White grubs are the larval stage of several species of scarab beetles (family Scarabaeidae). These soft-bodied larvae are whitish or cream-colored with a distinct brown head capsule and a characteristic C-shape when found in the soil. The grub stage is known for its destructive feeding behavior, chewing off the roots of turfgrass and other plants just beneath the surface. The grub undergoes complete metamorphosis, transforming into a flying adult beetle.
Specific Beetles That Emerge from White Grubs
The identity of the adult beetle depends entirely on the grub species, with some of the most common varieties being the Japanese beetle, the May or June beetle, and the European chafer.
Japanese Beetle
The Japanese beetle (Popillia japonica) emerges as a distinct insect featuring a metallic green body and copper-colored wing covers. As adults, they cause significant damage by skeletonizing the leaves of over 300 different plant species.
May and June Beetles
Adult May beetles or June bugs (Phyllophaga) are generally larger and appear a robust, chestnut-brown color. Unlike the Japanese beetle, these adults are primarily active at night and are often seen clumsily flying toward outdoor lights.
European Chafer
The European chafer (Rhizotrogus majalis) develops into a golden-tan or light brown beetle approximately a half-inch long. The adult European chafer does not feed on foliage, focusing solely on reproduction during its short lifespan above ground.
Stages of Metamorphosis
The life cycle of the white grub involves four distinct stages: egg, larva, pupa, and adult, a process known as complete metamorphosis. Once the larval stage has completed its aggressive feeding phase and reached its full size, it prepares for the next transformation. The mature grub stops feeding and moves deeper into the soil, entering a pre-pupal stage where it empties its gut and forms a protective earthen cell. Within this cell, the grub molts one final time to enter the pupal stage, which is a non-feeding, resting phase. During this time, the insect’s body is completely reorganized from the larval form into the adult beetle structure. The pupa remains dormant for several weeks, protected by the surrounding soil until the adult form is ready to emerge.
When the Transformation Occurs
The timing of the grub’s transformation depends on the species, though the general cycle follows the annual seasons.
One-Year Cycles
For species with a one-year life cycle, such as the Japanese beetle and European chafer, the larvae that hatched the previous summer complete their feeding in the spring. They begin to pupate in late May and June, remaining in the soil for a short period before the adult beetles emerge. This emergence occurs in mid-summer, throughout June and July, initiating the next generation by mating and laying eggs.
Multi-Year Cycles
Species like the May or June beetle have a longer, multi-year life cycle, sometimes requiring two or three years to develop from egg to adult. These grubs overwinter multiple times before finally pupating and emerging in the early summer of their second or third year.