No need to fear the bat, the gardener’s friend

Mysterious winged creatures of the night known to inhabit spooky old barns and buildings, bats are as much a symbol of Halloween as witches, skeletons, ghosts and, of course, vampires.

Their preference for night hunting and roosting in dark and decrepit places and caves made them an object of mistrust in more primitive times. Images of Satan often feature a devil with batlike wings rather than the birdlike ones of angels.

But the poor bat has gotten a bad rap. Far from menacing, these flying mammals, many as small as a mouse, are actually good neighbors, dining on many of the insects that go after food crops.

“Bats provide pest control on farms. In our area of North America they only feed on insects, and a lot of insects they feed on are crop pests like the codling moth that goes after apples and pears,” said Rachael Long, a bat expert and farm adviser with the University of California Cooperative Extension Service.

One study by the U.S. Geological Survey found that bats save the agricultural industry from $3.7 billion to $53 billion a year in pest-control services.

It’s not unusual to see bat houses set up near vineyards to entice bats to protect the North Coast’s valuable wine grapes. But the flying furry critters are also good for the garden, dining on pests like stinkbugs and horned worms that go after your tomatoes.

Long, who is based in Woodland but does bat education work in counties that include Sonoma, said bats eat full-grown moths, and, by eating the adults, they’re cutting down on the population of voracious larvae.

“They do eat a lot of pests that are found in our gardens as well. They go after tomato fruit worms, also known as corn ear worms, and cucumber beetles that have a green shell with black spots. They’re an awful pest that will take down seedlings to nothing. Roses are affected by cucumber beetles,” Long said.

Bats eat at least half their body weight in insects every night.

One way to attract bats to your property is by offering them a warm and safe place to roost. Bat boxes or houses can be purchased ready-made at places like Tractor Supply Co. Bat Conservation International (Batcon.org) has quality information about installing boxes and a link to purchasing plans for DIYers.

Rick Wood of Napa Valley Products Service and Industry, or PSI, makes a bat house with Bat Conservation International’s seal of approval. It is about 28 by 20 inches and capable of accommodating a colony of 50 to 75. Bats enter through a one-inch slat in the bottom, catching onto mesh installed in the bottom and then pulling themselves inside.

He recommends mounting the boxes on flat, vertical surfaces like the side of a barn or shed, at least 12 feet off the ground. Two can be mounted on a wood or metal post, but should be free from nearby obstacles. In warmer areas of the North Coast, they should face south so they catch morning sun and afternoon shade.

You also want to put them where they will be used. Bats spurn boxes placed in trees, and Long learned the hard way not to put them on the side of your house.

“When they go in and out of the house, they defecate and urinate, and will leave streams of guano and urine all up and down your wall. It’s going to be messy and smell,” said Long.

If you don’t have a good place, ask a neighbor with a shed or barn if they would be willing to install one. Bats will travel up a mile from their roost to forage, Long said.

Other experts have more recommendations. Greg Tatarian, who owns the private consulting firm Wild Research Associates in Santa Rosa, said bats really need a larger foraging area, minimally two to three acres. And they tend to stick to their roost for a long time, so don’t install a box if you plan to sell your property within a few years. Losing their home can be extremely stressful to them, he said.

If you think you are seeing more bats at this time of year, it’s not a figment of your Halloween-steeped imagination.

Many bats are migratory. Intolerant of cold, they head south to warmer climates when temperatures drop.

“A lot of the calls I get are from people who said they just had bats show up in their barn or near their house,” said Long. It doesn’t mean you’re suddenly infested. Bats may migrate up to 1,000 miles, so they’re often just taking a rest before hitting the skies again.

“People panic and go, ‘Oh my God.’ But if you just leave them alone, usually one or two weeks, they go on to where they’re overwintering,” he said. “It’s really a wonderful time of year for bats.”

Long has written “The Black Rock Desert Trilogy,” a series of children’s books featuring a bat heroine. Throughout the chapter books, kids learn fascinating bat facts like how they navigate in the dark using echolocation.

California has 26 species of bats, including the Brazilian free-tailed bat (also known as the Mexican bat), with brown fur and square ears; the pallid bat, with big pale ears; and the California and Yuma myotis. But the population of bats is dwindling, largely due to habitat loss; two-thirds of Northern California’s bat species are in trouble.

They can live up to 30 years, but they are not prolific with reproduction. Bats typically have just one baby, or pup, per year.

While you don’t want them in your house or attic, they are usually harmless if they inhabit a shed, barn or other old outbuilding.

Like other wildlife, bats can carry rabies, so you don’t want to touch them or pick one up. Exerts recommend approaching them with caution and common sense. According to the Centers for Disease Control, bats are the most common source of human rabies in the U.S., although the odds of contracting rabies is slim. Only one or two human cases are reported each year.

So what should you do if you suspect you’re sharing your own home with bats?

For the rare bat that winds up inside, Long recommends turning off the lights and opening the door so it can exit on its own.

Or prevent that from happening by keeping doors and windows closed and making sure screens are intact and tight. Seal and caulk the house and replace missing pieces of metal or wood.

If you suspect bats are in your attic, ceiling or walls, call a trained wildlife exclusion expert to set up humane, one-way exists, through which they can get out but can’t get back in. Simply sealing them in can lead to a terrible, smelly mess when they die. It can take four to seven days for an entire colony to exit.

Bats are sensitive to cold, so late fall and winter are cruel times to cast them out. Tatarian said it’s better to wait. Also avoid exclusion efforts during the birthing season from April to August.

You can reach Staff Writer Meg McConahey at meg.mcconahey@pressdemocrat.com or 707-521-5204. On Twitter @megmcconahey.