Nematodes are tiny roundworms—so tiny you need a microscope to see them. While some are pests because they eat your plants, others are beneficial because they kill insects —including many pests. These nematodes that kill insects are called entomopathogenic nematodes, or EPNs, for short. They are completely harmless to you and your plants and are most often found in soil. Different EPN species and strains prefer different temperatures, use different strategies for finding the insects they eat, and live at different depths in the soil. Some are better at killing certain insect species than others.