However, before toilets and running water were ubiquitous, everyone was often exposed to intestinal worms. With the exception of a few pinworms in certain youngsters, individuals in the industrialized world have lost practically all of their worms, thanks in part to modern plumbing. In fact, before the advent of sanitation practices, almost everyone had some form of intestinal worm. While many people were infected by parasitic worms, a small but significant minority was also covered in skin-colored or white worms. These were called "tapeworms" because they looked like strings of spaghetti stuck into the bone when seen under the microscope. The human tapeworm is actually a group of related parasites that can grow quite large; one species, Hymenolepis diminuta, can be as long as 15 inches (38 cm). Other common names for human tapeworm include encysted worm, encysted hookworm, encysted roundworm, encysted segmenterian, and encysted tapeworm. People became aware of the presence of intestinal worms about 400 years ago, but since then medical research has shown that most people throughout history have been infected with at least one type of parasite. The two main groups of intestinal worms are the nematodes and the cestodes. Nematodes include rootworms, rattlesnake worms, hookworms, pinworms, and threadworms.