About 2, 900 termites have been described worldwide. They undergo simple metamorphosis. They are eusocial insects and nymphs grow into one of the castes, where they will specialize in a job for the colony. A colony would consist of: a king, a queen, workers, and soldiers. The colony lives in nests, which are mostly built with saliva, mud, and soil. Nests are typically underground, but some can grow above the surface, with some of the tallest going thirty feet high. Termites have soft bodies that need to be kept moist and the nests provide the necessary protection and thermoregulation for the colony to survive. They frequently groom each other with their mouths. Termites feed on wood, leaf litter, or soil. They have bacteria in their gut, which aids with the digestion of cellulose. As detritivores, they play a huge role in nutrient cycling. They can be found in the fossil record as far back as the Late Triassic.