Captive-raising monarchs in cages also puts the butterflies at risk. The OE parasite can reach very high levels in indoor butterfly houses. And captive-raised butterflies often are too stunted to migrate, probably because they are weakened by heavy parasitic infections and questionable genetics.

The monarch butterfly population continues to shrink due to factors such as climate change. People working to help the species say proposed federal protections could boost existing efforts.

Federal officials have proposed giving a rare Nevada butterfly endangered species status.The U.S. Fish and Wildlife Service said Tuesday that it was opening a p