Nematodes (also called roundworms) are a diverse group of organisms that live in a broad range of habitats. Scientifically speaking, they are in the animal kingdom and Nematoida class. About 28,000 species have been identified, of which slightly more than half are known to be parasitic. Anatomically, nematodes are small worms, ranging from a microscopic size to over 1 meter in length. Typically they are most commonly between 0.1 and 2.5 mm in length.
Nematodes can be found in all environments including oceans and lakes, polar regions and tropics, as well as deserts and ocean trenches. From a gardening perspective, there are both beneficial and harmful nematodes, typically classified as predatory (beneficial) and pest nematodes.
Beneficial nematodes feed on soil dwelling insects typically by entering their body, injecting them with some lethal bacteria, and feeding from the inside, killing the host within a day or two. Beneficial nematodes are often purchased in a powder form and are easily applied by mixing the powder in a watering can and applying diectly to the garden in either the morning or evening.
In Canada, you can purchase beneficial nematodes from Natural Insect Control.
Cover Image by Scot Nelson, used under its Creative Commons license.