Grub worms feed on the roots of your grass. The damage can be fatal to your turf. Grubs feed on virtually all types of turf grasses. Normally there are not enough of them present in one area of the lawn to show noticeable damage, but heavy damage can occur if 10-15 grubs feed within a small area. Grubs are normally deep in the soil, and come up to feed only certain times of the year.