Bats

Bats in the garden? Let’s hope so!

While bats can be vectors for diseases, such as rabies, more often than not, bats are a gardener’s friend. In just one afternoon, you and your kids can build a bat box that just might attract these garden predators for many years to come.

Commerson’s leaf-nosed bats (James J Sharp) CC BY-SA 3.0

It is estimated that a pregnant or nursing bat will consume 2/3 of their body weight in insects each night. According to UC Division of Agriculture and Natural Resources (UCANR), bats protect over $23 billion of American crops each year. That’s a substantial impact for a flying mammal that weighs in around 1/3 of an ounce!

​A little bat history

Bats started flying around over 50 million years ago, after the dinosaurs died off, but we know surprisingly little about them. One thing we do know is that their numbers are in serious decline. According to the U.S. Forest Service, “Currently 56% of the bat species present in North America are listed or being considered for listing under the Endangered Species Act.” Loss of habitat and human prejudice are mostly to blame.

Vampires!​

Contrary to popular myth, most bats are not vampires. Vampire bats are only found in Latin America and they prefer the blood of animals to that of humans. Most bats are insectivores. The rest of them eat fruit, mice, or other small mammals. These fruit eaters are frequently considered a “keystone” species. This means that the plants which rely upon bats for pollination and seed dispersal are critical to the survival of other animals and birds. Bats are the major pollinators of agave. You know, the stuff used to make tequila. And the Mexican Free-tailed bat is responsible for pollinating most of the sugarcane used to make a well known brand of rum.  [Take a closer look at the label and you will see the bat!]

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Many years ago, while volunteering at Woodland Park Zoo in Seattle, I worked with fruit bats in the Nocturnal House. Larger than our native bats, the zoo’s fruit bats were sweet-tempered, gentle, and loved being scratched around the face and ears. Not what you expected, right?

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Little brown bat (Andy Reago & Chrissy McClarren) CC BY 2.0

Bat species

Scientists are still debating bat classification. One camp believes that all bats evolved from a single mammalian flying ancestor. Others classify bats into two groups: megabats and microbats. Megabats are found in Asia, Australia, Africa and the South Pacific. The largest megabat species has a 5’6” wingspan! This group evolved from lemur-like animals and they do not have the gift of echolocation. Microbats are found everywhere except Antarctica and are believed to have evolved from shrew-like animals. Microbats do use echolocation to navigate. All bats have an excellent sense of smell. Worldwide, there are 925 bat species. I tracked down three major bat families in North America:

• Leaf-nosed bats (Phyllostomidae)
• Plain-nosed, or little brown bats (Vespertilionidae)
• Free-tailed bats (Molossidae)

The most common bats found in gardens include:

• Big brown bat (Eptesicus fuscus) - longish brown fur, 4 to 5” body; 12” wingspan
• Yuma myotis (Myotis yumanensis) - pale brown, tan, or gray fur; 9” wingspan
• Little brown bat (Myotis lucifugus) - glossy brown above, gray underneath; 3” body; 9” wingspan
• Mexican Free-tailed bat (Tadarida brasiliensis)- dark brown to gray; long-tailed; 3.5” body; 11” wingspan
• Western red bat - reddish brown fur; has lost 95% of its breeding ground
• Townsend’s big-eared bat - 4” body; 11” wingspan; long, pointed ears; frequently abandons its young when disturbed by humans

Benefits of bats

All bats in the Bay Area are insectivores. A single bat can consume hundreds of insects in an hour and they may live for 5 to 30 years, depending on the species. While research has shown that bats do not have a significant impact on mosquito populations, they do help control beetles, moths and moth larvae, wasps, ants, and cockroaches.

Bat lifecycle

Bats generally mate in fall, but females hold onto the sperm for several months, until conditions are more favorable for their young. Then conception occurs. A single pup is born each year around May or June, blind and hairless. The pup is diligently cared for until it learns to fly after a month or two. Young bats will try to eat pretty much anything. Unfortunately, they do not like banana slugs. Like dolphins, microbats are believed to use the Earth’s magnetic field to find their way. Many microbat species migrate over 1,000 miles each year, the same way salmon do, returning to their place of birth. 

Residential bats

Each year, many bat pups starve to death when humans try blocking bats from entering, not realizing that the young are already inside. Result, less bats in the world and dead bats in your attic. If you really must get rid of bats, hire a professional. A better choice would be to build your own bat house and lure your guests away from your home while taking advantage of their voracious appetite for garden pests. That being said, bats can carry diseases that are dangerous to humans, so wild bats should NEVER be handled. This is for your safety and theirs.

How to build a bat box

Bat boxes are simple to make. Since bats prefer tight, skinny spaces, a bat box is, for the most part, several sheets of wood separated by thin boards. To make the most out of your bat house, be sure to avoid these common problems:

• Do not use pressure treated or repurposed wood that may contain chemicals
• Be sure your bat box has multiple chambers
• The interior must have rough edges or grooves the bats can hang onto
• Durable roofing will protect the bats and the bat house
• Use caulk on all seams to prevent warping and drafts
• Protect the exterior with paint or some other sealant, to prevent warping
• Use a tall, open-bottom design
• Place the bat house where it will get 7 hours of morning sun and afternoon shade each day
• Bat houses should be placed at least 10' in the air
• Be sure to provide a water source
• Watch for hornet invasions
• Be sure the design includes a landing plate
• Keep the bat house away from fire pits, air conditioners, high traffic areas 

Bat Conservation International has the best bat house plans I have seen. When placing your bat house, keep in mind that those hung on poles or in trees are almost never used because they get too cold at night, or opossums and raccoons will eat the bats. Chimneys work well, but then there’s the issue of guano (bat poop) accumulation. Guano should never be handled without skin and respiratory protection. Guano may contain lots of nitrogen, phosphate, and potassium, like most fertilizers, but it can also make you really sick. It is used to make gunpowder…