While watching TV on a warm summer evening I like to leave the curtains open so I can watch the bats swooping outside. Not very fuel efficient bats - some need to eat their own body weight in insects each night. That's a heck of a lot of midges, rather fewer large moths. So recently I took the plunge and built myself a light trap (investing a whole £4.95 in a blacklight banknote checker from eBay - works great with a white sheet draped over a lawn chair).