Squirrel Diseases

Bot Flies

Bot flies are obligate parasites during their larval stage, meaning they need a host to survive.  Larvae of the genus Cuterebra are commonly found in squirrels.  A female bot fly will lay her eggs in an area where a squirrel will encounter them, usually by a den site.

Once on the animal the increase in temperature causes the eggs to hatch. The hatched larvae will move through an opening on the body and into an area underneath the skin where they will develop for up to 7 weeks. During this time larvae are commonly called warbles. Each warble will create an opening in skin which allows it to breathe and will emerge from the same opening as a pupa. The pupa burrow into the ground during the winter months before becoming adult bot flies. Warbles are commonly noticed in late summer and early fall. 

Different genera of bot flies prefer different species as hosts such as rodents, horses, deer, and mink. Bot flies of the genus Cuterebra utilize rodents and rabbits.  The genus Cephenemyia affect deer. Learn more about bot flies in deer. 

A squirrel with warbles appears to have hairless growths with dark openings in the skin. Warbles look very similar to squirrel pox but can be distinguished by the opening at the top of each growth. One squirrel can be host to multiple warbles. 

Warbles need their hosts to survive so they are usually not lethal. Once the warble emerges, the opening in the skin heals. They can impact an animal’s health if there is a large infestation or the squirrel develops a secondary infection.

It is rare for people to have warbles. While uncommon, pets can be accidental hosts but they cannot get infected from other animals with warbles.

Squirrel Pox

Squirrel Fibroma Virus, sometimes referred to as Squirrel Pox, is a viral disease which primarily affects squirrels. The virus can be transmitted by biting insect vectors like mosquitos, or through direct contact with already infected animals. Because already infected squirrels can easily transmit the disease to other squirrels in the area, it is important to temporarily remove bird feeders (or other squirrel attractants) from your yard if you suspect that there are infected animals in your area.

Squirrel Fibroma virus primarily affects squirrels, with gray and fox squirrels being the most commonly affected species in North Carolina. The virus can also be transmitted to groundhogs and rabbits, although contraction of the virus is uncommon in these animals. There are many different species of similarly related viruses which can cause fibromas in other wildlife species, however these are typically species-specific viruses. Learn more about fibromas in deer.

The virus causes squirrels to develop growths and sometimes scabbing across their body. These growths typically have little to no hair on them and vary in size (they can be anywhere from 1/16 – 1 inch in diameter). Squirrel Fibromas are similar in appearance to cutaneous warbles from bot flies but can be distinguished from warbles because they do not have large black openings in the center of the growths.

In some cases, squirrels can fight off a mild infection and can recover from the virus with no permanent side effects or growths. In more severe cases, animals will likely be unable to fight off the infection, and the virus will lead to emaciation and eventual death.

Humans, cats, and dogs cannot contract squirrel fibroma virus. Although uncommon, it is possible for domestic or pet rabbits to contract the disease.