A bog is a mossy, peat-covered or filled wetland on open terrain featuring wet, spongy ground made of decomposing vegetation and poor drainage. Bogs are habitats which lack oxygen, limit the decomposition of organic material and tend to result in nutrient poor, acidic environments on which few plants and animals will prosper. Most bogs are located in a depression or on flat ground, where the water table is at or near ground level and drainage is minimal. Bog environments by preserving organic material such as wood and prehistoric animal remains provide a valuable record of change in climate and vegetation. Plants that live in bogs have adapted to the difficult growing conditions. Many, such as the Pitcher plant, must catch and digest insects for nutrients.