What is special about caves?
Caves are different from most other natural habitats in two respects.
First, they are always completely dark, darker than even the blackest night.
Second, the food supply is very limited. Because caves are dark, green plants cannot grow. Green plants provide all of the food, directly to plant eaters, indirectly to meat eaters, that animals need to grow and reproduce. Living in total darkness and without access to green plants cave animals need to alter the way they live, and the way they are, in order to survive. Broadly speaking there are two different sorts of animals that are found in caves: those that visit caves from time to time because they find safety and shelter there, and those that spend their entire life in caves’ darkness.
Two completely blind cave fishes.
Caves as shelters
Bats: Many sorts of bats are found in caves. In parts of the world with cold winters bats hibernate and for this they require a stable and protected place to sleep. Caves are ideal places because they are shelters from bad weather (with a permanent roof) and they have a constant temperature throughout the year. The Greater Horseshoe bat uses caves in southern England and is a protected species.
Bugs: Many insects (e.g., cockroaches) and spiders (e.g., giant crab spiders) shelter in caves because they like the high humidity and protection from predators. Others, such as moths, hibernate in caves just like bats.
A cave dwelling moth.
A giant running crab spider (Sparassidae) from a cave in Laos.
Caves as homes
Fishes: About 150 different sorts of fishes live permanently in caves. Many have been living in caves, and with no influence from daylight, for hundreds of thousands of years. They probably entered caves long ago because they were naturally nocturnal (night loving) animals. Surviving in dark, food poor caves is not easy but at least you can’t be eaten by birds or other predators! Some fishes managed to survive and as time passed they developed different ways of living and modified their bodies to help them survive in this peculiar environment. Many bodily changes have taken place but the most obvious ones are the absence of eyes, the fishes are blind, and absence of dark colouration, they look white or pink. Many people think of cave fishes as “blind white fishes”.
Salamanders: Between 10 and 15 sorts of salamanders live their entire lives in caves. Just like the fishes these salamanders loose their eyes and dark pigment. The most famous cave salamander is the Olm, which is found in caves in Slovenia and Croatia. It was though to be a baby dragon at one time! It is now known that there are three different types of Olm, one of which is actually black.
The olm from caves of central Europe.
Bugs: Over 50,000 different sorts of insects, millipedes, spiders or harvestmen are true cave dwellers. As with larger animals, they become blind and pale. Due to a poor provision of food and in average lower temperatures than outside, cave bugs have longer life cycles compared to those living outside.
A cave fresh-water shrimp.
Graham Proudlove & Dmitri Logunov
Nature Manchester 