Animals Wildlife 10 Creatures That Thrive in Caves By Bryan Nelson Writer SUNY Oswego University of Houston Bryan Nelson is a science writer and award-winning documentary filmmaker with over a decade of experience covering technology, astronomy, medicine, and more. our editorial process Twitter Twitter Bryan Nelson Updated May 31, 2017 Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species Kings of the underworld Photo: david__jones/Flickr [CC by 2.0] Trapped deep underneath the surface and left to evolve in isolation for thousands of years, cave animals are some of nature's most bizarre and fascinating creatures. Scientists call them "troglobites," and some species are so rare that they consist of a handful of individuals in a single cave. This is evolution at its most extreme, but troglobites are more common than you might think. Any time a new cavern is discovered, penetrated and explored, there's the potential of finding a new species. Here's our list of 10 incredible cave animals that have evolved to live in the darkness. (Text: Bryan Nelson) The olm Wiki Commons/GNU. This eyeless, white, dragon-like amphibian is called an olm. In fact, describing it as a dragon isn't that far from the truth. When they were first discovered in the 18th century, many people believed the creatures were baby dragons, a belief reinforced by the reality that they were only found in dark, aquatic caves. The olm is likely the first troglobite discovered, and to date it is also the largest. Some olms have been known to measure as much as a foot in length. Pseudoscorpion Gilles San Martin/Flickr. They look like the hybrid offspring of a spider and a scorpion, but pseudoscorpions belong to an arachnid order all to themselves. Although not all pseudoscorpions live in caves exclusively, many species do. For instance, scientists have recently discovered a new species of pseudoscorpion with venom-filled claws living in the deep granite caves of Yosemite National Park. Kaua'i Cave wolf spider Gordon Smith/U.S. Fish and Wildlife Service/public domain. Only known to live in a few lava tubes on the Hawaiian island of Kaua'i, this eight-legged predator is called the blind wolf spider by locals and is one of the rarest creatures in the world. In fact, researchers have never documented more than 30 spiders at a time. The wolf spider's closest living surface-dwelling relative has large eyes, like most types of wolf spider, but the Kaua'i wolf spider has completely lost its eyes because of the realm where it lives in isolation and darkness. Its favorite prey is another cave-dwelling creature, the Kaua'i cave amphipod, of which only 90 individuals are known to exist. Cave harvestmen Marshall Hedin/Flickr. Harvestmen look like spiders, but they are arachnids belonging to an order of their own. While many species live on the surface — like the bugs often called "daddy long-legs" — these animals are well-adapted to cave life and are some of the most commonly found types of troglobite. Tumbling Creek cavesnail David Ashley/U.S. Fish and Wildlife Service/public domain. This aquatic cavesnail lives on the underside of rocks inside of caves. It is only found in a few places in the Tumbling Creek area of southern Missouri. As with many troglobites, these tiny snails are extremely vulnerable once they are exposed to the surface world. Although their numbers were believed to be in excess of 15,000 individuals at the time of their discovery, a recent survey found no more than about 40 individuals alive. Devil's hole pupfish Stan Shebs/Wiki Commons/GNU. This fish is so rare that it is found only in a single aquifer-fed pool within a limestone cavern in Death Valley National Park. (This picture represents its entire natural range.) Despite relying on a shallow limestone shelf of only 2 meters (6.6 feet) by 4 meters (13 feet) for spawning, it has survived as a species for at least 22,000 years. Cave crayfish Marshall Hedin/Wiki Commons/CC License. Troglobites have adapted to cave life, which often offers a limited food supply. As a result, they typically have slow, energy-efficient metabolisms. Perhaps there is no better example of this than the cave crayfish (Orconectes australis), which is one of the world's oldest living creatures. It has been known to live for as long as 175 years. Cave beetle Wiki Commons/CC License. Feeding on carcasses of different cave animals and other organic material, Leptodirus hochenwartii is not something you want to meet on a spelunking adventure. This species was the focus of the first description of a cave insect, and before its discovery scientists weren't sure if insects could exist in caves at all. (Of course, this was long before the discovery of most of the world's troglobites.) Mexican tetra Wiki Commons/GNU. These fish are particularly fascinating because they come in two varieties. One variety is a normal-looking characin that swims in surface waters, and another variety is an eyeless albino that lives only in dark underwater caves. Since these varieties can breed together, they are technically the same species, but it is nevertheless an animal on the verge of speciation — a change driven by the remote cave habitat where the blind variety dwells. Texas blind salamander Steve Sims/Free Art License. Found only in the subterranean water systems of Edwards Plateau in Texas, this troglobite salamander is another underworld amphibian that could easily be mistaken for a baby dragon. Measuring at just under half a foot in length, these creatures were first collected in 1895 from a well that drew water from 58 meters below the surface. Like most troglobites, they have lost their sense of sight, an adaptation to their dark habitat.