Insect parasitic nematodes are beneficial nematodes that attack the larval stages of soil-dwelling pests, leaving the plants alone. The parasitic nematodes enter their prey through body openings and release bacteria that kills their host within 48 hours. The nematodes can then reproduce inside the pest. Nematodes are recommended for use whenever pest larvae or grubs are present, generally during the spring and fall months. If adult insects are present, their eggs will be hatching soon. As a treatment for Japanese Beetles, parasitic nematodes take effect more quickly than Milky Spore, but annual re-applications are required.

Keep in mind, more than one application may be necessary. Steinernema carpocapsae are best suited to cooler climates, and are most effective against mobile pests such as termites, fleas, webworms, sod webworm and more. Steinernema feltiae are similar to Steinernema carpocapsae except they are best suited to warmer climates. Heterohabditis bacteriophora are adapted to all climates, and are most effective against sedentary pests, such as grubs, root weevils, ants, juvenile and queen, termites and more. For the best treatment of ants or termites and for general soil born pests, a combination of nematodes is recommended.