Animals around the world are on the move. So are their parasites.

Recently, scientists carried out the first large-scale study of what climate change may do to the world’s much-loathed parasites. The team came to a startling conclusion: as many as one in three parasite species may face extinction in the next century.

As global warming raises the planet’s temperature, the researchers found, many species will lose territory in which to survive. Some of their hosts will be lost, too.

“It still absolutely blows me away,” said Colin J. Carlson, lead author of the study and a graduate student at the University of California, Berkeley.

He knows many people may react to the news with a round of applause. “Parasites are obviously a hard sell,” Mr. Carlson said.