Grubs are the C-shaped, creamy-white larvae of various adult beetles, such as the Japanese beetle and the June bug. Their presence in a lawn can lead to significant root damage. When the cold season arrives, many homeowners wonder if the winter chill will naturally eliminate these pests from their turf. The answer is generally no, as these resilient insects have evolved strategies to survive deep freezes and reemerge in the spring. Understanding how grubs persist through the winter is the first step toward effective management.
Identifying the Pest: The Grub Life Cycle
The grub’s journey begins in the summer when adult female beetles lay their eggs in the soil, often preferring moist, healthy turf. These eggs typically hatch within a couple of weeks during late summer, giving rise to the first-stage larvae. The newly hatched grubs immediately begin to feed on grass roots, causing initial, often unnoticed, damage to the lawn.
The larvae grow quickly, molting into second and then third developmental stages, known as instars, throughout the fall. The third-instar larva causes the most severe damage before cold weather arrives and prepares to overwinter. As temperatures drop, the grubs enter a period of inactivity before transitioning to the pupal stage. The entire life cycle, from egg to adult beetle, generally spans about one year for most common species.
Surviving the Deep Freeze: How Grubs Handle Winter
Grubs do not die when the ground freezes because they employ behavioral and physiological mechanisms to endure low temperatures.
Behavioral Adaptation: Burrowing
As the soil temperature decreases in late autumn, the larvae instinctively migrate downward in the soil profile. This movement is an adaptation to reach a zone below the frost line where the temperature remains stable and above freezing.
Physiological Adaptation: Diapause and Cryoprotectants
The typical depth they burrow to is often between four to eight inches, depending on the climate and soil type. Once settled, they enter a state of suspended development called diapause. This dormancy is characterized by a dramatic reduction in metabolic rate, cessation of feeding, and minimal energy expenditure.
The physiological mechanism preventing cellular damage is the production of cryoprotectant compounds. These natural antifreezes, often sugars or alcohols, accumulate in the grub’s body tissues. These compounds lower the freezing point of the insect’s internal fluids, allowing them to tolerate temperatures near freezing without forming ice crystals inside their cells.
This combination ensures that a high percentage of the grub population successfully survives the coldest months. By remaining in diapause, they wait until rising soil temperatures signal the time to resume development and feeding activities.
When Grubs Emerge and Treatment Considerations
The overwintered grubs begin to ascend in the soil profile in the early spring as the ground thaws. They move back into the root zone to feed for a short period before they pupate into adult beetles. This brief spring feeding can cause additional damage, especially to turf weakened by the previous fall’s feeding.
The most effective window for intervention is typically late summer or early fall when the grubs have recently hatched and are small. At this time, the young larvae are actively feeding near the surface, making them vulnerable to curative applications. Applying treatments in the spring is less effective because the grubs are larger and will soon stop feeding to pupate. Preventative treatments are applied in early summer to kill the new generation just as they hatch. Treating the soil when grubs are deep and dormant in the winter is not an effective use of control measures.