What you should know.
A grubs final state is the Japanese beetle. It was first discovered in the United States in 1916 and thrives in all of the Northern United States.
The grub begins its life feeding on the roots and underground stems of turfgrass (your lawn). They are extremely destructive long before the human eye sees the actual damage.
Damage you would see in late summer or early fall is dead/brown grass patches. (You typically can roll these patches back like carpet. You may even see these unsightly pests hanging out.) If you find 5-10 grubs in a 1'x1' area you don't need to worry. But if you are finding 10 or more grub in a small area, you need to be concerned.
You may experience a spongy feel when walking on damaged turf.
After the grub damage your lawn and emerge as Japanese Beetles they begin to feed on your plants, flowers and foliage of trees in the area.
These grubs are a food source for skunks, and greater damage can occur as the skunks dig up your lawn to eat the grub.