Nematodes are microscopic worms that live in the soil. They sometimes hunt for bacteria and feed off small organic matter but primarily live as parasites, entering into other animals and feeding off them. Some nematodes benefit plants and gardeners by killing harmful pests while other nematodes can damage plants themselves. Other nematodes infect humans and can weaken or kill them, depending on the extent of the infection.

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Beneficial Nematodes

The insect-killing parasitic nematodes enter another organism and spend part of their life cycles growing inside that organism. Lawn owners sometimes use parasitic nematodes to attack grubs that can destroy lawns. They feed off the grubs and will not otherwise harm the lawn. Lawn owners really have no choice but to use organic techniques for killing grubs, such as parasitic nematodes, because there are no non-organic alternatives.

Plant Nematodes

Some nematodes enter into plants instead of insects. Root knots live in hot climates and attack the roots of plants. Sting nematodes thrive in sandy areas and wreak havoc on cotton, soybeans and potatoes. These nematodes live in water and enter the plant when the plant absorbs water infected with nematodes. Some of these nematodes move from plant root to plant root, while other nematodes remain in one plant.

Roundworms

Some nematodes infect humans. One kind of harmful infectious nematode is the roundworm, which can infect humans. They live inside the small intestines and mostly eat the food traveling down the small intestines. However, they can also bite the intestine lining and drink blood. Those with roundworms often do not even know that they have them.

Some larvae can migrate to the lungs where they can cause health problems. They can also cause digestive disorders in larger numbers, contribute to malnutrition and even cause intestinal blockages that require surgical removal.

Hookworms

Hookworms are nematodes that can also infect human intestines. Hookworms infect more humans than most other nematodes. These parasites remain in soil where they feed on bacteria and decaying matter. When an animal walks on the soil, the hookworms enter through its feet and travel through the body until they reach the intestines after a long journey via the heart and lungs.

These hookworms attach to the intestinal walls and gain sustenance by drinking blood in the intestines. These hookworms can draw a lot of blood and cause anemia and a decline in iron. In children this can lead to mental retardation and chronic fatigue.