Our guide to British invertebrates
About one-sixteenth of an inch long
Incredibly, there are more than 2,000 species of this wingless, blood-sucking insect in the world, many of which are tied to a specific host, such as cats and dogs. The best jumpers in the animal kingdom—a human would have to jump 295ft long and 160ft high to match their agility—fleas breed prolifically and quickly cause infestations. Indeed, the fleas from the black rat are believed to be responsible for spreading the bubonic plague (Black Death).