Residents of Fort Collins, Colorado, have been startled by unusual rabbits with horn-like, black growths on their faces which have been quickly dubbed Frankenstein Bunnies. While their weird appearance has fueled jokes and horror-movie comparisons, wildlife officials say the rabbits are suffering from a well-known viral infection, not a monstrous mutation.

The Virus Behind the Horror Look

According to Colorado Parks and Wildlife, the cottontail rabbits are infected with Shope papillomavirus, a disease that causes wart-like nodules. In some cases, these growths extend outward like horns or tentacles, creating their unsettling look.

“The growths don’t harm rabbits unless they interfere with their ability to eat or see,” said Kara Van Hoose, spokesperson for CPW. “Once the immune system fights off the virus, the growths will disappear.”

The virus is spread primarily by fleas and ticks and is most active in the summer months. Importantly, PetMD notes it poses no risk to humans or pets.

From Myth to Modern Science

While these sightings might seem new, the virus — and the strange rabbit appearances it causes — have a long history.

Shope papillomavirus was first identified in the 1930s by Dr. Richard E. Shope of The Rockefeller University. His work helped scientists understand links between viruses and cancer, such as the human papillomavirus that causes cervical cancer.

The condition also may have inspired the legendary North American jackalope — a mythical rabbit with antlers. As USA Today points out, folklore about horned rabbits predates the modern understanding of the disease by centuries.

Sightings and Viral Photos of Frankenstein Bunnies

The latest attention began when Fort Collins residents started posting photos of the rabbits online. Some images show black, tentacle-like protrusions that seem almost fictional. Social media nicknames have ranged from “Frankenstein bunnies” to “demon rabbits” and “zombie rabbits.”

Van Hoose says sightings are “not uncommon” in Colorado this time of year:

“We get calls every summer about rabbits like this. It’s just that social media amplifies it now.”

What Happens to Infected Rabbits?

In most cases, infected rabbits recover naturally once their immune systems eliminate the virus. However, if growths develop on the mouth or eyes, they can prevent eating and lead to malnutrition or secondary infections. In rare cases, cancer may develop if the virus persists.

For now, wildlife experts recommend leaving the rabbits alone and avoiding direct contact, as handling can stress them and further compromise their health.