Cat fleas, for example, turn up on cats, dogs, rats, squirrels, rabbits, chickens, and humans. We have special springy material in our legs that helps us take off faster than any other animal. Good thing we're such good jumpers. We can't fly. Also, we need to be able to get onto our hosts.
Most hosts are fast movers.
We fleas seem like little pests to you. But in the Middle Ages, we were a very big deal. They died of the bubonic plague , a terrible sickness caused by a bacteria. The bacteria were carried by rat fleas. WHY WE'RE FLAT Adult fleas burrow through fur and feathers.