Nematodes, also called “roundworms,” are a group of tiny animals found just about everywhere. Some live in the soil, some in the water, and some even live as parasites inside other animals.
Mononchus is the name of a group of nematodes. Some Mononchus species live in the water, and some on land. This kind of nematode is not a parasite.
Mononchus nematodes are predatory, meaning they feed on other animals, including other nematodes.
You can find Mononchus in damp soil, sand or gravel on the shore of a water source, or on the bottom of a lake, pond, stream, river, or marsh.
Nematodes are transparent, meaning you can see through them. If they have color, you’re just seeing what they ate.
Mononchus nematodes are only about a millimeter long, so you need a microscope to see one well. Females are a little bigger than males.
As they move through soil, Mononchus looks for food. Young Mononchus eat microscopic creatures, such as protists (Amoeba, Paramecium, Euglena, etc.). Adult nematodes attack protists as well as Rotifers, Water Bears, Aquatic Worms, and other nematodes. Mononchus will even eat each other!
The mouth of a Mononchus has a “tooth” that it uses to grab prey. Then the nematode swallows it whole.
This information is adapted from http://www.fcps.edu/islandcreekes/ecology/predatory_nematode.htm which no longer is available on the web.