Colorado Parks and Wildlife: Scary-looking rabbits were hopping around Fort Collins. These weren’t your standard cute, fluffy bunnies; they had horn-like growths protruding from their faces and bodies.

Viral photos have inspired a fluffle of unflattering nicknames, including "Frankenstein bunnies," "demon rabbits" and "zombie rabbits."

The beleaguered bunnies are infected with cottontail rabbit papilloma virus – also called Shope papilloma virus – which is spread by biting insects, such as mosquitoes and ticks, and causes black nodules on the skin, usually on the head, which can become elongated and may come to resemble horns.