops in colder months, but warm pockets in urban areas suggest the risk never reaches zero, and some mosquito species survive winter as adults. They also recommend year-round dosing because it is likely to improve compliance.

Prevention is far easier on a dog than treatment. The FDA says treating heartworm disease can be toxic to the dog's body and cause serious complications, and that it is expensive because it takes multiple veterinary visits, blood tests, x-rays, hospitalization and a series of injections. The same visit is also a good time to ask about ticks, since the FDA notes that some heartworm preventives include ingredients against other parasites; a companion guide explains what to do about ticks on dogs.

Can you use human bug spray or DEET on a dog?

No. The American Heartworm Society's guidelines state that DEET is not recommended for dogs because it is approved for human use only.

The National Pesticide Information Center reports that pets overexposed to DEET have shown vomiting, shaking, excitement, lack of coordination and seizures. It also says reports of pets being exposed to enough DEET to make them sick are rare. Even so, putting a human product on a dog on purpose is the thing to avoid. If your dog gets into a repellent or shows any of those signs, call your veterinarian. NPIC also answers pesticide questions by phone at 800-858-7378.

Repellents for your own skin are a separate subject, covered in the guide to keeping mosquitoes away from people and patios. Apply yours away from the dog, and store the container where a dog cannot chew it.

What about repellents made for dogs?

They exist, and they are an addition to a heartworm preventive, never a substitute. The guidelines recommend FDA- or EPA-approved products designed for use in dogs. They describe two laboratory studies in which a permethrin-based repellent was more than 95% effective at preventing mosquito feeding, and they add that more studies are needed to show how it performs under field conditions. They also state that repellents and insecticide products, alone or together, are not completely effective by themselves where heartworm is highly endemic.

Merck names a combination of imidacloprid and permethrin, and a spot-on combination of fipronil and permethrin, for dogs, and warns that these products must not be used on cats. In a home with cats, raise that with your veterinarian before you buy anything. Use a product only on the species, age and weight range printed on its label, and follow the label for how often to reapply.

How do you cut down mosquitoes around a dog's yard?

Start with standing water, because that is where mosquitoes breed. The AHS guidelines treat mosquito control as part of heartworm prevention and list measures a dog owner can act on:

• Eliminate standing water. Empty anything that collects water, including the dog's own gear: wading pools, toys left on the lawn and outdoor bowls that sit unchanged. A separate explainer shows how quickly standing water breeds mosquitoes.
• Treat water you cannot drain. The guidelines name insect growth regulators, bacterial products based on Bacillus species, and mosquito fish. Use any product as its label directs.
• Shift the schedule. Limit walks and yard time at dusk and dawn, and steer clear of known mosquito habitats.
• Run a fan. The guidelines call fan-generated wind a practical way to protect people and pets in a backyard, because it disturbs mosquito flight and dilutes attractants such as carbon dioxide.
• Consider sprays and traps. Local insecticide sprays or fogs and adult mosquito traps are other approaches the guidelines mention, and they note that municipal programs and private professionals can provide guidance. Any insecticide has to be used as its label directs.

For the full method, see how to get rid of mosquitoes in a yard. If you hire a yard treatment, ask how long pets should stay off treated areas and what the product label says; this article on yard mosquito sprays around kids and pets lists the questions to raise.

Fewer mosquitoes means fewer bites, not zero. Yard work and dog-labeled repellents lower the number of bites; the preventive your veterinarian prescribes is there for the bites that still happen.

This guide is general educational information, not medical advice. If you have symptoms or concerns after a bite or exposure, contact a healthcare provider.

Frequently Asked Questions

Sources

1. Keep the Worms Out of Your Pet's Heart! The Facts about Heartworm Disease — U.S. Food and Drug Administration
2. Heartworm Basics — American Heartworm Society
3. Canine Heartworm Guidelines: download page for the Canine Guidelines for the Prevention, Diagnosis, and Management of Heartworm (Dirofilaria immitis) Infection in Dogs (revised 2024) — American Heartworm Society
4. Aedes (Stegomyia) aegypti mosquito bite hypersensitivity in a dog: a case report — BMC Veterinary Research (2020), via PubMed Central
5. Mosquitoes of Animals — Merck Veterinary Manual
6. DEET Fact Sheet — National Pesticide Information Center

How this guide was made: it was researched and drafted with AI assistance from the sources listed above. A second, independent AI pass then checked each factual claim against those sources. Found an error? Email support@buzzskito.ca.