A Galapagos Finch. (Credit: Ryan M. Bolton/Shutterstock)

Nearly 200 years ago Charles Darwin voyaged to the Galapagos islands and began to formulate his theory of evolution — largely thanks to his observations of how finches’ beaks varied in shape from island to island. But now, the finches’ famous beaks might be in trouble, thanks to a small, blood-sucking visitor.

An invasive insect, called Philornis downsi, is finding a home in the nests of almost every species of ground bird on the