Pest-Predator & Pollinator
Reflections on California’s Beneficial Bats
by D. R. Darvishian
A Canyon bat
And how bewildered is any
womb-born creature that has to fly.
As if terrified and fleeing from itself,
it zigzags the air, the way a crack runs
through a teacup. So the bat quivers
across the porcelain of evening.
– Rainer Maria Rilke (1923)
Forever. That’s approximately how long bats have been taking it on their often wrinkled, pug-nosed, leaf-shaped little snouts. Bats, reads the cultural record, have been so maligned for so long in the West that Rilke’s elegant stanza above can be thought of as kind—an interspecies epiphany. A clarifying moment between mammals, one way or the other.
For millennia, bats quivered around in the night as enigmas. No one knew quite where they belonged among the animals. They flew like birds, and in some places they were considered to be. It was only in the late 18th century that they were classified taxonomically, placed into the order Chiroptera, meaning “hand wing” in Greek.
Rilke, at least, understood that bats have nipples and navels and suckle their young. In fact, bats have nurseries and lick their pups clean, like the family retriever. Unlike dogs, though, bats would do just fine without people. Yet while bats may not be our best friends, they’re one our greatest agricultural heroes and do us all kinds of good.
From insect control and plant pollination to seed dispersal in the Southern Hemisphere—where without them rain forests might never regenerate—bats provide irreplaceable benefits. One estimate asserts that, across the nation, insectivorous bats save farmers nearly $4 billion a year in crop loss and reduce pesticide bills. According to the U.S. Department of the Interior, over 300 species of fruit depend on bats for reproduction, while in warmer climates, bats pollinate fruit trees like bananas, mangoes, and guavas. And you might want to thank them for your next margarita—without the bats pollinating the blue agave plant, the source of tequila would not have survived its first season.
In Northern California, bats consume millions of insects each night, spring through autumn, including vast numbers of mosquitoes. State officials worry about the introduction of West Nile virus, as well as other “highly virulent mosquitoborne viruses,” yet bats eat the irritating bugs that carry them without harm. California itself is a bat bastion. With its long, temperate coastline and varied landscapes, the state hosts 25 bat species—more than half of the 47 species living throughout North America, all of them nocturnal. Most people would be lucky to glimpse just a few. Bats naturally have favorite habitats, so any dedicated bat spotter should be prepared for a lot of night hiking.
Evidence indicates that people have been bat-curious and telling tales about them for thousands of years. In some places bats embody a deity, in others they may bring good luck or bad, and in yet others, they are cunning, mystical creatures. Bat images were found in Egyptian tombs dating from 2000 BCE. In Zuni fetish tradition, Bat is guardian of the night. In Cameroon, Africa, bats have allegedly sucked the life out of sleeping adults, and tales from Sierra Leone have children suffering exsanguination by hammer-headed fruit bats. Urban folks rarely see them in real life, often rooting their understanding of the creatures in the legends and myths that have developed around them over the years.
In Aesop’s Fables, there is a story about a great war between the world’s birds and beasts, featuring bats—who were neither—as duplicitous schemers who changed sides when battlefield fortunes waned for their allies. They were freelancing, but when both sides finally noticed, bats were banished into the night. After that, “neither the birds nor the beasts would have anything to do with so double-faced a traitor, and so he remains to this day a solitary outcast from both.”
In a more modern-day defense of the winged creature, Canadian author Kenneth Oppel employed Aesop’s yarn to see things from the bats’ perspective after the war. His award-winning Silverwing novel series follows the often harrowing adventures of Shade, a Silverwing bat, from his life as a newborn colony runt through adulthood, using their banishment to propel Shade’s quest for his day in the sun.
Superstition and folk tales aside, bats go back more than 52 million years, judging by the oldest known bat fossil. Discovered within an ancient Wyoming lakebed, the bones look remarkably similar to those of modern bats. The finding astonished some researchers. “The very first fossils of bats were bats that are already bats,” paleontologist Tim Rietbergen of the Naturalis Biodiversity Center in Leiden, Netherlands, told Smithsonian magazine (April 2023).
For generations, it has been thought that bats are attracted to human hair. Not true, notes Mary Jean “Corky” Quirk, director of NorCal Bats in Davis, a group focused on bat education and rescue. She has known of cases where bats that are busy feeding—say, pursuing moths gathered around a parking lot light—can get tiny claws tangled in the hair or clothing of human observers. While such moments can be hypertensive for all concerned, Corky counsels calm … or as much of it as can mustered. Bats are pretty adept at extricating themselves and are likely to fly off without assistance.
Since all North American bats are nocturnal, finding one on the ground during the day may be a sign that the animal is sick or injured. Any potential Good Samaritan would be well-advised to find a pair of sturdy gloves before lending a hand. Norcalbats.org offers other advice on handling bats safely. But once the critter is secured, what next?
NorCal Bats is one of the few bat rescue outfits in Northern California, and they often help by activating their informal network of bat enthusiasts. To handle bats professionally requires certification, but anyone can transport a bat to safety. “We’ll often meet a person halfway and make the transfer,” said Quirk. “We deal with injured bats, which are quite often hurt by cats, but I get calls about crows and ravens. We can usually offer advice. I’m one of those people who will get out of my car to move a dead squirrel off the road, so the turkey vulture swooping down for a meal doesn’t get clobbered, too.”
Although California’s bat population appears stable, bats elsewhere—mainly in the eastern U.S. and Canada—have died in the millions, killed by a cold-loving fungus that causes white-nose syndrome (WNS), characterized by its color and fuzzy appearance around the muzzles of hibernating bats. First encountered in 2006 in upstate New York, the fungus seems to have been transported accidentally from Eurasia. It has been traveling, likely on the gear of unwitting sport cavers, and is assumed to have made its way to northeastern California based on amplified testing.
Globally, the biggest threat to bats is habitat destruction, said Frick. Homes and roads built too close to roosts; people entering maternity caves, where mothers care for their pups until they can fly on their own; runoff water clogging or polluting cave streams; wanton destruction by vandals—all of these actions, and others, including uninformed cavers spreading disease—can drastically affect bats. The over-harvesting of bat guano, used as fertilizer by many Northern California growers, can alter cave environments irrevocably. Guidelines for guano mining have been promulgated by the likes of the International Union for Conservation of Nature, but acceptance has been slow.
As climate change heats up our summers and brings heavier rains, mosquito season will last longer, and our alliance with bats will become even more important. Quirk says people can make their properties more bat-friendly by “reducing or not using pesticides, supporting farmers that use integrated pest management or grow organic crops, and planting native plants, especially those that bloom at night to support the native insects.“ You can also provide bats with some excellent accommodations in the form of bat houses (see sidebar). Keeping these winged mammals happy and healthy preserves balance in the ecosystem, as well as the opportunity to witness their balletic hunting flights before a backdrop of stars on summer evenings.
Installing a Bat House
Mounting a bat house on your property is the perfect way to help bats who are in need of a safe place to live while protecting your yard from pesky night-flying insects.
It is also a great way to get involved in bat conservation. Habitat loss is a major problem for bats, and putting up a bat house can give your local bats a safe and comfortable place to live.
The invaluable online resource, NorCalBats.org, is home to the NorCal Bats organization that is devoted to bat education and rescue. It has plans for how to build your own bat house and links to purchasing one if you’d rather do that. It also includes these important tips for how to install that bat house once you’re ready.
Bat houses should be mounted on buildings or other large wooden or concrete structures.
It is best to install bat houses at least 12’ from the ground (15’ to 20’ is better). Bats don’t want to be too close to the ground, and predators.
Bat houses should receive at least six hours of daily sun exposure. Generally we recommend that it be mounted facing east, to get the morning sun, but south works also. You are trying to maximize the amount of time that the box temperature is between 80°F and 100°F.
Mounting on a pole may work well in climates that are moderate to hot, without extreme temperature variance. We find that they don’t get occupied as often as bat houses on a building (properly located). If you do mount on a pole, it may work best if you have two bat houses mounted back to back to increase temperature retention.
Avoid mounting a bat house in trees. In California, we rarely see bats occupy a bat house mounted in a tree. It is too easy for predators to access the box. Aim for 20’ to 30’ from the nearest tree if possible.
Don’t let wasp nests accumulate. If they do, they should be removed in late winter or early spring before either wasps or bats return.
If you are installing a bat house on a farm or other large property, it works best if it can be placed within a quarter mile of a permanent water source, such a canal, pond, or stream.
Bat houses in warmer areas, such as the Central Valley, can sometimes overheat, and pups may fall out due to stress or overcrowding. Consider adding a bat house pup catcher. This would be a nylon mesh pouch that you would mount at least 24 inches below the opening in the bat house. Fallen bat pups will be able to crawl back to the bat house if you build the catcher properly. Note that you may have to clean guano out of the pouch periodically.
Be patient—it can take several years before bats decide to move in. But if you don’t have any occupants after 3 years, you might consider moving the bat house to another location/ orientation.
More information is available at NorCalBats.org.
D.R. Darvishian is a longtime writer, journalist, and editor living in Lakeport, CA, and now sees bats in his dreams.
Bat cover photo by U.S. Fish and Wildlife Service Headquarters, Public domain, via Wikimedia Commons. Article Bat photo by Bob Johnson, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons.