In The Dark
Image of Misumena vatia (cave spider) provided by © Ed Nieuwenhuys. Visit his Spider Gallery.
DB: This is Earth and Sky. For creatures that spend their entire lives in caves, there are no seasons and no day and night.
JB: These creatures of the dark are known as “troglobites.” They tend to be invertebrates such as spiders, centipedes, and millipedes that appear ghostly white. They’ve evolved from surface relatives, but lost their need for eyes and pigmentation.
DB: To locate mates and find food, troglobites rely on chemicals produced in their bodies called “pheromones.” If a troglobite stumbles on a new food source, it lays down a pheromone trail like the breadcrumbs in fairy tales so it can find its way back.
JB: Then, of course, predators won’t be far behind. And that’s where a heightened sense of smell and touch comes in handy. Troglobites generally have long legs and antennas so they can feel the vibrations of a nearby creature. Caves are tough enough on troglobites . . .
DB: And tougher still on the researchers who study them. Cave specialists crawl long distances underground and climb hundreds of meters below Earth’s surface. They take extreme care not to impact the habitat. Even a small crumb left behind could allow molds to grow that could throw off the ecosystem’s balance. But these researchers say the effort is worth it. With every trip, they bring to light species new to science. For today, that’s our show. Thanks today to the National Fish and Wildlife Foundation. We’re Block and Byrd for Earth and Sky.
If you enjoyed this program, you may be interested in the following websites:
Cave and Karst Management (National Park Service)
Cave Biology (National Park Service)
The National Speleological Society (Caves.org)
Biospeleology (University of Texas)
Biospeleology (Illnois Natural History Survey)
The Virtual Cave (GoodEarthGraphics.com)
Author’s notes:
Shane Fryer adds: the faunas that utilize caves are divided into three categories depending on their level of adjustment to the cave environment. The first group is known as trogloxenes. These organisms are opportunist who may occasionally shelter or forage within the twilight zone of a cave but don’t require caves to complete their life cycles. Raccoons are a good example of trogloxenes who sometimes utilizes caves as shelters. Trogloxenes are totally surface adapted. The second group is troglophiles who regularly travel outside of caves but require them for some portion of their life cycle. Some species of bats and cave crickets are good examples of troglophiles who foraging outside of caves at night and return to the cave to shelter, birth and hibernate. Though comfortable outside of the cave environment troglophiles have evolved special adaptations like echolocation and longer and more sensitive appendages, which allow them to navigate in the total darkness of the underground world. Finally the last category of cave adapted species is troglobites. These organisms are entirely cave adapted completing their entire life cycle underground and can not survive on the surface. Due to their lightless environment troglobites have lost their need for eyes and are totally blind existing with either the absence of eyes or greatly reduced optical structures. Instead of sight these creatures have evolved elongated sensitive antenna and appendages to navigate through their world. Often these organisms have evolved specialized pheromone glands and keen olfactory sense used to trace routes and track pray. These creatures are also characterized by very low metabolisms to deal with their low energy environment. Of the three categories troglobites are of special interest to the Cave Resource Management Program due to their interesting adaptations, rarity and endemic natures. Currently the only troglobites known in Sequoia and Kings Canyon are invertebrates who come in many forms. Troglobitic Life in Sequoia caves can be broken down into two groups the first includes predators like spiders, centipedes, scorpions and diplurans. The second are cave adapted millipedes, isopods, collembolans and homopterans who are the gazers and scavengers of the underworld imbibing sap from tree roots, forage on fungus and scavenging detritus.
The following person was interviewed for today’s show. Our thanks to:
Shane Fryer
Cave Technician
Sequoia and Kings Canyon National Parks
Three Rivers, California
Additional Teacher Resources
U.S. National Park Service, Sequoia and Kings Canyon National Parks; Nature and Science: Cave Biology
This article discusses the biology of the cave systems of Sequoia and Kings Canyon National Parks in northern California. The site provides extensive information on several troglobite species as well as several other subterranean life forms.
