Due to their fascinating biology and phenomena belonging to the realm
of scientific curiosity, cave animals have been objects of study for zoologists for
numerous decades. This chapter not only focuses on the extremes (e.g., absence
of eyes, specialization to extreme environments), but also serves as an introduction to understand the geographic distribution patterns and history of these highly diverse ecological groups with their relict characteristics. After an introduction to the subterranean environment in Sect. 1, we briefly review the biology and ecology of cave animals with their regressive and progressive evolutionary tendencies in order to understand the innate reasons for restricted distribution patterns (Sect. 2).
In Sect. 3, we summarize the main aspects of our knowledge regarding the distribution of these species, especially in the Holarctic;
and finally in Sect. 4, we highlight the relict characteristics of cave animal distribution and the ancient phylogenetic splits between cave and surface lineages.