The term “lawn worm” is a common, yet ambiguous, description for organisms found beneath turf. This general name can refer to either highly beneficial soil dwellers that support grass growth or destructive insect larvae that actively feed on the root system. Understanding which creature is present in your soil is the first step in deciding whether to encourage its presence or take steps to remove it. Misidentification can lead to inadvertently harming the allies of your lawn or allowing a pest infestation to continue unchecked.
The Beneficial “Worm”: Earthworms
The true beneficial “worm” found in lawns is the earthworm, a terrestrial invertebrate belonging to the phylum Annelida. These organisms are easily identified by their long, cylindrical, and segmented bodies, often exhibiting a reddish-brown or pinkish-gray color. Unlike insect larvae, they have no legs. A mature earthworm features a smooth, saddle-like band called the clitellum about one-third of the way down its body.
Earthworms are foundational to soil health through their constant movement and feeding. As they tunnel, they create channels that naturally aerate the soil, allowing water and oxygen to reach grass roots. This burrowing activity also improves soil structure and enhances water infiltration, reducing runoff and compaction. Earthworms consume organic matter, such as dead leaves and thatch, and excrete nutrient-rich waste known as castings, which act as a natural fertilizer for the grass.
The Common Lawn Pests Mistaken for Worms (Grubs)
The destructive creatures often misidentified as lawn worms are white grubs, which are the larval stage of various scarab beetles, including Japanese beetles, June bugs, and masked chafers. These pests cause extensive damage by feeding on grass roots. White grubs are typically creamy white, plump, and grow up to about one inch long.
A distinguishing physical characteristic is their C-shaped posture when found in the soil, along with a noticeable dark brown head capsule. Unlike earthworms, grubs possess three distinct pairs of legs located near their head. They remain in the larval stage for an extended period, often up to a year, with the most severe damage occurring in the late summer and early fall when they are larger.
Identifying Signs of Infestation and Damage
The differences between a healthy earthworm population and a damaging grub infestation become evident in the lawn’s appearance. Grub damage often first appears as irregular, scattered patches of brown or yellow grass that do not respond to watering. The turf in these areas will feel spongy or soft underfoot because the grubs have severed the root system, causing the connection between the grass and the soil to weaken.
A simple diagnostic test is to grab a handful of grass in a damaged area and gently pull upward. If the turf lifts easily, like a loose piece of carpet, grubs are likely the culprit. To confirm the presence, a small square foot section of turf can be carefully lifted to a depth of about three inches. Finding ten or more C-shaped grubs in that square-foot area indicates a serious infestation that requires treatment. Secondary indicators of a grub problem include increased activity from animals like skunks, raccoons, and birds, which dig small holes in the lawn while foraging for the larvae.
Management Strategies for Lawn Health
Managing the subterranean population involves two distinct approaches: promoting beneficial earthworms and controlling destructive grubs. To encourage earthworms, cultural practices should focus on maintaining a chemical-free, organic environment. Reducing the use of synthetic pesticides and fertilizers is beneficial, as these can be harmful to earthworms. Incorporating organic matter through topdressing or leaving grass clippings provides a steady food source, which helps sustain a healthy earthworm population.
Controlling grub populations requires precise timing, as treatment is most effective when the larvae are small. Biological controls offer environmentally conscious options, such as applying beneficial nematodes, which are microscopic roundworms that parasitize and kill grubs without harming earthworms. Another option is Paenibacillus popilliae, known as milky spore, a bacterium that specifically targets Japanese beetle grubs and offers long-term control. For severe infestations, chemical controls like curative insecticides containing active ingredients such as trichlorfon are typically applied in late summer or early fall when grubs are actively feeding near the surface.