Tangent Short Fiction Review had this to say:
“Paid in Full” by Susan Forest tells of two um bug farmers on another world, and the giant gnats which, depending on their kind (Dark/good or White/bad), lay eggs which are nourished by the aphids and then sold, or are the rogue and deadly variety which appear at dark and kill everything they can in their feeding frenzy. One of the farmers has hit hard times and asks a favor of the other, who is forever repaying the former for a long ago debt. But now the debt has been repaid in full, and the first farmer is still extremely ungrateful (his friend has just saved his life). The story is a lesson in learning when to let go of a debt repaid when one learns that one is being taken advantage of. The gnat/aphid symbiosis, and how the eventual product is processed for profit is entertaining, as is the scene of the night terror a swarm of the deadly, blood-sucking White gnats wreaks on the terrified farmers.