Bats are the only true flying mammals on Earth and one of the most diverse groups of mammals. One in five mammal species is a bat. Some bats eat fruit, some pollinate flowers, others catch fish out of the water, and of course there’s the notorious vampire bat, which feeds on blood. But most bats in North America are insect eaters, and that’s a good thing for us. Some of the bugs eaten by bats are major crop pests; others, like mosquitoes, are simple nuisances but can also be carriers of disease. Bats help to keep insect populations in balance.
Bug eating bats also have an economic importance. A recent scientific paper on the economic value of bats to agriculture estimated that bats provided nontoxic pest-control services totaling $3.7 billion to $53 billion per year. This study did not even consider what the indirect costs of “replacing” bats with pesticides would be in terms of potential health and pollution threats from greater levels of toxins in the environment.
Bats provide other services to humans too, such as pollinating plants and distributing seeds, in tropical and subtropical habitats throughout the world. Some of these plants are useful to people, including a species of agave that is the source of tequila, a multimillion-dollar industry in Mexico. Bat guano has traditionally been used as fertilizer for crops in various parts of the world and is also sold commercially. However, mining of bat guano may also be harmful to cave organisms that depend on it as a source of food, and removal of guano is likely to be disruptive to bats themselves, if they are present.
Bats are nocturnal, meaning they are most active at night. During the day, bats roost in caves, under the bark of large trees and other places. One of the most unusual things about bats, besides the fact that they fly, is that they navigate in the dark and hunt their prey with echolocation, or sonar. They send out a vocal signal and listen for the sound waves to bounce back. In this manner they are able to zoom in on flying insects with laser-like accuracy. Amazingly some prey species, like certain moths, have evolved “jamming” systems that thwart the bats’ sonar.
In temperate regions of the world, insect-eating bats have to deal with the winter dearth of prey by either hibernating or migrating. All the bats that have proven susceptible to white-nose syndrome so far are hibernators. Clustering in small to truly massive groups (numbering hundreds of thousands of individual bats) is one way hibernating bats conserve energy. Another way, for female bats, is to delay pregnancy until spring. Although mating occurs in the fall, the females “store” sperm in their bodies over the winter. Fertilization then occurs in the spring, just as the new bug season is getting underway, and plentiful food for mother and the new baby (only one per year for most bat species) can be expected.
Bats may play a key role in the maintenance of some cave ecosystems by bringing in an outside energy source (their guano, or droppings) to energy-poor, lightless caves. Cave biologists think some cave creatures may be highly dependent on bat guano as a source of food, and their survival may be in jeopardy as bat populations disappear with white-nose syndrome.
For obvious reasons (being nocturnal, able to fly and favoring dark, dank holes in the ground for habitat), bats are difficult to study, and biologists know very little about most species. Even something as rudimentary as “How many bats are there?” is a hard question for scientists to answer. This scarcity of information about the basic biology of bats has been a significant impediment to effectively addressing the threat of white-nose syndrome.