The answer to whether moths consume grass is complex, but generally, adult moths do not eat grass in a way that causes damage. The common misconception arises because the immature stage of many moth species—the larvae, or caterpillars—are significant pests of turfgrass and lawns. These caterpillars are the true culprits responsible for chewing on grass blades and stems, causing visible turf injury. The adult moth is merely the reproductive stage that lays the eggs which hatch into the destructive larvae.
The Critical Distinction: Moths Versus Larvae
Moths undergo complete metamorphosis, involving four distinct life stages: egg, larva, pupa, and adult. This cycle explains the dramatic difference in feeding habits between the two active stages. The larval stage, commonly called a caterpillar, is designed for rapid growth and food consumption. Larvae possess chewing mouthparts, known as mandibles, which are adapted for cutting and processing solid plant material like grass blades and stems.
Conversely, the adult moth stage focuses primarily on reproduction and dispersal, not feeding. Many adult moths possess non-functional, vestigial mouthparts, meaning they do not feed and rely entirely on energy reserves built up during the larval period. Other species, such as those with a long, coiled proboscis, sip liquids like flower nectar, tree sap, or fruit juices. An adult moth’s diet is never based on chewing solid grass, making the caterpillar the sole agent of damage.
Key Grass-Eating Larvae and Their Habits
Two frequently encountered types of grass-feeding moth larvae are the sod webworm and the armyworm, both known for their capacity to damage turf. Sod webworms, the larvae of small, tan “snout moths,” typically feed at night. During the day, they retreat into silk-lined tunnels or burrows constructed in the thatch layer near the soil surface. These caterpillars chew grass blades close to the crown, often leaving behind ragged or notched edges on the remaining foliage.
Armyworms are named for their tendency to feed in large groups. These pests are highly mobile and can consume vast quantities of turf in a short period as they deplete one food source and move to the next. Fall armyworms, for instance, are particularly fond of warm-season grasses like Bermudagrass. They can strip a stand of grass down to the stems almost overnight during heavy infestations.
Identifying Larval Grass Damage
Initial signs of moth larval infestation often look similar to turf suffering from drought stress, presenting as irregular, straw-colored patches that fail to green up after watering. A closer inspection, however, reveals evidence of feeding damage. Sod webworm feeding often creates areas where the grass appears closely “scalped.” You may also observe small, green, pellet-like droppings, known as frass, at the base of the grass blades.
Armyworm damage is identified by the “windowpane” effect on newly emerging grass. Young larvae scrape away the green tissue but leave the clear, upper layer of the leaf intact. If you disturb the grass in the evening, you may see small, tan or grayish adult moths flying low over the turf in a distinctive zig-zag pattern, indicating that eggs are being laid. Serious damage from both pests is most common in mid-to-late summer and early fall, particularly when the grass is stressed by heat.