Does anyone know if yellow jackets avoid flying on hot day and will only come out at night?

Saw hundreds of flying small yellow and black bugs that looked like yellow jackets last night while walking the dog. They were swarming the grassy areas and luckily they didn’t seem to bother with anyone, even my dog.
If they were yellow jackets, wouldn’t they have stung us?

Unfortuately I didn’t have my reading glasses on so I could not make out any fine details. Just the shape and the coloring.
If they are not yellow jackets, than what could they be. They were too skinny and small to be bumble bees. Of course I have never seen newly hatched bumble bees, so maybe they are smaller.