Grubs are the larval stage of a scarab beetle. There are at least ten different species of beetles that produce grubs that damage lawns to varying degrees. About a week ago, I saw the adults of the Masked Chafer, a common beetle in cool season turfgrass areas in the Midwest and Lower Midwest including the Chicago area. They seem to be out a little earlier than normal this year. The beetle that seems to cause the most damage is the Japanese beetle as the adults feed on many trees and flowering plants. The female adult lays her eggs in turf areas, which hatch into lawn damaging grubs. The Japanese beetle adults will start hatching soon and begin feeding. In some southern areas, the adults may already be active.
The grubs act like mini sod cutters as they feed on the roots of the grass plant, starting in mid-July and lasting well into fall. If rain is plentiful, the grass plants can often replace the roots that have been eaten and the damage may go unnoticed. The bigger problem comes from skunks, raccoons, opossums and even birds that tear up a lawn looking for a tasty meal. They damage caused by these animals and birds are often far worse than what the actual grub will cause.
The best defense is to apply a preventative grub control now, before the eggs hatch, to prevent them from becoming a problem. The insect control material has to be watered in well to move it into the soil where the insect can come in contact with it. If you have had problems with grubs in the past, now is the time to prevent damage later this year.