Nemasys Leather Jacket Killer, 100m²Leatherjackets are the soil dwelling larvae of crane flies (also known as daddy long legs) that eat grass roots and can often be the cause of yellowing patches, thinning grass or areas of grass that lift. These microscopic nematodes (Steinernema feltiae) actively seek out and infect leatherjackets in the soil, stopping the damage at its root.