The growths are most likely caused by a summertime virus common in some U.S. states, but wildlife officials say there is no risk of transmission to humans or other animals.

Rumors spread online that rabbits infected with a virus that creates a tentacle-like growth on their faces were "invading" the U.S.

According to Colorado Parks and Wildlife's (CPW) website, the black growths on the rabbits' heads are due to a grimmer, more reality-based reason — a viral infection called the cottontail rabbit papillomavirus.