Bug bites are a common occurrence in dogs due to both their proximity to the ground and their tendency to stick their nose in things. Many bug bites are harmless and may even go unnoticed. Some bug bites are prone to triggering the immune system, causing the cells in the immune system to release histamine.

Allergic reactions to insects can range from mild bumps and itching to a potentially life-threatening anaphylactic response. An epi-pen may be prescribed for severe allergic reactions.

The allergic reactions to insect bites and stings can range from mild to critical. 

Critical reactions (anaphylactic shock) 

If your pet’s symptoms progress from mild to moderate, contact your veterinarian and take your pet to the nearest veterinarian or emergency animal clinic right away. Symptoms of insect allergy can move from moderate to fatal in a very short amount of time.

Several types of insects can induce an allergic reaction:

Biting insects - With biting insects, such as fleas, bedbugs, and ants, it is generally the proteins in the saliva that produce the allergic reaction. The most common bug related allergy in canines is an allergy to the saliva of the flea. Yellowjackets and wasps may also bite as well as sting. 

Stinging insects - Insects such as bees and wasps use a stinger full of venom as a defense mechanism. The allergy to the venom is what causes the swelling around the site of the sting and the other symptoms associated with a sting. Some types of ants can sting as well as bite. 

Ticks - Ticks are uncommon in that the allergic reaction may take several days to emerge. Ticks are also a common vector for disease and should be removed quickly and carefully, but it is important not to leave any parts of the tick embedded in the skin. 

Spiders - There are only a few poisonous varieties of spider in North America, the Black Widow, the Brown Recluse, and the Hobo Spider. The venom or saliva or of any spider can become an allergen, and even non-toxic spider bites should be watched for additional signs of allergy.

When specialized immune cells in the dog’s body, called mast cells, react to a protein that it has identified as a threat by releasing histamine, an allergic reaction occurs. Histamine is a naturally occurring chemical that binds to multiple types of receptors in the body and has an inflammatory effect on the tissues it comes into contact with. The release of histamines into the dog’s bloodstream results in the itchy and inflamed skin conditions characteristic of most allergic reactions in canines.

With insect bites and stings, the allergen is injected directly into the body, so the allergic response to the saliva or venom is usually rather rapid. The timing of the symptoms combined with the results of a thorough physical evaluation by your veterinarian should lead to a preliminary diagnosis of allergy, and many types of insect bites can be identified visually.

If the bug that bit the animal is not easily identifiable, routine blood tests are likely to be ordered. A complete blood count and blood chemistry panel will help to ensure that there are no toxins in the bloodstream and to check for the presence of enterocytes, which are a specialized type of white blood cell which can indicate a recent immune reaction to an allergen. Confirmation of an allergy will generally be followed up with an intradermal skin test to determine which allergen is responsible for the reaction. During an intradermal skin test, also called a patch test, minuscule amounts of the suspected allergens are injected under the skin in order to induce a localized reaction for further identification.

Treatment for symptoms of anaphylactic shock will likely begin even before a definitive diagnosis is received. Epinephrine is administered as soon as possible, and supportive therapies, such as IV fluids and oxygen, are likely to be offered as well. If your dog has a reaction to a bug bite and you have to use an EpiPen to stop the reaction, it is important to note that you will still need to bring the animal in for supportive therapy. Antihistamine or hydrocortisone shampoos and salves are often applied to relieve the swelling and irritation for milder reactions, but caution should be employed during application as ingestion of hydrocortisone can cause your pet gastric distress. Medications such as corticosteroids, administered by injection or oral ingestion, are usually quite effective in reducing the symptoms associated with an allergic reaction, but they are only recommended when alternate treatments have already failed as they have some serious side effects.

Injected immunotherapy may be another option for canines that are allergic to some insects and arachnids, especially with reactions that are resistant to antihistamines. Once the active allergens have been verified by the intradermal reaction test, an injection is designed with altered antigens prepared specifically for your pet. This personalized formula is injected on a weekly or monthly basis and  desensitizes the patient to the offending allergen or allergens. This method of treatment can be expensive and  time-consuming, but it has a high overall success rate, especially in younger dogs.

If your canine family member has a moderate to severe reaction to an insect or arachnid bite, your veterinarian may write you a prescription for an EpiPen to administer if your pet has a critical response to an allergen in the future. The device prescribed to your dog will have size appropriate dose of epinephrine for your dog. Dogs over 45 pounds are generally prescribed the same EpiPen as an adult human and dogs between 20-45 pounds will find the EpiPenJr amount to be more appropriate. Animals smaller than 20 pounds will usually be given a syringe with the right sized dose for their weight. Use of an EpiPen should be followed by a trip to the emergency room, even if your dog appears fully recovered. Epinephrine is a short-acting drug, and the allergic reaction may resume without proper medical treatment.