Cat Fleas and Dog Fleas

There are "cat" fleas and "dog" fleas, though both species can inhabit other hosts.

Oddly the dog flea is rarely found in the United States; almost all fleas found on dogs in the US are "cat" fleas.

The cat flea (Ctenocephalides felis) is a the most common kind of flea around the world, and its principal host is the domestic cat.  Again, almost all fleas found on dogs in the US are cat fleas.

The dog flea (Ctenocephalides canis) can live on wide variety of mammals, including both the domestic dog and cat, and at times humans.  It closely resembles the cat flea, Ctenocephalides felis, which can live on an even wider range of animals, but is particularly problematic in that it can spread Dipylidium caninum, the flea tapeworm. Dog fleas are more common in Europe, Africa, and Asia than they are in the US

One country with very few fleas on their dogs:  Korea. Koreans typically take off their shoes when they enter a house, and their homes are heated with an underfloor heating system with laminate (no carpet) on top. This result is a low-humidity conditions near the floor, which tends to kill off fleas.