A dog or cat may swallow a flea while self-grooming. Once the flea is digested by the dog or cat, the larval tapeworm is able to develop into an adult tapeworm. The adult tapeworm is made up of many small segments, called proglottids, each about the size of a grain of rice.

What kind of worms come from fleas?

"Fleas are the intermediate host for the tapeworm, Dipylidium caninum." Consequently, tapeworms are more common in environments that are heavily infested with fleas. It is recommended to treat your cat for fleas if tapeworms are noted, and use flea control to prevent future flea infestations and tapeworm infections.

Why do fleas have worms?

In pets with flea infestations, the larval fleas hatching in the area consume organic debris, flea dirt (digested blood shed by adult fleas–it looks like pepper) and any tapeworm eggs. The tapeworm egg proceeds to develop inside the flea and by the time the flea is an adult, the tapeworm can infect mammals.