True bugs are diverse, ranging from tiny lace bugs to large water boatman. Their diets are diverse as well, but all true bugs feed by piercing and sucking food. The beak-like mouthpart of a true bug is like a trough that folds back under its body. One channel of the trough sends saliva out to moisten food, while the other channel sucks liquid food in. Despite their similar feeding apparatuses, the diets of true bugs vary. Many feed on sap, sucking it out of leaves, flowers, stems, shoots, or roots. Others are predators, using sharp beaks to stab small prey such as snails. Parasitic true bugs, such as bed bugs, pierce the skin of mammals or birds and feed on their blood. More unusual diets include jellyfish or fungi from under tree bark. The piercing and sucking technique even allows some true bugs to liquefy and eat mosses or seeds.