Several important feeding groups of nematodes commonly occur in most soils. The nematode feeding groups are called trophic groups by some authors. These are the plant parasites, which are relatively well known. This group includes many members of the order Tylenchida, as well as a few genera in the orders Aphelenchida and Dorylaimida. The mouthpart is a needlelike stylet which is used to puncture cells during feeding.
Ectoparasites remain in the soil and feed at the root surface.
Endoparasites enter roots and can live and feed within the root. In the herbivore, the mouthpart is modified into a stylet for puncturing plant cells. In the bacterivore, the mouth or stoma is a hollow tube. Many kinds of free-living nematodes feed only on bacteria, which are always extremely abundant in soil. This group includes many members of the order Rhabditida as well as several other orders which are encountered less often.