How Many Fleas Are in the World?

There is no precise figure for how many fleas are in the world. Nevertheless, fleas are ubiquitous. They are also responsible for various diseases, such as a disease called bubonic plague. This deadly disease is spread by fleas which bite infected rodents. Major plague outbreaks in history include the Black Death, which occurred about 1350, and the Plague of Justinian, which occurred about 540.

Fleas can grow up to 3 millimeters (1/8 inch) in length. They live as external parasites and survive by sucking blood from their hosts. Adult fleas lack wings, claws, or a skeleton, and instead have modified mouthparts designed to pierce the skin of their hosts. Some flea species even have barbed stylets to assist them in penetrating the host’s skin.

Adult female fleas lay eggs in the host after a blood meal. They can lay up to hundreds of eggs in their lifetime. The eggs are pearl white, oval, and non-sticky and measure 0.1 to 0.5 millimeters in length. The female flea lays eggs while the host is alive, but after the host is dead, the eggs fall off and land in the host’s sleeping area.

Humans, animals, and birds are the most common hosts for fleas, but there are other species of mammals in the world that are not affected. Among the most commonly infected mammals are rodents, which live in holes and often have less than one flea per host. In fact, a single flea can live for up to nine months in freezing temperatures.