I think it was in a sci fi anthology about 25 years ago. The human in the story is aware of them as little bugs which won't leave him alone. They are trying to pay him back for help he gave them unknowingly with their research. (I think.)
He is under a lot of pressure at work because he needs to find a way to recycle plastic or something. The aliens keep trying to help him and he keeps throwing their work away, unaware of what they are doing.