Cave beetles
AN animal found only in underground caves and unable to exist above ground is called a troglobite. Troglobites normally inhabit caves with a stream, air at 100% relative humidity, and a completely constant temperature. Highly adapted cave insects are blind, pale or white, with long thin bodies, long antennae and long legs. Some lack both eyes and the optic nerve. Troglobite cave carabid beetles look much the same the world over. This is caused by convergent evolution in response to cave conditions. Whiteness and lack of eyes among inhabitants of vastly distant caves results mainly from the absence of natural selection against deleterious mutations affecting pigmentation and vision, neither of which are required in caves.
Troglobites typically have extreme compensatory adaptations for tactile, auditory and chemical stimuli — hence the long appendages and special sensory organs. Insects with those adaptations cannot disperse easily above ground and generally remain only in the cave system they evolved in. Consequently, they are more closely related to nearby surface species with normal pigmentation and sight than they are to troglobites which they resemble from other cave systems.
This shows clearly in New Zealand cave ground beetles, especially those in the tribe Trechini (family: Carabidae). Species after species from different caves are pale and thin, with long legs and antennae, and not only look much like each other but also resemble unrelated cave beetles in Eurasian and North American caves. Convergent evolution is so striking that in the recent past taxonomists in various countries have mistakenly put completely unrelated geographically distant cave carabid beetles into the same genera because of their resemblance.