Queen bat

Queen bats were large, hairy bat-like creatures that lived in the caves of Androzani Minor.

Biology
They had a three year life cycle, some of which was spent in a chrysalis. These chrysalises had a large supply of unrefined spectrox, which was refined and used by the humans of Androzani Major. It was also discovered, by Professor Jackij, that their milk could be used as a cure for Spectrox toxaemia. (TV: The Caves of Androzani)

History
The bats were killed or driven out by the mining androids, which caused them to move into the airless caves deep underground to die. With use of a half empty tank of oxygen, the Fifth Doctor had to climb down deep in the caves to obtain some Bat's milk to cure himself and Peri, who had contracted spectrox toxaemia. Sadly, he dropped the vial containing the bat's milk while trying to unlock the TARDIS, suffering from the paralysis stage of the infection. When he recovered the vial, most of the milk had leaked out and had left him with only enough to cure one person. The Doctor gave Peri the milk and, as she came round, he entered the late stages of the disease and regenerated as a result. (TV: The Caves of Androzani)