We will cover the six major species of intestinal nematodes found in humans. Others exist but are mostly zoonotic (mainly found in other animals in which the human is an incidental or accidental host), or are very regional or rare. Two of these that are worth a mention are Trichostrongylus spp. whose eggs resemble but are somewhat larger than hookworm eggs, and Capillaria philippinensis whose eggs have two flattened polar prominences and may vaguely resemble Trichuris eggs.
Table 6 indicates whether the ingested parasite will migrate out of the intestine to the lungs, and be swallowed to return to the intestine before it matures into an adult. Also, it indicates whether the organism must spend at least part of its life cycle in the soil before it is infective. All of the parasites listed eventually live as adult worms in the human intestine.
Table 6. Nematodes and their Life Cycles.
| Migratory Phase in Humans before becoming an Adult? | Soil Requirement | Method of Diagnosis |
| Ascaris lumbricoides | Yes | Yes | Eggs in feces |
| Enterobius vermicularis ("pinworm") | No | No | Eggs in perianal folds (scotch tape prep) |
| "Hookworm" (Necator americanus and Ancylostoma duodenale) | Yes | Yes | Eggs in feces |
| Strongyloides stercoralis | Possibly | Yes | Larvae in feces |
| Trichuris trichiura ("whipworm") | No | Yes | Eggs in feces |
