Why are wasps attracted to grass?

Well...

A wasp's nest is his castle, and he will defend it with utmost ferocity. If you see a nest, leave it well alone. Wasps are also attracted to light, so as it starts to get dark, try to avoid switching on outdoor lamps or using candles until you really have to. That is what they do and why they do it is because...

Many insects other than moths are attracted to light, in fact most insects can be found in greater or smaller numbers at light traps. Often in lighting strips you will find many insect species that have simply been attracted there by the light, moths, flies etc, and sometimes wasps. They seem to be able to find their way in not out again.

Wasps are carniverous insects and will cut up and eat or take to their nest for the larvae to feed on, almost any creature or part thereof. They may be able to scent the dead insects in the light fittings, or it may just be the light that attracts them. They certainly won't be there to lay eggs. Only the Queen wasp can do that and she builds a nest for that purpose.

This Information was got from Harry Eales Ancient Entomologist

Hope this helped :)