Much-maligned black rats and their fleas have long been blamed for spreading the Black Death that claimed millions of lives in Europe over the course of a few hundred years, but scientists now have a new critter they think was at fault. By studying tree rings to learn about precise climate fluctuations during the multiple epidemics from 1347 into the 1700s, a team out of the University of Oslo is reporting in the Proceedings of the National Academy of Sciences that giant gerbils in Asia were the more likely culprit. The working theory is that wet springs followed by warm summers in Asia prompted gerbil populations to soar, and that within a few years plague bacteria would show up in harbor cities in Europe, sweeping the continent from there. "If we're right, we'll have to rewrite that part of history," a researcher tells the BBC.
"Suddenly we could sort out a problem," the researcher continues. "Why did we have these waves of plagues in Europe? We originally thought it was due to rats and climatic changes in Europe, but now we know it goes back to Central Asia." Next up: sequencing plague bacteria from skeletons across Europe. If there's considerable genetic variation in the disease, this will support the theory that new strains kept arriving from Asia, as opposed to persisting in rat reservoirs in Europe. Though not what it once was, hundreds of cases of the plague are still reported annually, with 126 deaths in 2013, reports the World Health Organization. (Check out what some researchers call the plague's silver lining.)