A grub is the common name given to the larval stage of various scarab beetles, representing one of the most common and damaging pests found in lawns and gardens. These subterranean insects are responsible for significant turf damage across North America, often going unnoticed until feeding symptoms become severe. Understanding what a grub is and how it develops is the first step in protecting a healthy lawn.
Defining the Larval Stage
Grubs, often referred to as white grubs, possess a distinct physical appearance that makes them identifiable when unearthed from the soil. The most notable characteristic is their soft, milky-white body, which is typically curled into a pronounced “C” shape. They have a hardened head capsule that is usually a dark tan or reddish-brown color.
These larvae also have six jointed legs, which are clustered near the head. A fully grown grub can range in size from half an inch to over an inch and a half, depending on the specific beetle species. While the term “grub” is generic, it encompasses the larvae of several pest beetles, including the European chafer, Japanese beetle, and June bug.
The Beetle Life Cycle
Beetles that produce grubs undergo complete metamorphosis, which involves four distinct stages: egg, larva, pupa, and adult. The entire process for many common pest species, such as the Japanese beetle, spans approximately one year. However, some, like the June bug, have a life cycle that can last up to three years. Adult beetles typically emerge from the soil in early to mid-summer to mate and lay their eggs back into the turf.
The eggs hatch into tiny larvae in the summer, marking the beginning of the grub stage, which is the most destructive phase. Grubs feed on the grass roots throughout the late summer and fall, growing larger and causing increasing damage. As soil temperatures drop, the larvae burrow deeper to overwinter, emerging again in the spring for a brief period of feeding before they transition into the non-feeding pupa stage.
Signs of Grub Damage
An infestation often first appears as irregular, dead, or browning patches of grass that resemble drought stress, even after the lawn has been adequately watered. This is because the grubs have consumed the grass roots, preventing the plant from absorbing moisture and nutrients. When the root system is severely compromised, the turf will feel soft or “spongy” underfoot.
A definitive sign of grub damage is the ability to easily lift or roll back sections of the grass like a piece of carpet, as the roots anchoring the turf to the soil are severed. Secondary damage often confirms an infestation, as predators like skunks, raccoons, and birds are attracted to the lawn to feed on the grubs. These animals actively dig and tear up the turf, creating disturbed areas in their search for the larvae.
Effective Management Strategies
Controlling a grub population relies on proper timing and a combination of approaches. Cultural practices, such as maintaining a healthy lawn with deep, infrequent watering and appropriate fertilization, help turf tolerate low to moderate levels of grub activity. A robust root system makes the grass more resilient against the larvae’s feeding.
Biological controls offer an environmentally conscious method for management, utilizing natural enemies of the grub. Certain species of beneficial nematodes, microscopic roundworms that parasitize and kill the larvae, can be applied to the soil when grubs are actively feeding. Another biological option is Bacillus popilliae, or milky spore disease, which specifically targets Japanese beetle grubs.
For heavier infestations, chemical treatment may be necessary, and the timing of application is important for maximum effect. Preventative insecticides, containing active ingredients like chlorantraniliprole or imidacloprid, are applied in early summer to kill the newly hatched larvae before they cause significant damage. Curative products, such as those containing trichlorfon or carbaryl, are applied in late summer or early fall when the grubs are larger and actively feeding near the soil surface.