Rat fleas (Xenopsylla cheopis) are blood-sucking parasites. They are external parasites that primarily host on rats like Norway rats or roof rats. They are known to have originated in Europe but can now be found in temperate environments all over the world. Although the rat flea hosts on rats, rat fleas will also feed on the blood of other mammals, including humans.
Rats are known to carry diseases and many people assume that rats are the main vector for transmitting diseases to people. However, fleas are problematic vectors for transmitting diseases. A rat flea will host on a rat that is carrying a disease. They will then become carriers for the bacteria and then the hungry flea will bite a human and regurgitate the bacteria into a new host. The Oriental Rat Flea is a known vector for the bubonic plague, also known as the Black Death that overtook Europe during the Middle Ages.
Rat fleas are flat insects meaning they are compressed from side to side. Unlike the common cat flea or dog flea, the rat flea does not have a genal comb on its head. They are brownish in color and can grow up to 6mm but be as small as 1.2mm long.