Adults range from 3mm - 6mm in length and usually consist of a scolex, and three proglottids. The third (terminal) proglottid is gravid, and is longer than wide, as can be seen here. The scolex contains four suckers and a rostellum with 25-50 hooks. Large numbers of adult tapeworms may be found in the small intestines of dogs which are infected by eating the remnants of sheep, cattle or other animals containing hydatid cysts. As dogs and other canids are the only definitive hosts for Echinococcus, adult worms are not expected to be found in the human host. Humans are only infected by the larvae after ingestion of eggs from food, water or fomites contaminated with dog feces. Upon ingestion of the eggs by the human host, the oncospheres migrate from the intestinal lumen to other body sites where they develop into hydatid cysts. These cysts can be found in any part of the body, but are most common in the liver, lung and central nervous system. Image courtesy of: CDC/Dr. Peter M. Schantz.