Those white, silky webs you’re seeing in your grass are most likely one of three things: actual spider webs, fungal growth, or caterpillar silk from sod webworms. All three show up most visibly in the early morning when dew clings to the strands, and each one looks slightly different once you know what to look for.
Grass Spiders: The Most Common Cause
The webs you’re noticing are most often built by grass spiders, a group of funnel-weaving spiders in the genus Agelenopsis. These spiders construct flat, horizontal sheet webs in dense grass, mulch, and low-growing shrubs like junipers. The webs become dramatically visible when morning dew settles on the silk, turning your lawn into what looks like a field of tiny trampolines.
A grass spider web has a distinctive shape: a broad, flat sheet with a narrow funnel or tunnel tucked into one corner, usually extending into a hidden spot in the grass. The spider waits at the entrance of this funnel and rushes out when an insect lands on the sheet. The silk itself isn’t sticky. Instead, vertical strands above the sheet act like trip wires, knocking flying insects down onto the flat surface where they get tangled just long enough for the spider to grab them.
Grass spider webs are completely harmless to your lawn. The spiders are beneficial predators that eat insects, and they have no interest in people. If the webs bother you visually, they’ll typically become invisible once the dew dries. Mowing disperses them temporarily, but the spiders will rebuild.
Fungal Mycelium: When the “Webs” Are Disease
Not everything that looks like a spider web in your grass actually is one. Dollar spot, a common lawn fungus, produces short, fuzzy white threads called mycelium that sit on top of grass blades and look remarkably like tiny cobwebs. This growth appears in the early morning when dew is present and vanishes as the grass dries, which makes it easy to miss entirely if you’re not outside at the right time.
The fungus becomes active in spring once nighttime temperatures stay above 50°F, and it continues through summer until daytime highs consistently exceed 90°F. It thrives on prolonged leaf wetness, needing 10 to 12 continuous hours of moisture to infect grass. Heavy dews during cool late-spring and early-summer nights create ideal conditions. Every grass species can be affected, though certain varieties of bentgrass, perennial ryegrass, and Kentucky bluegrass are especially vulnerable.
The key difference from spider webs: fungal mycelium disappears as morning moisture evaporates, and the grass beneath it starts turning yellow. If you’re seeing small, straw-colored patches a few inches across along with the morning webbing, dollar spot is the likely culprit.
Sod Webworm Silk
A third possibility is silk produced by sod webworm larvae, the caterpillar stage of small lawn moths. These caterpillars spin silk tunnels and webbing close to the soil surface, where they hide during the day and emerge at night to chew on grass blades. The silk is usually found close to the ground rather than draped across the top of the grass like spider webs or fungal mycelium.
Sod webworm damage looks different from fungal damage. You’ll see small brown patches that appear scalped or closely clipped, and these patches grow larger as the caterpillars keep feeding. Other telltale signs include tiny green fecal pellets in the thatch layer and an unusual number of blackbirds poking holes in your lawn as they probe for caterpillars. Most species produce two to three generations per year, with the heaviest damage coming from overwintered larvae in spring.
How to Tell Them Apart
A close look in the early morning, when dew makes everything visible, will usually give you the answer.
- Grass spider webs have a flat sheet shape with a funnel or hole in one corner, and the threads radiate in a circular pattern. They stay visible after the dew dries (though they’re less obvious). The grass underneath is perfectly healthy.
- Fungal mycelium looks like fine, fuzzy white threads sitting on top of the grass blades. It disappears completely once the dew dries. The grass below turns yellow or straw-colored within days.
- Sod webworm silk is found closer to the soil in tube-like tunnels rather than spread across the grass tips. Look for chewed-down grass blades, green pellets, and expanding brown patches.
Managing Fungal and Insect Webs
Grass spider webs don’t need any management. The spiders are eating pests and will relocate on their own as the season changes.
For dollar spot, the most effective approach is reducing how long your grass stays wet. Water your lawn in the early morning so blades dry quickly in the sun, rather than in the evening when moisture lingers overnight. The fungus needs those 10 to 12 hours of continuous wetness to take hold, so breaking up that window is the single most impactful thing you can do. Maintaining adequate fertility also helps, since underfed lawns are more susceptible. Mowing at the right height for your grass type and removing excess thatch improves air circulation around the blades.
For sod webworms, start by confirming they’re actually present. Part the grass in a brown patch and look for silk tubes, green pellets, and the caterpillars themselves, which are small, tan or greenish, and about half an inch to an inch long. If birds are tearing up your lawn in concentrated areas, that’s a strong signal. Healthy, well-watered lawns can tolerate light webworm feeding and recover on their own. Heavy infestations in stressed lawns may need targeted treatment with products containing Bacillus thuringiensis (Bt), a naturally occurring bacterium that kills caterpillars without harming other organisms.