Pork tapeworm. Coloured scanning electron micrograph (SEM) of the head of a pork tapeworm (Taenia solium), showing the hooks it uses to cling to its host. Tapeworms are parasitic flatworms that live in the digestive tract of their vertebrate host. T. solium infects pigs and humans in Asia, Africa, South America, parts of Southern Europe and pockets of North America. In the larval stage, it causes cysticercosis, which is a major cause of seizures in humans. Magnification: x60, when printed 10 centimetres wide.