Experts once considered cave dwellers to be evolutionary dead ends. Charles Darwin himself wrote of these “wrecks of ancient life,” and “living fossils.” But now we know better. As scientists find new cave species and probe their DNA, we’re learning that this hidden world is as dynamic as the one above ground. Far from being dead zones, caves are evolutionary laboratories.

The cave spider (Trogloraptor marchingtoni), first discovered in the dark zone of a cave in the coastal forests of Oregon, differs from other spiders so much that scientists created a new family to classify it. One feature that sets it apart: unmatched toothed claws at the end of each leg that are likely used for capturing prey.

Meet more amazing creatures in Life at the Limits, open for one more month!

The Incredible Cave Salamander

Described by Charles Darwin as home to "wrecks of ancient life," caves were once thought to be evolutionary dead-ends, cut off from the outside world and even from basic elements of life like sunlight. As it turns out, nothing could be further from the truth. Rather than halt evolution, the trying conditions of cave habitats, like total darkness and an unreliable food supply, force living things to develop incredible ways of coping with their extreme environments.

Since they’re facing the same set of general problems, cave-dwelling animals with no relation to one another tend to develop similar solutions. Species in caves often lack pigmentation and navigate and hunt with senses other than sight. One great example is the European cave salamander known as the olm.

These pinkish-white aquatic amphibians thrive in lightless, watery caves throughout eastern Europe. They eat, mate, and sleep underwater, breathing through external gills. Olms are also nearly blind, as developing eyes in a dark cave isn’t an efficient way to spend the body’s resources. The same principle accounts for the olm’s pallid coloration—pigmentation is an unnecessary luxury when you spend your life in darkness.

To compensate for their poor sight, olms employ a suite of highly developed senses terrifically suited to life in the waterlogged caves they call home. Special cells running the length of their bodies can detect tiny pressure changes caused by fish and creatures moving in the water nearby. Olms also boast organs that can detect the weak electric fields of animals around them, and specialized tissues in the salamanders’ inner ears grant them acute underwater hearing.

These heightened senses come in handy when an olm hunts its prey of cave-dwelling fish, crabs, and insects, which the salamander swallows whole instead of biting or chewing. Cave food sources can be fickle, though, and olms are as well prepared for famine as for feast. By lowering their metabolic rate and living on nutrients stored in their livers, they can survive for months at a time without a meal.

Find out about more amazing species thriving in exceptional environments in the special exhibition Life at the Limits, open now through January 3, 2016.

Most life on Earth depends on sunlight, but inside deep caves, darkness reigns. Despite being mostly cut off from the outside world, caves shelter an amazing array of organisms.

The walls of sulfur spring caves are often coated with microbes that scientists wryly call “snottites”—slimy mats of bacteria up to half an inch thick. Instead of using energy from the Sun, as green plants do, these bacteria draw energy from sulfur compounds to make their own food. Snottites can form the foundation of an unusual ecosystem in some caves, where many animals graze on the bacteria colonies as a source of food.

Meet more cave-dwellers in Life at the Limits: Stories of Amazing Species.

Image: Kenneth Ingham/NASA

Most animals that spend their lives in caves are blind and pale. Without light, eyes are useless, as are skin pigments, so animal populations that move into caves often lose these traits, evolving new qualities that are better suited for life in the dark. For instance, the olm, a long, thin salamander that lives in underground streams, is pigmentless and virtually blind, but possesses an acute sense of smell, sharp hearing, and organs that sense bioelectricity. It also boasts a line of specialized cells running the length of its body that can detect other animals moving in the water. Meet more amazing creatures in Life at the Limits: Stories of Amazing Species, now open!