For thousands of years, people all over the world have been awed, fascinated, amazed or terrified by bats. These night-flying mammals evoke strongly mixed emotions, depending on cultural traditions and degree of familiarity. In the Far East, bats are signs of good luck, long life, happiness and fertility. But in much of the Western World --particularly in North America -- mere mention of bats may inspire mystical visions of drafty castles and evil spirits.
On balance, bats seem to have been given an undeservedly bad reputation. In truth, bats are retiring, intelligent animals, important to ecosystem function and of considerable benefit to people. They are not reservoirs of rabies; they do not attack people and become entangled in their hair. They are not blind, filthy vermin, and the true vampires -- just three of some 900 species of bats -- rarely feed on human blood.
Bats are valuable to commerce, science, agriculture and natural ecosystems. In North America, they are the principal predators on night-flying insects, consuming thousands of tons annually. Bat guano is an important fertilizer in many parts of the world, and bats contribute to medical research. Even the neighborhood supermarket would not be the same without bats, which pollinate flowers and disperse seeds of many popular tropical fruits.
But old myths die hard. Bat folklore goes back many centuries. Aesop, in several of his fables, personified bats as unscrupulous liars, manipulating other animals. In their art, the ancient Mayans of Central America heralded bats as gods of darkness and the underworld. In Medieval times, mere association with bats -- intentional or not - could result in dire consequences. An unfortunate woman in France was burned at the stake after neighbors testified that crowds of bats had gathered around her house and garden. And 16th century English poet John Heywood wrote that "these creatures that fly like birds, bite like beasts, hide by day and see in the dark can surely be neither flesh, nor fowl."
Myths and misconceptions aside, bats are astonishing animals. They are the only true flying mammals. Unlike "flying" squirrels and "flying" lemurs, which merely glide, bats are capable of powered flight. And they are remarkably adept at it, surpassing in many ways even the considerable skills of birds. A bat flying at 40 miles per hour can make a right-angle turn in little more than the length of its body.
The ability to echolocate is probably the bat's most amazing characteristic, however. Using complex sonar, a bat emits ultrasonic pulses that bounce off objects in the environment and return as echoes to the bat's ears, where they are interpreted by its rapidly computing brain, allowing it to maneuver appropriately. "When you remember that an echo from a target one meter away arrives back at the bat's ears within six thousandths of a second after making the sound and bear in mind that both the bat and the target are often moving," wrote M. Brock Fenton in Just Bats, "it becomes obvious that echolocation is a sophisticated means of orientation."
All told, there are today about 900 species of bats, ranging worldwide except in extreme deserts and polar regions. Bats are divided by biologists into two groups. The Megachiroptera -- about 150 species in a single family -- are generally relatively large and usually have large eyes, small, simple ears and (with few exceptions) no ability to echolocate. They are found in the Old World tropics -- Africa, Asia, Australia and the Pacific Islands. Many of them have dog- or fox-like faces and hence are called "flying foxes." They feed mostly on fruit, pollen and nectar.
Bats in the suborder Microchiroptera -- comprising approximately 750 species -- are smaller; generally have small eyes, complex ears and the capacity to echolocate. All bats in North America -- approximately 40 species, including the 18 inhabiting Colorado -- are in this group. These "micro-bats" are found nearly worldwide, from the tropics to sub polar regions, and most of them are insectivorous.
Bats are a highly diverse group. Among orders of mammals, only rodents have more species. Comparative anatomical and biochemical evidence makes it clear that bats arose from ancestors in the order Insectivora, the group that includes modern shrews, moles and hedgehogs. Fossil and many living bats share almost identical tooth structure with shrews, a good indicator of relatedness.
The oldest fossil bats date back over 50 million years. By the time bats show up in the geological record, they already are perfectly good bats, so their actual origins doubtless are considerably earlier than the Eocene, perhaps even in the Cretaceous period (while "dinosaurs" still dominated the land). Paleobiologists speculate that some kind of gliding insectivore (probably similar in some respects to a "flying" squirrel but with shrew-like teeth) found the night air a haven safe from predators and rich in food resources. These ancient animals became fine-tuned aerial insectivores gradually, as they evolved active flight and the ability to echolocate.
Bats come in a wide variety of sizes. The smallest, Kitti's hog-nosed bat of Thailand is no larger than a bumblebee and weighs less than a penny. Colorado's western pipistrelle weighs less than a nickel. At the opposite extreme are the large, fruit-eating flying foxes of the Old World tropics, which may weigh up to a kilogram (over 2 pounds) and have a wingspan of nearly 2 meters (6 feet).
Bats have all the distinctive mammalian characteristics. They bear live young and nurture them with milk. They have hair, a tightly regulated body temperature, and a well-developed nervous system.
The front limbs of bats are modified into wings. The forearms and fingers are greatly elongated and are connected by a delicate membrane of leathery, flexible, elastic skin that serves as the flight surface. When the wings are not extended, they wrinkle into folds, allowing bats to move freely along the ground. Bats actually can crawl, hop and even swim, and some vampire bats actually alight several feet from their intended hosts -- usually livestock -- and walk the remaining distance on "all fours."
Because bats' faces are often their most distinctive characteristics, many of their common names -- including slit-faced, sword-nosed, mustached, tunnel-eared, leaf-nosed, wrinkle-faced and bulldog -- describe their appearance and identify them to family. For many of the insect-eating bats, these seemingly grotesque facial features seem to be integral adaptations that aid them in sending and receiving ultrasonic signals.
All bats have image-forming eyes. The vision of microchiropterans is generally adapted for dim light. The larger flying foxes are more dependent on visual navigation and have more sophisticated eyesight.