Terrestrial oligochaetes are commonly known as earthworms and burrow into the soil. The four main families with large numbers of species are Glossoscolecidae, Lumbricidae, Megascolecidae and Moniligastridae. Earthworms are found in all parts of the world except for deserts. They have a requirement for moist surroundings and the larger species create burrows that may go down several metres (yards) while young individuals and smaller species are restricted to the top few centimetres of soil. The largest numbers are found in humus-rich soils and acid soils. A few species are found in trees, among damp moss and in the debris that accumulates in leaf axils and crevices; some others make their homes in the rosettes of bromeliads.