What Kind of Bug Bite Leaves a Bruise? How to Identify

Bug bites are a fact of life, especially if you spend a lot of time outdoors. While allergies and other factors can lead to serious reactions, most bugs tend to cause mild symptoms like swelling and itchiness.

But depending on the bug and your individual reaction, bruising is possible. Bruising may occur from flying insects and from bugs that can burrow deep into your skin.

Find out more about the types of bugs that may cause bruising, what you should do, and how to identify the most common symptoms associated with certain bugs so you know when to seek medical treatment.

Should I be concerned?

A bruise from a bug bite isn’t usually a cause for concern. Most bug bite symptoms go away on their own within a few days.

However, if you know that a certain type of bug bit you, or if your symptoms worsen, you may need to see a doctor.

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The following types of bug bites sometimes cause bruising. Here’s what you need to know.

Hornets and wasps

Hornet and wasp stings are often painful.

After the sting occurs, the affected area of skin may be red and swollen. It may also look blue and purple due to the injury.

Such symptoms tend to resolve on their own within a few days without the need to see a doctor.

Mosquitoes

Mosquitoes are perhaps best known for leaving behind small, red bumps that are extremely itchy. Sometimes, these bumps may also darken, creating a bruise-like appearance.

As with hornets and wasps, mosquito bite bruises don’t usually require medical attention.

Spiders

Certain types of spider bites may also lead to bruising, including venomous ones like the brown recluse spider or black widow spider.

With this type of bite, you’ll notice rings around the site in varying colors, including red, blue, purple, and white. This is a result of skin necrosis from the venom, which destroys skin tissue.

Venomous spider bites require immediate medical attention.

Ticks

Ticks burrow deep in the skin, so you must carefully remove them by the head with a pair of tweezers.

When caught early, you may not notice any symptoms. Ticks can sometimes leave behind a red mark or bruise, which can also be swollen and itchy.

Aside from bruising, a bug bite may also cause redness and swelling (inflammation).

Even without a bruise, these symptoms may be present. Some insects, such as mosquitoes, may cause itchy bites.

Most symptoms are minor and will go away within a few days.

Signs of a more serious reaction

It’s possible for a bug bite to cause more serious reactions. Get medical attention right away if you experience signs of anaphylaxis, a serious allergic reaction that can cause:

• breathing difficulties
• facial swelling
• hives
• dizziness
• faintness
• confusion

You should also call your doctor if you experience symptoms of an infected bug bite, including:

• fever
• chills
• pus coming out of the bite
• swelling that continues to grow without improvement
• a red streak growing from the bite

A doctor will recommend home treatments to help alleviate mild bug bites. Follow these steps for bug bites with bruising:

1. First, wash the bug bite with plain soap and warm water. Pat (don’t rub) dry.
2. Apply cold compresses or ice to the affected area for 15 minutes at a time, multiple times a day. This helps alleviate pain and swelling. Repeat up to 48 hours after the bug bite.
3. Rest and elevate the affected area, if possible. This can help reduce swelling.
4. Switch to warm compresses after 48 hours to help reduce pain. Repeat as often as needed.
5. If your doctor says it’s OK, take a pain reliever such as acetaminophen (Tylenol) or a nonsteroidal anti-inflammatory drug (NSAID) like ibuprofen.
6. For itchiness, consider a topical hydrocortisone cream or an oral antihistamine such as diphenhydramine (Benadryl). Follow all product directions carefully.

If you have a more serious bug bite, it’s important to get the area checked by your doctor before attempting to self-treat.

If you don’t know what bug you’ve come into contact with, you may be able to make this determination based on the symptoms of your bite.

Here’s a roundup of the most frequent symptoms associated with common bugs in the United States:

Serious bug bites may sometimes lead to the following complications:

• Infections. Fever, rash, and pus at the site of the bite are all signs of infection. It’s important to quickly address a possible infection such as cellulitis.
• Lyme disease. Caused by tick bites, early symptoms of Lyme disease can include a fever and a rash that looks like a red bull’s-eye.
• Necrosis. This can occur in the case of brown recluse spiders, whose venom can kill healthy skin tissue and lead to lasting complications such as scars.
• Viruses transmitted by mosquitoes. These include the West Nile virus, yellow fever, the Zika virus, and malaria.

A bruise alone may not be a sign of the above complications. That’s why it’s important to see a doctor if:

• you have a bite that won’t improve
• you develop symptoms related to a venomous spider or tick

Bruises are caused by broken blood vessels brought on by trauma to the body. The black, blue, or purple areas of skin are a result of blood pooling underneath your skin.

Any type of injury or trauma can lead to a bruise. You might also be at risk for bruising based on:

• your age
• use of blood thinners
• bleeding disorders

Minor bruises don’t typically need medical attention. Severe bruising causes by more serious trauma such as car accidents may need to be evaluated for underlying damage.

Other types of bruises that may need further attention include those caused by bone fractures or a bleeding disorder.

Most bruises heal within 2 weeks, though more severe cases can take longer. See a doctor if your bruise doesn’t improve after 4 weeks, as it may be a sign of an underlying condition.

Bruising is just one of the many symptoms of a bug bite and is more common with some insects. Most cases are mild and can be treated at home.

See your doctor or another healthcare provider if you develop a severe reaction to your bug bite, or if the bruising doesn’t improve after several days.

You should also seek medical attention if you suspect a venomous or disease-carrying bug might have caused your bites.

7 Common Bug Bites on Dogs

Dogs can be bitten and stung by a variety of insects, so it’s important to know what the different insect bites look like on a dog. Not all insect bites need to be treated, but certain symptoms require immediate medical attention. Knowing how to protect your dog from these insects is also key to keeping your pet healthy.

Fleas

Fleas are tiny, dark brown insects that jump on a dog to feed on its blood. They are often carried in from outdoors, and once inside the house, they breed and multiply. Dogs will chew and scratch at their bodies when they are bitten by fleas due to the painful bite. The scratching and chewing can lead to self-trauma of the skin that causes scratches and sores to form. The bite of a flea can be difficult to see under a dog’s thick coat. Flea bites look like small, red spots on the skin, but sometimes it can be hard to tell their bite from the bite of another insect.

If you see insect bites on your pup, or notice that your dog is chewing and scratching a lot, the first thing to look for are flea dirt and live fleas. Flea dirt consists of fecal material and dried blood and looks like tiny, black flecks on the skin. Fleas and flea dirt are most often found on the lower back, tail, and on the hind legs of dogs.

Some dogs have an allergy to flea saliva, and one flea bite can lead to flea bite dermatitis. This skin condition causes intense itchiness all over, hair loss, and sores due to self-trauma. Bacterial and yeast infections can develop secondary to a flea allergy.

The best way to prevent and treat fleas is with flea and tick prevention. There are many types of flea and tick preventions available, such as topical products, flea/tick collars, and oral medication. Talk with your local veterinarian to decide which flea and tick product is best for your dog, and make sure to administer it year-round to keep the fleas and ticks away.

Ticks

Ticks are eight-legged parasites that like to hide in the grass, shrubs or woods. When a dog walks by they will crawl onto the dog’s body, usually on the legs or paws first before burrowing into the skin. They will then bite to suck blood from their new host.

A tick bite looks like a circular area of inflamed skin. The area is often red and slightly swollen after a tick is removed or falls off and crusts or a scab may also be present. The skin lesion may be itchy and irritating to your dog. As a natural reaction, dogs may want to scratch or lick at a tick bite after the tick is gone, and that causes the area to become infected. Occasionally, when a tick transmits Lyme disease, the tick bite looks like a red bullseye lesion on the skin. If you remove any ticks from your dog, especially if they were already attached to the skin, contact your veterinary hospital to get your pup started on flea/tick prevention immediately. Also, schedule an appointment to bring your dog in to be tested for tick diseases within two-to-three months after the tick bite or tick was found. It’s important to screen for tick diseases and provide treatment if a tick disease is detected. 

Check dogs daily for ticks, especially after they have been in an area where ticks are present. Ticks can be found anywhere on a dog’s body but are most common on the feet, neck, head, and ears. Some ticks can be found in the webbing between the toes or attached to the anus, so looking everywhere on your dog for ticks and tick bites is important.

To protect against ticks, dogs need to be on year-round flea and tick prevention plan. There are many types of flea and tick preventatives available that are applied differently. Ask your veterinarian which flea and tick prevention are the most effective and safest for your dog.

Mites

Skin mites, such as sarcoptic mange and demodex, are so tiny they cannot be seen by the naked eye. Their bites also are not visible. However, when there are enough mites in certain areas on a dog’s body, they will cause the fur to fall out in those spots, forming patchy areas of hair loss. These areas are extremely itchy if sarcoptic mange is present. Demodex does not cause itchiness but can lead to secondary bacterial infections, which can cause the skin to be itchy, red, crusty, or have pustules.

The mite that causes sarcoptic mange (aka scabies) is called Sarcoptes scabiei, and is highly contagious. Dogs get sarcoptic mange by being in contact with a fox or another dog that has these mites on its fur. Dogs can also spread sarcoptic mange to humans. 

The two mites that cause demodex on dogs are Demodex canis and Demodex injal. These mites are normal inhabitants on a dog’s skin. However, when a dog has a compromised immune system, due to being young or having an immune-mediated condition, these demodectic mites become plentiful and cause hair loss. If your dog shows any signs of mange, contact your veterinarian to schedule an appointment.

Sarcoptic mange can be prevented by keeping dogs away from foxes and infected dogs. Also, certain flea/tick preventatives protect against demodex and scabies, such as NexGard, Simparica, and Bravecto. Giving one of these products to your dog year-round will not only protect them from fleas and ticks but also skin mites.

Another type of mite that can be a nuisance to a dog is the ear mite known as Otodectes cynotis. These mites are contagious, so keeping your dog away from dogs and cats that have these ear mites will keep your pup protected. Ear mites only live within the vertical and horizontal ear canals, so their bites are not visible.

Mosquitoes

Mosquitoes are one of the most common flying insects and are found in most places around the world. They will bite and feed on dogs when they are outside but can also make their way indoors. A mosquito bite on a dog can appear red with a raised skin lesion—just like that of a human. Mosquitoes can bite a dog anywhere on its body, but they have an easier time biting areas where there is less fur, such as the ears, belly, inner legs, and groin region.

Mosquito bites do not need to be treated unless hives develop, which indicates an allergic reaction. If your pup is having an allergic reaction, call your local vet hospital for guidance. A major concern with a mosquito bite is the risk of heartworm disease. Not all mosquitoes carry heartworm disease, but those that are infected will transmit this parasite through a bite. It is crucial for dogs to be on year-round heartworm prevention to protect against heartworm disease.

Here are a few ways to protect your dog from mosquitoes:

• Have a pest control company come to your house and spray the yard with mosquito repellant. Find out from the company if there is a certain amount of time to keep your pets off the grass after the yard has been treated.

• Apply a pet-safe bug repellant spray on your dog’s coat before your dog goes outside, such as Vet’s Best Natural Mosquito Repellant Spray. This product is made of natural oils and can be sprayed on the coat every two hours as needed.

• Topical products, like Advantix II and Vectra 3D, protect against fleas, ticks, and mosquitoes. One dose lasts 30 days. These products are only labeled for dogs. Do not use on cats, as medications formulated for dogs are toxic to cats.

Bees/Hornets/Wasps

Stinging insects, including bees, hornets, yellow jackets, and wasps, can cause significant pain when they sting a dog. Dogs may cry out suddenly and lick the area where they were stung. If a dog gets stung on the paw or leg, they may start limping immediately. Most stings can cause localized swelling, pain, and redness. Applying an ice pack to the area for 5-10 minutes as needed can help provide comfort and reduce swelling. Call your veterinarian to ask if Benadryl should be given and at what dose.

Some dogs may have an allergic reaction when they are stung by a bee, hornet, wasp, or yellow jacket. Symptoms of an allergic reaction include:

Gastrointestinal symptoms including vomiting and diarrhea.

If these symptoms occur, this is a life-threatening emergency, and you need to contact your nearest veterinary hospital immediately.

Bees, wasps, hornets, and yellow jackets are prevalent during the warmer months, and they can be difficult to avoid. Their nests can be hidden from view in trees, on buildings, or under the ground. If you know there is a nest in your yard, keeping your dog away from that area will help.

Ants

Ants, especially fire ants, can cause a painful bite on a dog. The bite can look like a red, raised skin lesion and occasionally have a white center filled with pus, like a pimple. Applying an ice pack to the area can help reduce pain and swelling. If your dog was bitten by several fire ants, call your local veterinarian to ask if Benadryl should be given and at what dose.

Ant bites, most often from fire ants, can occasionally cause an allergic reaction, especially if a dog gets bitten by several ants at once. Facial swelling, hives, difficulty breathing, itchiness, moderate to severe swelling at the site of the bite, and gastrointestinal symptoms such as vomiting and diarrhea are all possible symptoms of an allergic reaction. If these symptoms occur, this is a life-threatening emergency, contact your nearest animal hospital immediately. 

It can be difficult to prevent your dog from being bitten by ants as these small insects can be hard to see in the grass and wooded areas. Check your yard regularly for ant hills and treat them, if found. Keeping your dog on a leash when walking or hiking can help guide your dog around an ant hill if you come across one. If you find ants on your dog’s body, brush them off as quickly as possible or rinse them off with water, if available.

Biting Flies

There are many biting flies that can leave a painful bite on a dog’s body, such as horse flies, deer flies, black flies, and sand flies. The bite can look like a red, raised lesion on the skin. Applying an ice pack to the area can help to reduce pain and swelling.

Some dogs are allergic to these flies and can have an allergic reaction when bitten. Facial swelling, hives, difficulty breathing, itchiness, moderate-to-severe swelling at the site of the bite, and gastrointestinal symptoms including vomiting and diarrhea are indications of an allergic reaction. If your dog experiences any of these signs, contact your local veterinary hospital as this is considered a medical emergency.

Keep Pups Safe When Outside

Biting and stinging insects are unavoidable, as they can be found anywhere outdoors and sometimes can make their way into the home. It is crucial to have your dog on flea and tick prevention year-round. Also, consider preventatives that can protect against mosquitoes and biting flies if these insects are prevalent in your area. Heartworm prevention is also essential to give to your dog year-round protection against heartworm disease transmitted by mosquitoes.

When outside, it is best to supervise your dog and check its skin for insect bites daily. Seek immediate treatment if you notice that your dog is displaying symptoms of an allergic reaction.

Featured Image: iStock.com/mixetto

WRITTEN BY

Michelle Diener, DVM

Veterinarian

I live in Raleigh, North Carolina. I obtained by BS degree in Biology at UNC-Chapel Hill in 2000 and my DVM degree at NCSU in 2006.