The physical differences between dog and cat fleas can only be seen under a microscope. However, the main difference is that dog fleas can only feed on dogs, while cat fleas can feed on both cats and dogs.
Dog fleas are extremely rare in the United States and are mostly found in Europe. In the United States, nearly 95 percent of all cases in which a dog is infested with fleas involve cat fleas. While cat fleas have adapted to living on both dog and cat blood, dog fleas have not. Although dog fleas might live in the fur of cats for several days, they do not bite the cats. Instead, they ride on the cats until they can find a canine to feed on.
Cat fleas can develop at an alarming rate. They produce eggs that hatch into larvae. Since adult cat fleas can lay up to 20 eggs per day, it's easy to see how quickly these fleas can multiply. Dog fleas can spread just as quickly, and most produce around 4,000 eggs in one life cycle.
The symptoms of both cat and dog fleas are the same: red skin, excessive itching and secondary infections. In some cases, the animal infested with fleas develops flea allergy dermatitis.