Robbing season arrived early. The mesh went on before the sun cleared the fence line. It is not a barrier. Every forager in that colony is passing through it freely, and by afternoon they had learned the new route without a single one of them hesitating at the sill. The screen does not stop anything. It changes the geometry of the approach.
A robber arrives at speed, on a straight line, expecting an open entrance. The screen removes the straight line. The colony's own bees adapt in an afternoon because they live there. The ones who don't, never do.
A guard bee defends a door by standing in it. That is the entire method. There is no version where she covers forty inches at once.
So the door is narrower now. Not stronger.
Narrower.