Grubs that you see in the lawn are the larvae of Japanese beetles, June beetles, and chafers. These grubs are C-shaped, off-white in color with a dark head. They eat the roots of grass, causing irregularly shaped patches of wilted, dead, or dying grass in April and May, and again in August to mid-October, with a serious infestation, the turf can be lifted up from the soil and rolled back like a carpet. If the damage to the grass is not too severe, the grass will recover with normal watering and fertilizing. Lawns that are heavily damaged by grubs will have a yellowish tinge and will feel spongy when walked on.
In small populations, grubs do not represent a problem to a healthy lawn. It is normal for all lawns to have some grubs present. Four to six grubs per square foot of turf probably won't cause any visible damage in a healthy lawn. However, when a lawn begins to have more than six grubs per square foot of lawn, this would be considered a grub problem. To check the size of a grub population in your lawn, dig out a square foot of grass and turn it over to examine the roots. Count the visible grubs. If you have more than six visible grubs, you should consider applying a grub control product. Ten or more grubs per square foot will likely cause damage, especially if the lawn is otherwise stressed.
If animals such as skunks, raccoons, birds, and moles are digging up the turf to feed on the grubs, consider treating your lawn. The grubs can be stressful enough on your lawn. Digging animals can reak havok. It will be almost impossible to get rid of the animals, with an abundant supply of grubs, especially if they have little ones to feed.