Tapeworms differ in appearance from species to species but they all share certain characteristics. From the head, which is attached to the intestinal wall, grows a flat segmented body. New segments are continually growing from the head, which means that the segment furthest away from the head is the oldest.
By the time the segment reaches the end of the body it is full of eggs; the mature segment separates from the rest of the tapeworm and is passed from the host animal. Each segment is self-sufficient and some can even move independently hence the ability to cause irritation around the anus as it passes from the host. When exposed to air the segment dehydrates and splits open, dispersing eggs into the environment.

All tapeworms require at least one intermediate host; this means that an egg must be ingested by another creature, the intermediate host. Within this animal the tapeworm larvae must undergo a stage of development before entering the final host, by means of the final host eating the intermediate host, and reaching maturity.

The species and number of intermediate hosts differs for each tapeworm but includes fleas, rodents and even man. The immature tapeworm forms a cyst within the intermediate host which can have health implications for the animal, or indeed human. For more information see the section on Potential Health Risks.