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Plague is caused by a bacterium called Yersinia pestis. The fleas pick up the germs when they bite infected rats, mice, or squirrels. Rat fleas transmit disease as they feed, squirting saliva or partly digested blood into a human or animal. Like all fleas, the rat flea does not have wings, but its powerful legs allow the pest to jump from place to place. Experts have documented sporadic cases of the plague in modern times, including in Vietnam during the war there in the 1960s and 1970s. Every once in a while, someone in the United States contracts the disease as well. For instance, a young boy in Idaho developed plague in 2018. He received treatment and recovered.

Plague doctors wore bird-like masks because they thought the masks offered them protection from disease. It would not be until the early 1900s that people understood that plague was transmitted by fleas rather than through the air.

Northern Rat Flea

The northern rat flea is one of the most plentiful flea species in the world. It specifically likes to feed on the blood of

Scientific Name: Nosopsyllus fasciatus Range: Native to Europe, but found all around the world Life Span: 4–17 months, depending on climate conditions Danger: Carrier of bacteria that cause plague and tapeworm

rats and mice. The insect is not only a carrier of the bacterium that causes the bubonic plague, but it can also transmit rat tapeworm, which in rare instances can infect humans. The northern rat flea is one of the smallest fleas on the planet, being roughly 3 to 4 millimeters

(.11–.15 inches) in length. Like all fleas, the northern rat flea thrives in hot, humid environments. While they don’t generally infest dogs and cats, as other fleas do, the

Dangerous Bloodsuckers

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