You may possibly have some Crane Flies which would be harmless to your lawn. The larva may feed on decomposing organic matter but the adults do not feed at all. They are essentially harmless to any lawn.

Not quite so fast, Kimmsr. In some parts of the country, cranefly larvae (called leather jackets), are true pests of lawns. The European Cranefly, in particular, can be a problem if the populations are high enough.

West, you are observing the adults laying eggs.

Since 1945 the use of pesticides has increased 10 fold while damage from insect pests has doubled and today bees, the pollinators of about 1/3 of our food, are threatened with destruction because we are, simply, too quick to lable most anything a pest that needs to be controlled, preferably by some kind of poison. With few exceptions my sources tell me that Crane Flies primary food source is decaying organic matter and while large populations may be a nuisance they are not harmful pests.

Here is a link that might be useful: Crane Fly

i don't think i would have had enough of them to bring on a '
problem' in the spring when they emerge, hope not anyway.

I guess the compost I top dressed my fall grass seed with is probably what brought them in...

West, the problem is not with the adult cranefly, but with the larvae in the soil. In large enough numbers, they can cause problems for lawns by eating the roots. Most serious complaints appear to be in the PNW (in this country), though I have seen major populations in pockets in the South.

In most situations, feeding from leatherjackets causes little problem for a lawn that is managed properly. This means timely mowing at the right height, smart nutritional attention, watering only when the lawn needs it, and other good management practices. Keeping the root system strong with occasional core aerifying can boost the turf grass vigor enormously, too.

Leatherjacket damage can look like that from grub or sod webworms, just so you know.