Rabbits With ‘Horns’ Seen in Colorado Are Going Viral. Here’s What’s Really Happening

Though the strange growths on these animals may look intimidating, experts say there’s not much to worry about, and they’re caused by a fairly common virus

Amber X. Chen | AAAS Mass Media Fellow

August 15, 2025

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Tentacled monsters? Demon bunnies? Franken-bunnies? Rabbit mutants? 

Sightings of rabbits in northern Colorado with horn-like growths coming from their heads and near their mouths have recently stirred interest—and disgust—among local residents and across social media. 

“It looks like it was black quills or black toothpicks sticking out all around his or her mouth,” Susan Mansfield, a resident of Fort Collins, Colorado, who saw one of these rabbits, tells Amanda Gilbert of KUSA, which first reported the story.

The truth behind these sightings and pictures, however, is far from all the supernatural speculation. The rabbits are infected with cottontail rabbit papillomavirus, also known as the Shope papillomavirus, named after Richard E. Shope, who identified it in 1933. Shope was also the first to identify the influenza A virus and one of the earliest to link it to the 1918 flu pandemic, Stephanie Pappas reports for Scientific American.

But while the horns might look crazy, experts say the disease these rabbits have is actually pretty harmless. The curious growths are composed of keratin, which also makes up hair and nails. Kara Van Hoose, a spokeswoman from Colorado Parks and Wildlife, tells the Associated Press’ Ben Finley and Colleen Slevin that the immune systems of infected rabbits are typically able to fight off the virus, after which their “horns” will fall off.

Moreover, it is not contagious and only impacts rabbits and hares. Rather than transmission between rabbits, the disease is spread via fleas, ticks and mosquitos—and exposure to these insects peaks in the summertime. So, infection rates tend to rise around this time of year before dropping off again.

Horned rabbits became an internet sensation after the sightings in Fort Collins, about 65 miles north of Denver. But Van Hoose tells Scientific American that it’s unclear whether there is really an upsurge in infections this year. Locals may be reporting multiple sightings of the same rabbits. 

The history of human fascination with this disease may go back hundreds of years. The Associated Press reports that cottontail rabbit papillomavirus likely played a role in the jackalope myth. Originating in North America, the “jackalope” is a made-up creature described as a rabbit with horns or antlers.

In a low portion of cases, the papillomavirus could lead to squamous cell cancer in rabbits, per Scientific American. Infections are more dangerous in domestic rabbits, which could contract the virus via biting insects, and these rabbits should be treated by veterinarians, per Colorado Parks and Wildlife.

Additionally, research on the virus in rabbits has informed advancements in understanding the connection between the human papillomavirus (HPV) and certain cancers. This research, pioneered by Shope, later led to the development of the HPV vaccination.

The New York Times’ Hannah Ziegler reports that even though people can’t get the virus from infected rabbits, they should avoid interacting with the animals and opt to admire them from afar. 

“Nature is metal,” Van Hoose tells the New York Times, “and this can be kind of cool-looking on different rabbits.”

Amber X. Chen | Read More

Amber X. Chen is the 2025 AAAS Mass Media Fellow for Smithsonian magazine. She is an undergraduate at UC Berkeley, studying social and environmental sciences. Her writing on science, health and the environment has also appeared in the Nation, the Guardian, Atmos magazine and Teen Vogue.