These are often called “paper moths” because they look like a light piece of paper blowing erratically in the wind. They are not often cause for concern. There are literally hundreds of species of moths that look very much the same. There is only one moth that is of concern and this is sod webworm. Fully matured sod webworms become moths that drop eggs onto the lawn as they fly. These eggs hatch and turn into the sod webworm larvae. Sod webworms are white in colour with an orange head. They are about half an inch long. They chew off the roots of the grass plants.
The first symptom of serious damage is the appearance of small, dead, fist sized patches. The lawn in these damaged areas peels up quite easily when gently tugged. Peel back the turf, and several sod webworms are likely to be seen.
Keep the lawn well watered. Avoid cutting until the sod webworms have been controlled using an insect control application performed by a professional lawn care service as soon as possible.
Small, damaged areas may fill in over several weeks but severely damaged areas may need to be replaced. Simply peel back the damaged turf and lay new pieces of sod over the exposed soil.
Bear in mind that just seeing paper moths over your lawn is not cause for immediate concern. The moths do not drop eggs full time and odds are extremely high that you are seeing a different species of moth. But it does mean you should keep a close eye on the lawn for signs of damage in the coming weeks.
If you see them in the late summer or fall, keep an eye on the lawn early next summer. In most instances, sod webworm damage goes unnoticed. If the eggs are spread far apart, sod webworm numbers may not be sufficient to cause noticeable damage.
A well cared for lawn may also be able to repair itself and re-tap damaged roots quickly enough to avoid damage.