Piotr Naskrecki / Angolan free-tailed bat (Mops condylurus) close up of teeth. Codzo Caves, Mazamba, Sofala, Mozambique. Controlled conditions

Piotr Naskrecki / Angolan free-tailed bat (Mops condylurus) close up of teeth. Codzo Caves, Mazamba, Sofala, Mozambique. Controlled conditions

Juan Carlos Munoz / Tourists looking down onto underground stream, from illuminated pathway, Skocjan Caves, Green Karst, Slovenia, October 2014.

MYN / Gil Wizen / Soil centipede (Geophilidae sp), Caves Branch, Cayo District, Belize, September. Focus-stacked. meetyourneighbours.net project

Vincent Grafhorst / Stalagmites and stalactites in cave chamber, Gcwihaba Caves, Botswana

Inaki Relanzon / Lesser Horseshoe Bat (Rinolophus hipposideros) hibernating in Forat de l'Or cave in Terradets Canyon, Pyrenees, Lleida, Catalonia, Spain, December

Jabruson / Sundevall's Leaf-nosed Bats (Hipposideros caffer) in flight in forest roosting cave. Bai Hokou, Dzanga-Ndoki National Park, Central African Republic.

Mark Carwardine / Mark Carwardine and Douglas Adams on location for BBC radio series 'Last chance to see' in Robinson Crusoe's cave, Juan Fernandez Islands, Chile, December 1988

Solvin Zankl / Schreiber's long fingered bat (Miniopterus schreibersi) in flight in cave, Grotta Monte Majore, Sardinia, Italy. Highly commended, Mammals category, GDT 2012 competition.

Eric Medard / Lesser Mouse Eared Bat (Myotis blythii) in flight in cave. France, Europe, August.

Eric Medard / Mediterranean Horseshoe Bat (Rhinolophus euryale) in flight in cave. France, Europe, August.

Eric Medard / Bechstein's Bat (Myotis bechsteinii) in flight in cave. France, Europe, August.