Pulex irritans, or the human flea, is a small bloodsucking insect that can be found on nearly every continent. It was a common nuisance in both rich and poor households during the Middle Ages but was rarely found indoors by 2011. These insects often irritate the skin when they bite human hosts. They also are capable of spreading serious diseases from one person to another.
The human flea is less common than other varieties such as rat fleas or cat fleas. This species often breeds around pigpens. Human fleas mainly prefer pig and human blood, but they also feed on the blood of badgers, foxes, skunks and some other wild mammals.
Pulex irritans fleas are usually between one-sixteenth and one-eighth of an inch long (1.587 to 3.175 mm). They have dark brown or black bodies, with long, spiny legs; short, jointed antennae; flattened sides; and no wings. They move from one place to another by crawling or jumping. A human flea can jump as much as 100 times its body size.
These insects have piercing and sucking mouthparts. Their saw-like mandibles slice into the host's flesh and release an anticoagulant into the skin to keep the blood from clotting as the insect feeds. They then suck blood from the human or animal host. Fleas can live for months or years without feeding when acceptable hosts are unavailable.
Female fleas lay eggs on the bodies of their hosts. The eggs are not barbed or sticky and do not adhere to the host, so they often fall from the animal and into its bedding. The eggs hatch into white, worm-like, legless larvae. Larval human fleas feed on adult fecal matter and organic animal material.
Young fleas shed their exoskeletons three times before entering a pupal stage. They mature inside silken cocoons and exit as adults. The maturation process usually takes three to four weeks, depending upon climate and host availability.
Human flea bites usually leave small, red, itchy marks on hosts when they feed. Some people are more sensitive to flea bites than others. The anticoagulant in human flea saliva might cause severe itching or rash. Scratching the flea bites might lead to secondary infections.
Pulex irritans is capable of spreading the Yersinia pestis bacterium from rats to humans. This bacterium causes bubonic plague, a serious disease that killed approximately 200 million people during the 14th century in a pandemic called the Black Death. Plague outbreaks were still occurring as of 2011, but antibiotics have greatly improved the survival rate of infected patients.