The Biology of Caves

Unlike the surface environment that is very changeable, cave environments are constant. It is a world of total darkness, constant temperature and high humidity. The animals that live in caves must not only adapt to these conditions, they must live in an environment where there is very little to eat.

The population of animals living in caves is very small compared to the animal life on the surface. Consequently, a number of cave animals are on the endangered species list. This means that they are in danger of becoming extinct.

 

Scientists are just now beginning to appreciate the amazing role that micro-organisms, including super small "nanobacteria" play in cave systems.

The Cave Food Chain
All life depends on sunlight, even in the darkest areas of a cave. No green plants grow here because they need light for photosynthesis. On the surface, green plants make food. Cave animals must depend on occasional floods to wash leaves, twigs and plant debris into the cave. Another food source is provided by droppings from animals that go outside to feed then return to the cave to sleep or raise their young. The droppings from animals, such as bats and crickets, may provide the only major food source in some caves. Few animals can directly feed on these droppings. Instead, bacteria and fungi decompose these materials into simple foods and nutrients.

Fungus-eating insects, such as beetles and mites, feed on the fungi and bacteria on animal droppings and plant debris. These animals then become the food supply for the larger predators like salamanders or crayfish. The droppings from larger cave animals replenishes the food supply for fungus and bacteria. Thus the food chain continues.

All species in the cave system are dependent upon each other for survival. Remember, the number of animals in a cave is far fewer than their relatives on the surface. For these reasons we remember: DO NOT DISTURB life within a cave.

 

Blind cave fish adapt by having sensory cells in their skin that detects movements in the water nearby.

Rick Olsen, NPS

Types of Cave Life

Cave animals fit into three categories based on the amount of time they actually spend in the cave.

Trogloxenes: from the Greek words "troglos" (cave) and "xenos" (guest). They are temporary cave residents which freely move in and out of the cave. These cave visitors seek out such a habitat from choice, and never complete their entire life cycle in the cave. Bats are usually the first trogloxenes that come to mind. Some species prefer the constant temporature of caves for hibernation and to bear their young. Bats, bears, skunks, moths, and people are examples of trogloxenes. Many of these animals are not dependent on the cave for their survival, they show no special adaptations to the cave environment.

Troglophiles: from the Greek words "troglos" (cave) and "phileo" (love). These cave loving animals can live in the dark zones of a cave, or they can also survive outside the cave. At times they will venture out in search of food. This group includes earthworms, some beetles, cave crickets, frogs, salamanders, and some crustaceans (such as crayfish).

Troglobites: from the Greek words "troglos" (cave) and "bios" (life). They are the true cave dwellers which spend their entire lives in the cave. Living permanently in the dark zone, these species are found only in caves and cannot survive outside the caves.

Troglobites have developed special adaptations to help them survive in caves. Since cave food sources are meager, the sense organs and physical resources of troglobites are devoted to finding food. Sense organs and physical adaptations that are beneficial to the animals’ survival are enhanced. Sense organs that are not necessary have degenerated.

Most troglobites are white to pinkish in color. They lack pigment (color) because they have no need for protection from the sun’s rays or for camouflage to hide them from predators. Many have no eyes or eyes that are poorly developed. Eyes are not necessary because of the lack of light. Since eyes require food energy to maintain, and are very prone to injury, an eyeless cave fish can survive longer with less food than a fish that has eyes.

What the troglobites have lost they make up for with longer legs and antennae, or feelers, and with adaptations that enable them to go for long periods of time with little food. Animals that have completely adapted to cave life include: cave fish, cave crayfish, cave shrimp, isopods, amphipods, millipedes, some cave salamanders and insects.

 

A little brown bat

Michigan Department of Natural Resources

The Big Story: Bats

What animal can fly with its hands, "see" with its ears, and sleep hanging upside down? Your friendly neighborhood bat. Bats are tiny mammals that are often feared by many people. Bats are one of the most misunderstood animals. The truth is that bats are gentle, intelligent animals that are quite timid when it comes to interacting with humans.

Did you know that bats are the only true flying mammals in the world? They are one of the most numerous and diverse orders of mammals. The total world population of bats is more than ten billion. About 1,000 species are recognized. In the United States, there are over 40 species of bats working to keep mosquitoes from bugging you.

Cave bats range in size from three to five inches long, with wingspans between eight and thirteen inches. Most bats in Missouri have wingspans of less than five inches. The wing of a bat is actually a hand. (Bats are of the order Chiroptera, Latin for "hand wing.") The wing is composed of the forearm and extended "fingers" of the hand. The third, fourth, and fifth fingers, or digits, of the hand support most of the wing membrane. The thumb is a tiny hook on top of the wing. The wing membrane connects with the body, back legs, and, in most bats, encloses the tail. Cave bats weigh very little, less than an ounce.

Bats can live up to 25 years and usually have only one young each year. As with other mammals, the baby bat is born alive and is fed milk by the mother. Females often nest in large colonies. They roost in caves during the day, preferring dome shaped ceilings for safety from predators. Roosting bats hang by their feet with their wings folded around them. Bats not only roost in caves, but also in attics, towers, and other man-made structures; some species even live in trees.

Many people think that bats are dirty and carry diseases. Bats are actually clean and almost disease-free animals. And yet, people are concerned that all bats carry rabies. This misconception began over forty years ago when inadequate testing procedures found that all bats tested positive for rabies. After better testing procedures were developed, it was found that bats carry a harmless virus that gave the same reaction as the rabies virus. Unfortunately, the damage was already done and this peaceful little creature was labeled as a menace to society. However, as with all mammals, there is a possibility that a bat may contract rabies. In the United States, rabid bats are rare; less than one-half of one percent of bats carry rabies. Many more rabies cases can be attributed to dogs, cats and raccoons than to bats. As with any wild animal, a sick or injured bat should not be handled!

You are most likely to see bats swirling around a streetlight as they devour your local mosquito population. Bats are the only major predator of night-flying inects. One gray bat may eat up to 3,000 insects in a single night! In Texas, there is a colony of Mexican free-tailed bats that eats more than 250,000 pounds of insects every night!

Bats feed at night, catching insects such as moths, flying beetles, and mosquitoes. How do bats manage to steer through the darkness of night and the total blackness of caves with such ease and accuracy? They use ultrasonic sound to locate insects. Bats send a high frequency sound that bounces off objects. They hear these echoes and locate, identify, and capture moving prey while flying through the dark. This process is called echolocation. Echolocation helps them navigate through the cave in total darkness. Have you ever noticed the large ears of bats? These large ears help them hear these echoes.

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