Understanding what Nematodes are

Biologist E. O. Wilson stated that it “was a nematode world” and how right he was.  These simple roundworms are the largest family of multicellular animals on earth.  Just one gram of soil may contain just over 100 nematodes.  It is unknown exactly how many species of nematodes exist, but a conservative estimate puts it at 20,000.  Species range in size from 0.3 millimeters to the 8 meter long Placentonema gigantisma, a parasite of sperm whales.

Body Structure

The University of Nebraska-Lincoln’s Department of Nematology describes nematodes as a “tube within a tube.”  Their worm-like bodies consist mainly of their tube-like gastrointestinal tract, called the alimentary canal.  Most species lack coloring or other identifiable features.

Since many nematode species look alike, even a nematologist can have trouble identifying particular species.  But each nematode species tend to have a narrow range of prey plants or animals.  Looking at what animal, insect or plant that a nematode is found in can help scientists identify species.


Although nematode bodies may be simple, their love lives are anything but.  Some species need to be incubated in the body of a completely separate animal species before they can reproduce.  For example, let’s look at Myrmeconema neotropicum, a species only discovered in 2008.  It lives on one ant species, Cephalotes atratus, found in the South American rainforest.  Inside of the ant, the immature pupae become adults and reproduce.

The adults move to the ant’s abdomen and lay their eggs.  This causes the abdomen to swell up like a red berry.  The ants are easily spotted by berry-eating birds and plucked off.  That’s the end of the ant, but not the nematodes.  Inside of the bird’s body, the eggs hatch and harmlessly move through the bird’s digestive system, to be neatly deposited in the bird’s droppings.  These droppings are then eaten by the ant. Guano happens to be the favorite food of Cephalotes atratus.  This one species needs not just one but two non-nematode species in order to continue its life cycle.

Beneficial Nematodes

Depending on the species, nematodes can be deadly predators.  But some nematode species prey on creatures that humans consider pests.  These are called beneficial nematodes.  They are planted in moist soil as close to insect nests as possible.  The nematodes need to tunnel through the dirt and hope they come into contact with a prey species before they die of starvation.

Beneficial neamtodes have been used in combination with other organic methods to eliminate pests such as slugs, snails, white grubs, banana moths, fungus gnats, crane flies, armyworms, pillbugs, sweet potato weevil and mole crickets.  They are advertised to kill other serious pests like cat fleas and subterranean termites, but they are not as reliable as other pest control methods.