Bats common and beneficial in Contra Costa

By James Hale:                                     

With the recent report of a death from rabies caused by contact with a rabid bat in southern Contra Costa county, we asked James Hale to give us some background and information on bats and their various species, and to also remind readers that all wildlife should be left untouched when found.

Bats are one of our most misunderstood animals. They are thought to be mysterious creatures of the night, souls of the dead, and blind, rabid creatures that commonly become entangled in peoples’ hair. In fact, bats are an extremely beneficial wildlife species whose considerable collective consumption of night-flying insects results in fewer agricultural pests and annoying mosquitoes. Bats have been flying mammals for perhaps 60 million years or more and are highly specialized in both physiological structure and behavior. The power of flight allows some species to avoid inclement weather by migrating to more favorable conditions.

In Babylonia bats represented the souls of the dead. In China they were symbols for happiness and long life. To the ancient Mayans, they were symbols of initiation and rebirth. To the medieval peoples, they were miniature dragons. Native Americans believe the bat is powerful medicine, always indicating initiation – a new beginning that brings promise and power after the changes.

From a naturalistic view, bats are not sinister. They play a valuable role in nature. Most bats feed on insects, with the fruit and nectar-feeding bats being essential to the pollination of many plants.

Their waste product, guano, is also used as a valuable fertilizer. The high nitrogen content of guano made it useful in the manufacture of gun powder. Contrary to popular belief, a University of Calgary study of bats in North America, shows that the percentage of bats that are rabid, regardless of species or where the bats roost, is less than one half of 1%.

Individuals of some bat species can capture 500 – 1,000 mosquitoes in a single hour, with large colonies consuming tremendous quantities. For example, a Florida colony of 30,000 southeastern bats consumes 50 tons of insects annually. Approximately 80% of Little Brown Bats living in the northern United States and Canada eat mosquitoes. Worldwide other bats are adapted to feed on fish, frogs and other resources. The Vampire Bat of Central America, a bat responsible for many of the misconceptions, laps blood from their host after making small incisions to a blood vessel.

There are about 850 species of bats worldwide, almost one quarter of all mammals on the planet. Thirty-nine species occur in the United States with 25 found in California. They are second only to rodents in both diversity and number of individuals. Weighing less than 2 grams, the smallest bat is the Bumblebee Bat from Southeast Asia, about the size of a large bumblebee. The largest is the frugivorous Flying Fox of Australia, Africa and other regions, weighing up to 3.5 pounds with a wingspan of almost 6 feet.

The animal’s wing consists of double layers of skin stretched across the modified bones of the fingers and back to the legs. They generate lift by pushing their wings against the airs resistance, so they tend to have large wing surface areas for their body size. Bats’ knees bend backward, unlike any other mammal, which allows them to roost upside down and capture aerial prey with their tail membranes.

All bats have good vision, however their crepuscular and nocturnal habits have led to an increased dependence upon their sense of hearing. By emitting high – pitched sound, which bounces off of objects including aerial prey, they use echolocation to navigate in the dark. Their ears are large and well developed to receive and determine an echo’s location. Locally, the Pallid Bat feeds largely on flightless insects, which it captures by foraging on the ground. Jerusalem crickets, scorpions and June beetles figure largely in the diet of this bat.

Habitat destruction, disturbance to roosting sites in caves and mines and the recent discovery of a fungal infection pose serious threats in North America. The White Nose Syndrome (WNS) is a poorly understood disease associated with the death of at least 6.5 million North American bats. The condition, named for a distinctive white fungal growth (Geomyces destructans) around the muzzles and wings of hibernating bats was first identified in New York in February 2006. It has spread rapidly with no obvious treatment or means of preventing transmission.

For more information on bat conservation : , or

James M. Hale is a wildlife biologist and member of the Contra Costa County Fish and Wildlife Committee