This is a simple fly trap designed to fit over the rim of a standard empty tin can. The principle is that flies are attracted into the can by the scent of a bait then fly up towards the light and air through the slots in the top. They eventually tire and fall to the bottom of the can where they drown in some water.Put a small piece of bait in the bottom of the can (liver works really well) then pour 10-20mm of water in the bottom of the can. Clip the trap top on and place the can somewhere warm where flies will find it. Within 24 hours there should be flies entering the can and not coming out.You could probably just use dry bait if you wanted to keep the flies alive as food for frogs etc.