To the Bat Boxes!
“Has any one ever written or said one kind word for the little bat? Yet ... our little friend is protecting us by working all night long seeking and destroying one of our greatest enemies, that most malevolent of insects, the malaria mosquito. ”
– Dr. Charles Campbell, in Bats, Mosquitoes, and Dollars (1925).
At the turn of the century, Dr. Charles Campbell was a pioneer in bat research. After graduating from Tulane University in 1899, Campbell returned to his San Antonio home and set out to help treat a widespread malaria outbreak by erecting “bat houses” to attract bats, in order to stave off mosquito infestations.
Dr. Campbell spent several years perfecting the design of the houses and studying bats in their natural habitat. But later analysis indicated that the Free-Tailed bats Dr. Campbell colonized in his structures weren't the voracious eaters of mosquitoes they were thought to be. The bat houses probably didn’t contribute significantly to mosquito abatement, although at the time it was assumed they had.
Still, Dr. Campbell was right about bat beneficence in ecosystems, and insect eating habits. What they lacked in appetite for mosquitoes, they made up for in consumption of moths, which are problematic to many crops.
Today's interest in bats and bat boxes stems from global recognition of the harm of using pesticides, and subsequent interest in organic farming. It isn't a coincidence that increased use of pesticides has been shown to lead to fewer bats, which in turn creates even more insects.
Despite the large number of native species of bats on the North American continent, attracting bats can be tricky. Bats are shy. While a simple bat box on a tall pole might attract a few bats or provide refuge for those evicted from a nearby building--certainly worth the effort--getting a large colony to establish itself on a farm requires much more.
A potential colony site needs a nearby water source. Moreover, bats of many species roost in maternal colonies populated by mothers protecting and rearing their babies, who are born naked and unable to fly, and thus are vulnerable to predators and extreme temperature changes.
It can take two or more years for bats to colonize a structure, even under favorable conditions. Maternal colonies generally prefer large, stable structures such as bridges or abandoned barns and mines.
Thriving bat colonies benefit organic farmers immensely. Bats can consume more than their body weight in insects each night, and a colony of 150 bats can eat more than a million insects each year.
The presence of bats, with their echolocation calls, can also deter insects from taking up residence on a farm in the first place.
Of course, wherever humanity uses land and resources for food and shelter, some disruption of the ecosystem is unavoidable, and certain insects might proliferate. Thus the concept of “farmscaping” -- creating hospitable habitat within farms for various local species with strategic placement of insect-deterring plants. It encourages conservation, accepting the presence of indigenous animals during the cycle of growing and food production -- rather than evacuating all other creatures from farmland, or forcing them to participate in the process. An encouraging trend indeed.
Fears and Facts
- Bats have excellent vision – they're not blind.
- Bats are more closely related to humans than they are to rats and mice. Their classification, Chiroptera, means “hand-wing,” referring to the way the finger bones of bats support their wings.
- Fewer than 1% of all bats contract rabies. Those who do are quickly paralyzed, and thus an unlikely source for rabies in humans. (99% of cases of rabies in humans originate from pet dogs.)
- Twelve to fourteen insectivorous bat species can be found in Napa Valley vineyards alone, with 24 total species in the state of California.
- With some exceptions for protection of property, it is illegal to buy, sell, or possess bats in California, and illegal to poison or fumigate them. There are numerous humane bat exclusion options for homeowners with roosting bats, and property owners are discouraged from disturbing bats with young pups, between April and August.
- Bats hibernate, or migrate to warmer areas in winter to follow their food supply.
- Half the bat communities in the United States are listed as rare, threatened, or endangered.
- Threats to bats are mainly human-caused: direct killing, land development, logging, sealing off of mines, irresponsible cave tourism and vandalism, and loss of natural vegetation with accompanying loss of food sources (insects and flowering plants) for bats.
- About 70% of global fruit production depends on bats for pollination and seed dispersal.
- Crops pollinated by bats include cashews, mangoes, bananas, dates, figs and guavas. The Agave plant and the Saguaro, state cactus of Arizona, also depend upon bats for pollination. The agave is used to make agave nectar, and tequila.
Substantial references for this article come from Bat Conservation International; see http://batcon.org/
More information about farmscaping can be found through the National Sustainable Agricultural Information Service; see http://www.attra.org/