The principal raw material of honey is the nectar collected from flowers, which produce it in order to attract pollinating insects and birds. Secondary sources include nectaries elsewhere on the plant and honeydew, the secretions of a particular group of bugs. The chemical composition of nectar varies widely, but its major ingredient by far is sugars. Some nectars are mostly sucrose, some are evenly divided among sucrose, glucose, and fructose, and some (sage and tupelo) are mostly fructose. A few nectars are harmless to bees but poisonous to humans, and so generate toxic honeys. Honey from the Pontic region of eastern Turkey was notorious in ancient Greece and Rome; a local species of rhododendron carries “grayanotoxins,” which interfere with both lung and heart action.