Natural communities include species that interact and have co-evolved, in some cases for millions of years. Bats are involved in the symbiotic web of many natural communities worldwide. For example, bats have co-evolved as mutualists with plants that rely on them for pollinating flowers or dispersing fruit. Many important tropical fruits, such as wild bananas, avocados, figs and mangoes, are dispersed mostly by bats. Nectar-feeding bats also are important plant mutualists. Sanborn's long-nosed bat (Leptonycteris sanbornii) is a principal pollinator of cardon, organ pipe and saguaro in the deserts of the southwestern U.S. The white, tubular flowers of these cacti "open for business" at night and are visited repeatedly by long-nosed bats, which feed on nectar and carry away pollen on their fur, cross-pollinating as they visit other flowers. Bats as pollinators and seed dispersers influence strongly the composition of many plant communities.
Bats have co-evolved with their insect prey for more than 60 million years. In temperate and tropical ecosystems, bats are the main consumers of night-flying insects. Some insects have evolved abdominal "ears," which allow them to hear the high-frequency echolocation calls of hunting bats. Hearing an approaching bat, the insect performs evasive maneuvers to avoid capture. These predator-prey interactions are a high-frequency (and high stakes) game of hide and seek, and many bats maneuver quickly enough to capture even the most evasive insects. Because bats often gather in large numbers, their impact on insect populations can be important. Without bats, insect numbers would doubtless rise significantly in some ecosystems, which could affect overall balance.
Bats are also highly important in the ecology of caves. Because deep caverns receive little or no sunlight to sustain plant life, the energy to support cave ecosystems must be delivered by animals. Because bats often use deep caverns for roost sites and may gather in large numbers, their droppings (guano) provide energy and nutrients on which other organisms such as bacteria, insects, mice, rats and even fish can survive. In fact, many entire cave ecosystems are the result of historical visits by bats, and caves without bats often are biotically impoverished.
The overall role of bats in Colorado's ecosystems is poorly understood. All bats in the state are insectivorous, but their ecological importance has not been studied rigorously. Clearly, however, the bat fauna of Colorado is diverse and therefore so probably are their interactions and importance. For example, some species are aerial insectivores and interact and compete with other nocturnal and crepuscular predators, such as nighthawks, swallows and swifts. Other bats are gleaners, picking insects off vegetation, and still other species are terrestrial predators, feeding on ground-dwelling insects and arachnids, such as spiders, hence interacting and at times perhaps competing for food with scorpions, mice and shrews.
Bat guano probably has positive effects on plant growth where colonies of bats congregate in the open, such as night roosts. Bats are also important as components of food webs and are prey for snakes, owls and other raptors, ravens, jays, raccoons, foxes and skunks.
Probably for some people the importance of bats is best understood monetarily. The economic benefits of bats reach around the globe and touch virtually all our lives in one way or another. Bats are a boon to agriculture, science and medicine. The produce section of the supermarket would be sadly lacking were it not for bats. Fruit-, pollen- and nectar-feeding bats are the most effective seed-dispersing and pollinating mammals on Earth. Many of our favorite tropical fruits and nuts -- including bananas, avocados, mangos, breadfruit, dates, figs, cloves and cashews -- are now, or were in the past, dependent on bats. In Southeast Asia, the harvest of fruit of the durian tree, which is pollinated almost exclusively by a cave-dwelling nectar-feeding bat, accounts for about $100 million in sales annually.
Many other products are derived from plants pollinated by bats, including kapok plant fibers for use in surgical bandages and life preservers, balsa lumber for crafts and designers' models, sisal fibers for rope, chicle latex for chewing gum, agave juice for tequila and carob for candy and ice cream.
In temperate regions, like the United States, insectivorous bats consume enormous quantities of harmful forest and agricultural pests. Of the big brown bat, Dr. John O. Whitaker of Indiana State University, wrote, "The 150 bats in an average Midwestern maternity colony eat in a season 38,000 cucumber beetles, 16,000 June bugs, 19,000 stinkbugs and 50,000 leafhoppers. All of these are serious pest species." Larval cucumber beetles are corn rootworms, which cost American farmers a billion dollars annually. "Destruction of 38,000 adult beetles would mean about 18 million rootworms would not have been produced." The colony of approximately 20 million free-tailed bats at Bracken Cave, Texas, eats up to a quarter-million pounds of insects in a single night. Colorado's San Luis Valley free-tailed colony consumes many tons of insects during the course of its summer visit. A bat's diminutive size -- averaging about 8 grams -- belies its voracious appetite; a single bat may consume up to 3,000 insects nightly. Mosquitoes are a common prey of a number of bats in North America.
Bat guano is also beneficial to humans, especially in less developed countries. In Thailand, it is valued as the best fertilizer available, and in the tiny region of Sarawak, Malaysia, the entire black and white pepper crop -- about a third of the world's supply -- is fertilized with bat guano.
In the U.S., bat guano was used as a source of nitrate in the production of gunpowder during the War of 1812, and Big Texas Cave was mined for guano during and after the Civil War. More than 100,000 tons of bat guano was mined for gunpowder and fertilizer from Carlsbad Caverns before they were designated as a national park, and even the Grand Canyon was mined for its guano deposits in the 1920s, the droppings transported out on an aerial tramway.
A number of characteristics -- including their longevity, disease resistance, ability to become torpid easily and sonar capabilities -- make bats useful in scientific research. For example, because some bat species seem to be resistant to rabies, they have been used in investigations of disease immunity. Because some can survive in environments that are lethal to other animals (little brown bats can survive temperature extremes of 21 degrees to 131 degrees F., and cave bats can tolerate extremely high levels of carbon dioxide), bats have been used in a variety of experiments in space biology. The sonar capabilities of bats have been used as models in the development of navigational aids for the blind and for the development of aircraft radar systems.
The wing membranes of bats are nearly transparent, highlighting the blood vessels. This has been helpful to researchers studying the effects of smoking and alcohol consumption, blood cell mechanics and tissue regeneration. In addition, bats are used in studies involving aging, contraception, artificial insemination, drug testing, vaccine development, low-temperature surgical techniques and speech pathology.