They return to the soil in the late afternoon or evening to spend the night. Beetles also remain in the soil on cold wet days. Eggs measure about 1.5 mm in diameter and are laid in the soil in July and August. Beetles generally lay their eggs in short grasses. Larvae begin to hatch in late July and go through three molts before fall.
Grubs begin to move downward during the first freezing air temperatures in the fall for hibernation.
Grubs move up again during April and May to feed and reach maturity. Life cycle of Japanese Beetle. Birds and mammals considerably reduce Japanese beetle grub populations just as they do those of other scarabaeid grubs but may also cause considerable turfgrass damage in the process of digging for their quarry. Starlings, grackles, robins and other birds feed on large numbers of grubs especially during early spring and fall. When crows dig for grubs, they can cause considerable damage to the weakened turf.