Plague Fleas Vomited Infectious Blood

Fleas acquired Yersinia pestis by feeding on infected rats or other rodents. The bacteria multiplied within each flea, creating a plug that blocked its stomach, leaving it starving no matter how often it ate. The hungry flea would bite a new host again and again, spitting the blood-laced bacteria into each new wound, passing on the infection, until it finally died of starvation. This cycle of transmission led to large epidemics such as the Black Death in the 14th century.

Previous Fact Next Fact