Fleas do indeed have a remarkable leaping ability, and in fact, they have the second largest jumping ability in the animal kingdom. Only a single species of frog can jump farther than the flea, when measured against body size.
Fleas can launch themselves approximately 12 inches horizontally and 7 inches vertically with one jump. They have extraordinarily long hind legs which give them superior leverage and the ability to catapult themselves long distances.
The flea puts this great jumping ability to good use. It developed the skill through evolution because of the need to launch itself onto the body of a suitable host when that animal moves through its environment.
The flea can detect a host through minute vibrations in the air and ground caused by movement, as well as by increased levels of carbon dioxide in the air due to the animals respiration.