Fleas jump 18 centimetres up yet never grew wings
Fleas—order Siphonaptera—number about 2,500 species of tiny flightless insects that drink blood from mammal and bird hosts. Genetics nest them among parasitic scorpionflies. The oriental rat flea Xenopsylla cheopis spreads Yersinia pestis, the bubonic plague bacterium, via bitten rodents such as black rats.
Adults run 1.5 to 3.3 millimetres, often reddish-brown like the cat flea, and pierce skin with a stylet. They have no compound eyes, only simple single-lens eyespots or none at all, and hard plates bristling with backward spines help them hold on as they slip through fur and feathers. A flea can jump 18 centimetres up and 33 across, roughly 60 times its length in height, making it the second-best jumper relative to size after the froghopper.
Eggs hatch into pale, eyeless, bristly larvae that chew organic debris, especially adult droppings full of dried blood; in lab tests only 12 percent of larvae reared on blood alone matured. After three stages they spin silk cocoons, and metamorphosis can take four days or wait much longer until a host appears. Newly emerged adults must feed on blood before they can breed. Females may lay 5,000 or more eggs, though adults usually live only two or three months. Rabbit fleas even time their breeding by sensing stress hormones in a pregnant doe’s blood, then move onto the newborn kits.
Linnaeus lumped fleas with spiders and woodlice in his wingless Aptera before Latreille reorganised insects in 1810. A 2020 genetic study placed them inside the scorpionflies, closest to Nannochoristidae. Large wingless stem fleas with sucking mouthparts are known from Middle Jurassic to Early Cretaceous rocks in China and Russia.
The oriental rat flea carries plague bacteria from black rats to people, fuelling the Plague of Justinian around 540 and the Black Death around 1350. Charlie Chaplin even began an unfinished 1919 film about fleas, The Professor.
Source: Flea
