Lawn grubs are the destructive larval stage of various scarab beetles, such as the Japanese beetle or the masked chafer. These immature insects live just beneath the soil surface, where they voraciously feed on the tender roots of your grass. This root-feeding activity leads to noticeable damage in the lawn, often appearing in late summer or early fall when the grubs are at their largest and most active. This guide outlines the indicators and the physical inspection method necessary to confirm a grub infestation.
Initial Visual Indicators
The earliest evidence of a grub problem often appears as irregular patches of brown, dying grass in the lawn. Unlike the uniform browning caused by drought, grub damage typically shows up in scattered, oddly-shaped areas that do not respond to watering.
Another distinct characteristic is a change in the turf’s texture, which may feel spongy or soft when walked upon. This sensation occurs because the grubs have consumed the root system that normally anchors the grass firmly to the soil. In cases of heavy infestation, the grass in these brown patches can be easily lifted or rolled back like a piece of loose carpet, exposing the soil underneath. This “tug test” is a quick initial confirmation that the grass has been severed from the soil base.
Signs of Secondary Foraging
The presence of grubs can often be indirectly confirmed by the activity of animals that feed on them. Raccoons, skunks, moles, and various birds, especially crows, are common predators.
Their foraging behavior results in localized damage that is distinct from the grubs’ own root-feeding destruction. You may notice small, cone-shaped holes, divots, or larger sections of torn-up turf where animals have actively dug to uncover the pests. This secondary damage often appears overnight and is concentrated in the areas where the grub population is densest, indicating a large infestation.
Conducting the Physical Inspection
The only way to definitively confirm an infestation and determine its severity is by conducting a physical inspection of the soil. Use a spade or a sharp instrument to cut a one-foot square section of turf, approximately two to four inches deep, where the majority of grubs reside.
Carefully peel back this square of sod, much like lifting a flap of carpet, and examine the soil and the underside of the grass flap for the larvae. It is most effective to sample the healthy grass bordering a damaged area, as grubs are often moving from dead sections into the intact roots. Counting the number of grubs found within this square-foot sample provides the necessary data for treatment decisions.
A healthy lawn can typically tolerate a low population of grubs, with five or fewer per square foot generally not warranting treatment. However, finding a count of six to ten grubs or more per square foot indicates a moderate to severe infestation that requires action. After inspection, the sod can be replaced and watered to encourage recovery.
What Grub Larvae Look Like
The larvae, commonly referred to as white grubs, are plump, soft-bodied insects with a creamy white or gray-white color. When disturbed, they instinctively curl their bodies into a tight, characteristic “C” shape.
Grubs have a distinguishable reddish-brown or chestnut-colored head capsule. They possess three pairs of legs near the head. Depending on their age and species, their size can range from a quarter of an inch up to a full inch in length when mature. The rear end of the grub may appear darker due to the soil and organic matter they ingest.