A variety of different intestinal worms afflict humans. Each type looks slightly different from the others. According to Scientific American, pinworms are the most common parasites that afflict people living in temperate areas. The adult female pinworm is very thin, tapered at both ends and about the length of a staple. At night, the females exit through the rectum of their host, and deposit eggs near their host’s anus.
While most worms that sicken humans have the same general shape, they differ in other ways, such as their color or opacity. For example, as pictured on Scientific American’s website, Trichinella larvae are largely transparent, while whipworms are only partially transparent. Whipworms are very long, thin and strongly tapered at one end, which gives them the appearance of a cow whip, and led to their common name.
Roundworms are the most common intestinal parasite in the world, afflicting nearly 1.5 billion people living in the tropics annually. Roundworms grow quite large, and sometimes exceed three feet in length, according to the University of Maryland Medical Center. According to ParasitesInHumans.org, tapeworms are flat, segmented worms with hooked heads. In rare circumstances, the worms can exceed 30 feet in length. Tapeworms cause intestinal distress in humans and must be treated with drugs.