Preventing Chafer beetle Larvae Chafer Beetle Larvae: Control with Parasitic Nematodes Chafer Beetle BC11 Large white grubs that feed on grass roots causing damage to lawns & other grassed areas. Secondary damage may be caused by birds pulling up the lawn to feed on the grubs. Control with Parasitic Nematodes for Chafer Grubs (Heterorhabditis sp.): Microscopic transparent worms which feed & multiply inside the larva, not visible with a hand lens. Diluted with water before use & applied when the soil is moist (water if necessary) in July & August. Having trouble with garden pests? These biological control products will ensure that pests stop killing your plants.