In our office at work, a couple of people claimed to have been bitten by unseen pests. The caretaker came into the office and strategically placed sheets of white A4 paper on the floor and said to leave them there overnight an if there were any pests there would be evidence on the paper in the morning. I naively asked what he'd sprayed the paper with and he said nothing because they'd be attracted to white surfaces. He claimed he's a qualified pest controller so I was in no position to challenge him. Nothing was found on the paper the following day but is he right? On a lighter note, one of the night duty staff walked in an slipped on one of the sheets of paper and went flying!