The Fly Trap is one of the most delight-filled books I have read in years. It is a meditation on exactness and on love: in this case the love of an inconspicuous genus of flies that resemble little wasps. The subject sounds like pure Peter Cook: if bees have comic potential, how much more so a fly that doesn’t sting or collect honey or indeed do anything much except hang around on flowers looking sufficiently like a wasp to discourage predators? It turns out that there are more than two hundred species of hoverfly known in Sweden, and uncounted thousands around the world. Who would count them, and who would care?