What the law requires
Regulation (EC) No 852/2004, Annex II, Chapter I requires food premises to allow good hygiene practice, including protection against pests, and Chapter IX requires adequate procedures to control pests. Article 5 asks for HACCP records that fit the size of the business. In the UK, the Food Standards Agency pack Safer food, better business has the same kind of pest checks. How often you check and what you do when you find pests come from your own HACCP plan and the national guide.
Pest control needs documented procedures. Mark the number and position of each trap on a floor plan.