7 Animals Adapted to Living in Total Darkness

1. Kaua’i Cave Wolf Spider (Adelocosa anops)

Like with many small cave insects, the Kaua’i cave wolf spider isn’t easy to find. It was first discovered in 1971 and is only found in a few areas in Hawaii. Most wolf spiders are easily identified by their unique eyes. They have a total of eight eyes, but there are two large ones in the middle row. However, these cave wolf spiders are completely lacking eyes.

Thanks to the sensory hairs on their legs, this spider can sightlessly catch prey. While many spiders have sensory hairs, the Kaua’i cave wolf spider has adapted to cave life by growing even longer hairs. This allows them not only to sense the smallest of sounds from a distance but also to safely navigate through caves.

2. Olm (Proteus anguinus)

Olms are cute and small animals that are surprisingly resilient. Research has found that they can live up to 10 years without food. They’ve also been found to live to at least 58 years old.

This ancient species began branching off from other amphibians about the same time birds evolved. The olm is well-adjusted to the total darkness of their cave habitat. They can’t see, but their other senses are highly refined, including their fascinating electrosensitivity. Olms are also uniquely the only European vertebrate that lives in caves for their entire life.

3. Dinner Plate Jellyfish (Solmissus)

The dinner plate jellyfish belongs to the Solmissus genus. Its name comes from their rather flat shape, instead of the cup or bell shape that many other jellyfish have. They live in complete darkness deep in the ocean. Dinner plate jellyfish are commonly found around 2,300 to 3,300 feet under the surface of the water.

Unlike other jellyfish, the dinner plate jellyfish actively hunts for prey. They are often found with their tentacles facing up, searching for nearby plankton. Researchers do not know much about these jellyfish, as they live so deep in the ocean.

4. Remipede (Remipedia)

So far, the remipede has been found only in karst systems in Central America, the Canary Islands, Western Australia, and the Caribbean. Though they were first described in 1981, biologists don’t know much about these animals. Remipedes swim on their backs, have 32 trunk segments, and possess both male and female sexual parts. Because they live solely in dark caves, they lack both pigmentation and eyes.

5. Northern Wolffish (Anarhichas denticulatus)

Northern wolffish have adapted to handle the harsh environment of 5,500 feet below the surface of the ocean. They prefer cold waters like those of the North Atlantic. To combat the cold, wolffish contain a compound that prevents blood from freezing.

These animals can seamlessly alternate between relatively shallow ocean levels (around 400 feet) and 4,000 feet or lower without a problem. Because they lack a buoyancy sack, they must continually swim, or they will sink.

6. Giant Tube Worms (Riftia pachyptila)

Not only do giant tube worms live in total darkness, but they also live without oxygen, a mouth, or an anus. These marine animals live near hydrothermal vents, consuming the hydrogen sulfide that comes out of the vents. They are considered extremophiles thanks to their unique and harsh living environment.

Tube worms are able to survive with the help of symbiotic bacteria. The bacteria convert the hydrogen sulfide into nutrients for both organisms through a process known as chemosynthesis. The bacteria benefit from the relationship by receiving a safe home and nutrients. Despite adapting to darkness, the giant tube worm has retained color. Specifically, their plume is bright red.

7. Mexican Tetra (Astyanax mexicanus)

A small fish species known as the Mexican tetra lives in caves and are completely blind. In fact, they lack eyes entirely. Like other dark environment animals, they are incredibly pale. Fairly recently, researchers have discovered that these little fish evolved to communicate in the darkness and are capable of making noises to warn about predators. Additionally, groups in different caves appear to use different sounds to communicate.