Record: Weekly fly count, every bag removed with the reason and days since spawning, and the date of each floor wash.
Sketch the unit. Mark the dirty area (straw store, soaking drum) and the clean area (spawning, growing) and the door between them.
Put a hand-wash bucket and a change of footwear at that door.
Fit 35-mesh nylon net over every vent and door gap and check it for tears.
Hang a yellow light trap with an oiled sheet and count flies once a week.
Move all spent bags to a pit at least a field away and cover them.
Start a symptom page in the diary with the four questions: where, when, pattern, what changed.