Why are Colorado rabbits growing tentacles and horns?

August 18, 2025

Rabbits with tentacles in northern Colorado.

There’s not really a better way to sum up recent photos and headlines about cottontail rabbits spotted around Fort Collins with long, dangling growths on their faces.

But as concerning as they appear, the virus that causes the dark, wart-like growths is relatively common and usually not anything to worry about, Colorado Parks and Wildlife officials said Wednesday.

Rabbit papilloma virus is a mostly benign disease that can impact cottontail rabbits in Colorado bitten by infected fleas or ticks. The virus does not spread to humans or pets and most rabbits clear the virus on their own — but not before strange wart-like growths pop up on their faces, as shown in this undated photo. (Courtesy of Colorado Parks and Wildlife)

A rabbit infected with the Shope papilloma virus, which causes wart-like growths that can look like horns, is seen in Fort Collins, Colo., on August 2025. (Courtesy of Amanda Gilbert via AP)

FILE – This June 26, 2013, image made from a video provided by Gunnar Boettcher shows a rabbit in Mankato, Minn., that Boettcher dubbed “Frankenstein,” due to what looks like horns growing out of its head. (Gunnar Boettcher via AP, File)

A rabbit infected with the Shope papilloma virus, which causes wart-like growths that can look like horns, is seen in Fort Collins, Colo., on August 2025. (Courtesy of Amanda Gilbert via AP)

This photo provided by the Iowa Department of Natural Resources shows a deceased Eastern cottontail rabbit infected with Shope papillomavirus in October 2021. (Iowa Department of Natural Resources via AP)

This Aug. 2025 photo provided by University of Kansas Biodiversity Institute shows a rabbit specimen with the Shope papilloma virus at University of Kansas Biodiversity Institute. (Courtesy of the University of Kansas Biodiversity Institute via AP)

1 of 6

Rabbit papilloma virus is a mostly benign disease that can impact cottontail rabbits in Colorado bitten by infected fleas or ticks. The virus does not spread to humans or pets and most rabbits clear the virus on their own — but not before strange wart-like growths pop up on their faces, as shown in this undated photo. (Courtesy of Colorado Parks and Wildlife)

Expand

The growths are caused by rabbit or shope papilloma virus, which is spread between cottontail rabbits through direct contact or biting insects such as fleas and ticks, Parks and Wildlife spokesperson Kara Van Hoose said.

Did a Gold Country peacock and turkey make a love match?

American crow with West Nile Virus infection found in Walnut Creek

Hundreds may have been exposed to rabies at bat-infested cabins in Grand Teton National Park

Travis Kelce’s love of otters earns him, Taylor Swift, Monterey Bay Aquarium invite

Western gulls hit with mystery illness found on California beaches

Shope papilloma virus can’t spread to humans or other pets, although both should avoid rabbits and other wildlife, Van Hoose said.

State officials have received a handful of reports of the virus since Denver’s 9News published a photo and story of the odd virus last week, which spread to dozens of other local, national and international news outlets.

The waxy papillomas are mostly made up of keratin and don’t have any negative impact on rabbits unless they interfere with their ability to eat or drink, and most rabbits recover from the virus.

Rabbit papilloma virus can spread to pet rabbits and is more severe in domestic breeds, so pet owners should seek veterinary treatment if their animal gets sick, state officials said.