What a cleaner sees that nobody else does
Cleaners work behind and under things. Bin rooms, service corridors, kitchen plinths, the gap behind a fridge, storage areas that are opened once a week. Those are exactly the places where activity appears first, and they are areas most staff and managers never look at closely. A cleaner who reports what they see gives a building weeks of warning it would otherwise not have.
The observations worth reporting are concrete: droppings and their location, gnaw damage, nesting material, unusual odours, insect activity, and structural gaps such as a failed door seal or an open penetration. Reporting a sighting is useful; reporting a location and a description is far more useful, because a pest technician can act on it without repeating the search.
