Dipylidium caninum, also called the cucumber tapeworm or the double-pore tapeworm, is a cyclophyllid cestode that infects organisms afflicted with fleas, including canids, felids, and pet-owners, especially children. Adult worms are about 18 inches long. Eggs (or “egg clusters” or “egg balls”) are passed in the host's feces and ingested by fleas, which are in turn ingested by another mammal after the tapeworm larvae partially develop. Examples of fleas that can spread D. caninum include Ctenocephalides canis and Ctenocephalides felis .

As in all members of family Dilepididae , proglottids of the adult have genital pores on both sides (hence the name double-pore tapeworm). Each side has a set of male and female reproductive organs. The scolex has a rostellum with four rows of hooks, along with the four suckers that all cyclophyllid cestodes have. In cats, sometimes proglottids are visible hanging out of a cat's anus.

Inside fleas, eggs hatch and form oncosphere larvae that move through the wall of the flea intestine into the body cavity where they become cystocercoid larvae, which are infective to mammal hosts.

In children, infection causes diarrhea and restlessness. As with most tapeworm infections, the drug of choice is niclosomide . The best way to prevent human infection is to treat infected animals and to kill fleas.