Both naturally occurring caves as well as mines and tunnels created by human activity can be found throughout Wisconsin and are important and unique subterranean features. They often have an opening to the surface but are characterized by little or no light. Structure, geology, and hydrology are other dominant ecological influences. Caves form from the dissolution of several rock types including limestone, dolomite, and gypsum, which differ in their chemical composition and rates of erosion, and influence cave size and structure. The distinctive biodiversity and geologic formations in caves and artificial subterranean openings depend on unique and specific environmental conditions. Bats, raccoons, salamanders, and many invertebrates, including a number of rare macro-invertebrates including springtails, amphipods, and isopods are known to use or inhabit these systems. Caves, mines, tunnels, and similar underground structures provide summer roosting and winter hibernating sites for significant numbers of bats.
