‘Flea’ is the common name for insects of the order Siphonaptera, which are wingless insects with mouthparts adapted for piercing skin and sucking blood. Fleas are external parasites, living on the blood of mammals (including humans) and birds. In the past, it was most commonly thought that fleas had evolved from the flies (Diptera), based on similarities of the larvae. Now it is more certain that they are descendants of the snow scorpion-flies, family Boreidae, which are also flightless. There are around 2000 species of fleas known worldwide and the number of local species is yet to be determined.
Their legs are long, the hind pair well adapted for jumping vertically up to 18 cm and horizontally up to 33 cm on average. This is around 200 times their own body length, making the flea one of the best jumpers of all known animals (in comparison to body size), second only to the froghopper. Their bodies are laterally compressed, permitting easy movement through the hairs or feathers on the host’s body (or in the case of humans, under clothing). The flea body is hard, polished, and covered with many hairs and short spines directed backwards, which also assist its movements on the host. The tough body is able to withstand great pressure, likely an adaptation to survive attempts of eliminating them, such as mashing and scratching. Even hard squeezing between the fingers is normally insufficient to kill a flea.
Once the flea reaches adulthood, its primary goal is to find blood as it is the only diet for adult fleas. Adult fleas only have around a week to find food once they emerge, though they can withstand between two months and a year between meals. A flea population is unevenly distributed, with 50 percent eggs, 35 percent larvae, 10 percent pupae, and 5 percent adults. Their total life cycle can take as little as two weeks, but may be lengthened to many months if conditions are favourable. Female fleas can lay 500 or more eggs throughout their lives. Adaptations can be clearly observed in Rabbit Fleas (Spilopsyllus cuniculi) Bergħud tal-Fniek. Fleas attack a wide variety of warm-blooded vertebrates including dogs, cats, mice, chickens, rabbits, squirrels, rats, ferrets, and humans. The most common species include Cat Flea (Ctenocephalides felis) Bergħud tal-Qtates. The primary host of this species is the domestic cat, but this is also the primary flea which infests dogs in most of the world. The cat flea can also maintain its life cycle on rabbits, rodents, ruminants and humans, but a population of cat fleas cannot be sustained by these aberrant hosts. The Dog Flea (Ctenocephalides canis) Bergħud tal-Klieb, is very similar in habit to the cat flea but it is more commonly found in Europe. On the other hand, the Human Flea (Pulex irritans) Bergħud tal-Bniedem, is a cosmopolitan flea species that has, in spite of the common name, a wide host spectrum. Besides the problems posed by the creature itself, fleas can also act as a vector for disease. A very famous example is the Black Death, which killed millions of people in Europe during the middle ages, because of a flea species which was common on Black Rats, which acted as a vector for the bacterium Yersinia pestis.