33. Rats and fleas formed a deadly duo that spread the Black Death in 1347, killing 50 million people
The Black Death killed 50 million people in the 14th Century. That’s 60% of Europe’s population! Medieval people thought God’s anger, the movements of planets, or a Jewish conspiracy caused the Black Death. In fact, Black Death (bubonic plague) is a disease caused by Yersinia pestis, a bacterium living on rats. Rats die of bubonic plague in a few days, and the fleas living on them have to find new hosts. Often, the new host isn’t a rat, but humans. Between them, therefore, rats and fleas wiped out millions. The population deficit also changed the medieval social structure forever.
