I had these bugs all over my back yard even though I have no box elder
trees. Finally found they were Chinese rain tree bugs, a sub-species of
box elder bugs. They feed exclusively on the seed inside the little
lanterns. And of course I have a 35yo tree in my back yard. I got rid of
them by always catching the grass clippings, getting rid of all brush
piles, and lifting up many large river rocks where they breed. Last
year the backyard was truly infested. they would be all over the patio
mating. This year they are gone. Hope this helps.