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Botflies, which are also called warbles, can advance to a cuterebra stage, or embed larvae under your beloved dog’s skin, in their upper respiratory tract, eyes, and even their central nervous system. This pesky and even dangerous— if left untreated— parasitic condition is also sometimes called wolf worms when it’s in the larval stage of development.1
Thankfully, you are not without a way to help your furry friend fight back against these unpleasant interlopers. Read on to learn more about botflies, how to spot them, and how to get treatment.
- What Are Botflies?
- Signs of a Botfly Infestation
- Symptoms of a Botfly Skin Infestation
- How to Remove Botflies From a Dog
- Final Notes
What Are Botflies?
Botflies come from the family Cuterbridae and they are a parasite that attacks mammals. They look sort of like bees, but they are hairy and without bristles. They also do not bite or feed. Their hosts are usually rodents and rabbits, but dogs can get warbles if they are infested with larvae as the rabbit type of cuterebra isn’t as host-specific. Meaning, these flies will welcome a new host if one presents itself. Generally, they are most active in the early fall, and late summer time of the year when adult insects are most active.1
Females deposit eggs near the openings of animal burrows, nests, and along the runways of their typical hosts, in addition to in vegetation and on stones. Throughout her lifetime, a female botfly will lay or deposit between 5 and 15 eggs per site and is responsible for more than 2,000 eggs.2
Animals, like your dog, can become infested with botflies when they walk or lay in contaminated areas. They are most at risk if they hang out in an area where botflies lay their eggs, like rabbit burrows and other similar locations.
Next, once the eggs hitch a ride on your dog, they hatch onto the host’s body in response to their heat. The botfly on dog larvae can enter the body in a few ways. They most often enter through the mouth, nose, ears, or during grooming, the nares. However, they can also enter through open wounds, but this isn’t nearly as common. Once inside the host, the larvae migrate to various locations within your dog’s body where it will access air via a breathing pore, as well as continue to develop into its final stage. This process takes about 30 days, then the larvae simply exit your dog’s skin (or other host) and fall to the soil to pupate.
The larvae of the botfly are short, segmented grubs that live in the tissue of animals. Under the skin, this type of parasite forms a bulge or small lump in the skin. Also, as mentioned above, these larvae will create a breathing area and extend a breathing tube. The adult variety of botflies are often confused with other types of flying insects such as flies and bees. The adult length is about 1 inch but this will vary based on the species of fly.
Virtually no state in the nation, excluding Alaska, is without botflies. In addition, botflies have been found in Mexico and Canada. There are 34 Cuterebra species in North America alone. Therefore, it’s important to know the signs of botfly larvae in dogs, or an infestation as well as learn ways to prevent your dog from coming into contact with this parasite in the first place in an effort to keep them botfly-free.
Signs of a Botfly Infestation
Obviously, the type of symptoms you might notice if you suspect warbles will vary based on where in the body the cuterebra infestation occurs. The following will show the symptoms associated with specific areas of the body being infested. Knowing these symptoms will help you identify what to look for if you suspect botflies.2
Symptoms of a Botfly Skin Infestation
Warbles are often the most common type of botfly infestation, so make sure you keep an eye out for these symptoms of a botfly skin infestation:2
- Swelling often around the neck or face
- Lack of appetite
Symptoms of an Upper Respiratory Tract Botfly Infestation
Another potential location for botflies to migrate to is the respiratory tract. This can cause all sorts of problems as you might imagine, with symptoms including:2
- Nasal discharge
- Nasal or facial swelling
- Difficulty breathing
- Increased breathing rate
Symptoms of an Eye Botfly Infestation
The eyes are not without risk when it comes to botflies. In fact, they can infest this sensitive area just as they do the nose/respiratory system, skin, and other locations. Look for these symptoms to indicate that your dog has an eye botfly infestation:2
- Inflammation in the inner eye area
- Eyelid swelling
- Eye discharge
- Pink eye also called conjunctivitis
Symptoms of a Spinal Cord or Brain Botfly Infestation
Last but certainly not least, botflies can even infest your dog’s nervous system, meaning their spinal cord and brain. Look for the following indicators that this might have occurred:2
- Head pressing
- Low body temperature
- Head tilt
- Abnormal behavior
General Symptoms to Look For
If you aren’t sure about the location but suspect your dog might have come into contact with a botfly, look for the following general systems that could indicate an infestation is present:2
- Matted coat
- Neurologic signs (mentioned above)
- Swelling around the site of infection
- Visibly seeing the larva or foreign body
How to Remove Botflies From a Dog
Now that the ugly reality of what a botfly infestation can do to your beloved friend has been laid out, you likely want to know what to do to get rid of these pests. The short answer is you cannot and should not remove the botflies yourself. Instead, consult a veterinarian who will manually remove the larva from your dog and then clean the wound.
In some cases, your dog might need antibiotics to treat any secondary infections they may have experienced as a result of their infestation. The reason why you should never attempt to remove a botfly from your dog is that if you remove the larvae and squeeze it wrong, it could rupture, causing an even bigger problem like another infection. Therefore, it’s important that you let the professionals handle a suspected botfly infestation both in terms of diagnosing it and then treating it long-term.2
When visiting your vet, expect them to look for evidence that there is an infestation in the respiratory tract or on the skin. Sometimes, dogs with infestations will only present with symptoms on one side of their body, such as swelling only on one side of their face, or nasal discharge only on one side, etc. In many cases, your dog will need to be thoroughly examined to look for indicators of fly larvae. This typically requires them to be put under general anesthesia. When it comes to more severe cases where the infestation is in the nervous system, then MRIs, spinal taps, or CT scans might also be used to look for indicators of infestation.2
If an infestation is found in the spinal cord or brain, then instead of manually removing that larva, your vet will likely put your dog on medication like Ivermectin. This is a type of medication, like a dewormer, that is used for heartworms and has been shown to stop the progression of symptoms, but it might not heal any existing problems. If the botfly can be removed, then it’s important to keep monitoring the area for swelling, discharge, or other indicators that it is not healing properly. When it comes to brain and eye infestation, the healing process can take weeks if not months.2
How do you know if your dog has a botfly?
Look at the symptoms listed above under each type of infestation. If your dog has any or several of the symptoms, it is likely a good idea to contact a professional as soon as possible to look for a diagnosis and treatment of the infestation.
Can humans get botflies?
Yes, you as a human can get botflies. However, the good news is that you cannot get the infestation from your dog because once a botfly has made its way inside your dog’s body, it cannot be transmitted to another host, human or otherwise.
Do botflies exist everywhere in the United States?
Yes. As mentioned above, there are botflies in every state of the nation except Alaska. So, your dog is at risk for this if you live anywhere but Alaska.
Can you prevent your dog from coming into contact with botflies?
Yes and no. You can reduce their risk by keeping your dogs away from burrows and rodent nests, which are the most likely places they will come into contact with botflies. However, you cannot prevent them from ever venturing on their own, so it’s a good idea to check your pet regularly for signs of botflies. This is especially important if you live in an area that is considered high-risk.
Thankfully, with proper treatment and early intervention, botfly infestations generally have a good prognosis. Therefore, especially if you live in an area with lots of rodents or rabbits, consider checking your dog regularly and pay attention to even small changes in their behavior to get ahead of this issue.
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“Botflies in Dogs (Cuterebra in Dogs).” PetMD, www.petmd.com/dog/conditions/infectious-parasitic/c_multi_cuterebrosis. Accessed 20 July 2023.
Moriello, Karen A. “Cuterebra Infestation in Dogs and Cats - Integumentary System.” Merck Veterinary Manual, 19 July 2023, www.merckvetmanual.com/integumentary-system/cuterebra-infestation-in-dogs-and-cats/cuterebra-infestation-in-dogs-and-cats.