Thrive and Endure

Part of the Life at the Limits exhibition.

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. Many of these animals have adaptations like long limbs and well-developed sensing organs that help them move and find food without light.

Caves are far from the only intense environments where life can take hold, though. While most organisms try to stay away from freezing cold, boiling heat, and harsh chemicals some—called extremophiles, or “extreme-lovers”—actually thrive in environments like these. While taking up such harsh habitats seems counter-intuitive, living where few other species can is a great way to avoid competition.  

Creatures of Darkness

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.

A pigmentless salamander with undeveloped eyes stands alert in a dark cave.
The cave-dwelling olm is blind, but has great senses of smell and hearing.
Arne Hodalic / Creative Commons

A Bacterial Buffet

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.

Snottites, thick, drippy bacterial material hanging from the bumpy rock ceiling of a cave.
Researchers found this snottite in a cave in Mexico.
Kenneth Ingham/NASA

Running Hot and Cold

Whether scalding or frigid, environments with intense temperatures can feel “just right” to species of extremophiles adapted to live there. Microbes living near hydrothermal vents in the deep ocean can thrive and reproduce at 235˚F (113˚C)—hotter than the boiling point of water at sea level. At the other end of the thermometer, ice worms can be found wriggling through the melting snow of Alaskan glaciers in the spring. These creatures complete their entire life cycle in the ice and snow of glaciers, burrowing away from the surface when the sun warms their snowy homes.  

Hydrothermal Vents
A hydrothermal vent in the northeastern Pacific Ocean.

The Species in the Spring

At scenic Yellowstone National Park, entire food chains depend on bacteria that live in the near-boiling water from local geysers and hot springs, enduring temperatures up to 175˚F  (79˚C). Colorful cyanobacteria cover the wet rocks; flies consume the bacteria; mites live on the flies; and the flies are eaten by predatory wolf spiders. 

grand prismatic spring
The astounding colors of Yellowstone's National Park's Grand Prismatic Spring are produced by several species of bacteria that thrive in the hot spring's waters. 
© NPS/J. Peaco 

Get up close and personal with a model hydrothermal vent and spelunk into the lightless world of numerous cave creatures in Life at the Limits.