Flee from the flea

In almost all cases, it will be cat fleas (C. felis) that infests dogs and cats. The second most common species would be dog fleas (C. canis). The human flea (P. irritans) and sticktight flea (E. gallinacea) are also possible candidates, but they are much more rare on cats and dogs.

More info here: Are cat and dog fleas the same?