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Did You Know?
In Did You Know? the National Geographic magazine team shares extra information we gathered to expand your knowledge of our featured subjects.
Troglobitic Paradise
Caves, homes for the world’s troglobites, can be created by volcanic eruptions. When hot molten lava flows downhill, it is slowly capped by freshly cooled rock and a lava tube forms. Once the erupting volcano stops, the resulting empty channel, or lava tube, remains. Being fragile, new tubes forming above older ones often cause the ceilings of the older tubes to break, joining the two together. Lava tubes, which lie close to the Earth’s surface, are usually less than 20 million years old. Fairly young on the geologic time scale.

Lava tubes frequently trap moisture, which can then be tapped by thin-rooted trees that reach through the tube’s surface while colonizing the rock above. The combination of dangling tree roots and moist, stable air creates a perfect habitat for many troglobites. Bayliss Cave in Australia is a lava tube with one of the most diverse troglobitic communities in the world, 24 known species.

One inhabitant of lava tubes in Hawaii is the Kauai wolf spider. Closely related to a surface-dwelling wolf spider with large eyes, the Kauai is often referred to as the “no-eyed, big-eyed wolf spider.” Producing fewer offspring than its relative, the female Kauai wolf spider will carry her spiderlings on her back after they hatch until the youngsters are ready to leave and hunt on their own. With only three populations of this troglobitic spider known to exist, the U.S. Fish and Wildlife Service listed it on the endangered species list in January 2000.

—Emily Fekete