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The little known impact of bats and bat guano in the late stages of cave morphogenesis. Bats are considered as symbolic caves inhabitants. The colonies, sometimes huge, may occupy caves through long periods. Large guano deposits were accumulated. Some have been mined for phosphates, either by hand or at the industrial scale. Bats impact is triple: breathing releases CO2, urine is corrosive, and guano mineralization releases acids (carbonic, nitric, sulfuric, and phosphoric). Such aggressive compounds have an effect on carbonate rock and flowstones, either by direct ground corrosion at the contact of the guano, or by condensation-corrosion on walls and ceilings. The speleogenetic impact of these late stages of cave evolution is considerable and may provoke denudation of several meters of rock. The long lasting presence of bat colonies is a major factor of the late speleogenetical stages, making specific morphologies, significant phosphate deposits, and wall reworking ranging from some centimeters to several meters. These corrosion morphologies, sometimes misinterpreted as marks of flooding, are also responsible of the destruction of many prehistoric realizations, which have been preserved only in specific conditions.