Introduction to Soil Nematodes


Common Name: Nematode

Genus: Dictyoptera

  What Is A Nematode?

Nematodes are microscopic, whitish to transparent, unsegmented worms. They occupy almost every conceivable habitat on earth, both aquatic and terrestrial, and are among the most common multi-celled organisms. Nematodes are generally wormlike and cylindrical in shape, often tapering at the head and tail ends; they are sometimes called roundworms or eelworms.

There are thousands of kinds of nematodes, each with their particular feeding behavior. One teaspoon of good soil typically contains about 20 bacteria-eating nematodes, 20 fungi-eating nematodes and a few predatory and plant-eating nematodes.

Nematodes and Mineralization

Arguably, mineralization is the most important thing nematodes do for gardeners.

Nematodes feed on bacteria and fungi and then excrete the nitrogen they assimilated in excess of that required for growth. This increases nutrient availability for other soil organisms. The process is called mineralization.


The body of a nematode is long and narrow, resembling a tiny thread in many cases, and this is the origin of the group's name. The word "nematode" comes from a Greek word "nema" that means thread.

The epidermis (skin) of a nematode is highly unusual; it is not composed of cells like other animals, but instead is a mass of cellular material and nuclei without separate membranes. This epidermis secretes a thick outer cuticle which is both tough and flexible. The cuticle is the closest thing a roundworm has to a skeleton, and in fact the worm uses its cuticle as a support and leverage point for movement.

Long muscles lie just underneath the epidermis. These muscles are all aligned longitudinally along the inside of the body, so the nematode can only bend its body from side to side, not crawl or lift itself.

The head of a nematode has a few tiny sense organs and a mouth opening into a muscular pharynx (throat) where food is pulled in and crushed. This leads into a long simple gut cavity lacking any muscles, and then to an anus near the tip of the body. Food digested in the gut is not distributed by any specialized vascular system, and neither is there a respiratory system for the uptake or distribution of oxygen. Rather, nutrients and waste are distributed in the body cavity, whose contents are regulated by an excretory canal along each side of the body.

Nematodes anatomy graphic

Benefits From Nematodes

  Arguably, mineralization is the most important thing nematodes do for gardeners. Nematodes mineralize nutrients into plant-available forms, provide a food source for other soil organisms

  Nematodes help distribute bacteria and fungi through the soil and along roots by carrying live and dormant microbes on their surfaces and in their digestive systems.

  Nematodes are food for higher level predators, including predatory nematodes, soil micro-arthropods, and soil insects.

  Some consume disease-causing organisms, such as root-feeding nematodes, or prevent their access to roots resulting in disease suppression.

  Nematode Life Cycle

The life cycle of beneficial nematodes consists of six distinct stages: an egg stage, four juvenile stages and the adult stage. The adult spends its life inside the host insect. The third juvenile stage, called a dauer, enters the bodies of insects, usually the soil dwelling larval form. In less than two weeks the nematodes pass through several generations of adults, which literally fill the insect cadaver.

  Predators of Nematodes

Because nematodes often occur in high numbers in soil, it is not surprising that a wide variety of soil organisms exploit nematodes as food, i.e., as sources of carbon, nitrogen, and energy. Those organisms that seek out and consume nematodes are called predators.

Predators of plant-parasitic nematodes include mites, collembola, flatworms, protozoa, and other predatory nematodes.

There are also nematode parasites that have prolonged and specialized interactions with nematodes. Parasites of plant-parasitic nematodes include fungi, bacteria, and mycoplasma-like organisms.

  Picky Eaters

Nematodes are major consumers in the soil. The best way to classify them is by their eating habits. The various kinds of nematodes have developed specialized mouth parts to allow them to attach and get at their particular kind of food.

  Plant-Eating Nematodes

These plant parasites eat plant roots and can create lesions in the root as well as cysts or large bulges, often referred to as 'plant knots.'

  Bacteria-Eating Nematodes

Known as bacterivores, these nematodes eat soil bacteria. Their mouth part is a hollow tube and can consume multitudes of tiny bacteria in a single hour.

  Fungi-Eating Nematodes

Known as fungivores, they have a specialized mouth part with a stylus that can puncture the chitin walls of fungal hyphae.

  Predator-Eating Nematodes

These nematodes feed on protozoa, alga and other small members of the soil such as grubs, weevils, wasps and even snamp invertebrates such as slugs.

  Nematodes and Japanese Beetles

Because grubs are constantly on the move to find over-wintering sites in the soil during September through October, they become easy targets for beneficial nematodes. Nematodes use symbiotic bacteria as weapon to kill Japanese beetle grubs or pupae and as food.

  Gardening With Nematodes:

  Most nematodes species are compatible with pressurized, mist, electrostatic, fan and aerial sprayers. Hose-end sprayers, pump sprayers, and watering cans are effective applicators as well.

  Fertilizers should be avoided roughly 2 weeks prior to and after nematode application, because they may be adversely affected by high nitrogen content.

  Since beneficial nematodes are susceptible to UV radiation, it is recommended to apply them in the evenings.

  Nematodes need a film water for their easy movement in the soil, apply them when there is enough moisture present in the soil. It also recommended applying irrigation after application of nematodes so that irrigation water will wash them from grass blades into soil.

  Repeat applications if the insect is in the soil for a longer period of time.

  Because they leave no residues, application can be made any time before a harvest and there is no re-entry time after application.

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