Grubs are the larval stage of various beetles, such as Japanese beetles, June bugs, and chafers. These soft, C-shaped insects spend the vast majority of their existence hidden beneath the lawn. Understanding exactly where these pests live and feed at different times of the year is crucial for effective control and turfgrass health. Their habitat is a dynamic subterranean environment that changes dramatically with the seasons and stages of their life cycle.
The Primary Feeding Zone
The most damaging location for a grub infestation is the primary feeding zone, which exists just beneath the soil surface. This zone is concentrated in the top one to four inches of soil, where the dense network of grass roots provides their main food source. Grubs, particularly in their later larval stages, are voracious, severing the roots that anchor the turf. Their peak feeding activity occurs in late summer and early fall, when the grubs have hatched and grown large enough to cause significant damage. By consuming the root system in this shallow layer, grubs effectively detach the turf from the soil, leading to the first visible signs of lawn distress.
Seasonal Movement and Soil Depth
The location of grubs changes dramatically in response to ground temperature. As the soil temperature drops below 50 degrees Fahrenheit in late fall, the grubs begin a downward migration to survive the cold. They burrow deeper into the soil, often reaching depths of six to twelve inches, positioning themselves beneath the frost line. During this overwintering period, the grubs enter a state of semi-dormancy, ceasing their feeding activity entirely. When the soil warms again in early spring, the grubs reverse their movement and travel back up toward the root zone to feed briefly before they transition into the next stage of their life cycle.
Visual Indicators of Grub Presence
The first indication of a grub habitat is not the sight of the insects themselves but the consequences of their feeding. The most characteristic sign is the appearance of irregular, wilting brown patches in the lawn that do not respond to watering. This discolored turf looks like it is suffering from drought stress, but the damage is caused by the roots being completely severed. A simple test is to attempt to pull up the turf in the damaged area; if grubs are present, the grass will roll back easily like a loose carpet because the root system is no longer intact. Another strong indicator is the increased presence of predators, such as skunks, raccoons, and birds, who actively dig small, distinct holes in the lawn to feed on the grubs.
The Pupation Chamber
The final temporary habitat is the pupation chamber, which marks the end of the larval stage. After spring feeding, mature grubs construct a protective enclosure in the soil. This chamber is typically located four to six inches deep, slightly below the main feeding zone, where soil conditions are stable. Inside this small, oval chamber, the grub transforms into a pupa, a non-feeding, stationary stage lasting several weeks. Once the transformation into the adult beetle form is complete, the beetle emerges and tunnels out of the soil to begin the cycle anew by laying eggs in the summer.