What happens if my hens eat fly maggots?

Their digestive tracts will kill the maggots without doubt, and the eggs, though ping through their digestive tract, come from the ovaries, so there's no way the parasites would find their way under the shells! The hens will get some extra protein from the flies or maggots, but that is about the only thing that will happen. Hunting insects is one of the few pieces of entertainment that captive animals get, so let them enjoy.