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.

A rare tiny butterfly found only in a remote stretch of Northern Nevada will soon gain federal protections under the Endangered Species Act. The U.S. Fish and Wildlife Service announced Tuesday that the bleached sandhill skipper,