Bladderwort

a curious aquatic herb floating or rooting in the mud. The thread-like leaves are furnished with air bladders which float the plant, especially at time of flowering. An interesting feature is a light, thin, trapdoor opening inward on the underside of the bladders. The probability is that this door is designed to admit water when the plant is ready to sink, but insects push up through the trap and are unable to escape. The question is whether the plant makes use of them for food. The yellow flower of the common bladderwort (utricularia vulgaris) has a chin-like spur and an irregular sort of hood. It grins at one from ponds and ditches like a tiny old water witch.