The Case for Bats

Capitol Hill Girl Scout Troop 2170 building bat houses with cookie proceeds. Photo: Emily Rand

A potential Zika virus host, the mosquito Aedes aegypti, has over-wintered on Capitol Hill since 2011. In a wonderfully ironic instance of having your mistakes come back to bite you, the Hill is home to some of the same members of Congress who left for summer recess without appropriating additional Zika research funds. Though the virus has not appeared in the Hill mosquitoes, entomologists note that this is the only known instance of the insects over-wintering north of Alabama (

Zika or not, low-lying Capitol Hill has what mosquitoes like: access to water via the Anacostia River, plus small pools of standing water (maybe in your own backyard?) in plant saucers, moist outdoor basement stairwells, or puddles made by leaky hoses. It also has moisture in the underground Metro, plus the heated tunnels around the Capitol complex. I’ve written about this microclimate before with respect to roses, which thrive on the Hill. This is another, though less desirable, example. What to do?

Don’t Shoot!

If you spray insecticide to kill mosquitoes, you are effectively killing other beneficial pollinators like caterpillars, which become butterflies or, if eaten before then, food for songbirds, who would also be poisoned. Working up the food chain, spraying for mosquitoes directly impacts the food web of the Anacostia River and unavoidably the Chesapeake Bay.

There are other pollinators that could be harmed by mosquito spraying that would like nothing better than to eat mosquitoes every night by the hundreds: bats. Lately, towns like West Hempstead, Long Island, have formally endorsed these much maligned flying mammals by installing bat houses in public parks and gardens. With the northward creep of tropical diseases like Zika, dengue, and West Nile, bats are increasingly seen as part of the mosquito solution. While for some they lack the allure of a tiger swallowtail butterfly, for others they are as cute as hamsters.

In favor of bats, not bombs, lifelong bat advocate Merlin D. Tuttle writes, “Chemical poisons kill natural mosquito predators more effectively than mosquitoes. Over time, predators such as fish, insects, and bats die out while mosquitoes develop resistance, multiplying in ever larger numbers in a losing battle often referred to as ‘the pesticide treadmill.’” (

Before signing an insecticide application contract, consider the gentler alternative – inviting bats into your yard and your life. It’s not a panacea, but as we’ve already seen, neither is spraying.

Bat Basics

Bats are small mammals that nurse their young just like other mammals. They are nocturnal and are most easily seen at dusk. Bats native to our area are very small, weighing about the same as a nickel. They hibernate in caves or abandoned mines, and in our area migrate south in winter, just like many birds. Though they have very good vision, they use their superpower of echolocation to locate prey in the dark. It is said that they can navigate around something as fine as a human hair. For more on echolocation see

One important bat trait is that they eat mosquitoes – lots of them. Reports vary, but most say that a single bat can eat 600 mosquitoes in one hour alone. That is why some local governments are encouraging them as nontoxic, pollinator-friendly, bug-eating machines.

Do they have rabies? Will they fly into your hair and bite? Sources say that one-half of one percent of all bats have rabies. This is less than other mammals. Vampire bats live in Central and South America, not here. Yes, if you see a bat in daylight, do not approach it, and keep your cat and dog current on rabies shots. But there is much to gain from developing an acquaintance with bats.

Bats on the Hill

You may already have bats roosting in your tall trees. Check your yard at dusk and see if you observe any. There may be up to 10 different species in our area. We are better at identifying birds than we are bats, but it’s something to aspire to. Congressional Cemetery Executive Director Paul Williams confirms that the cemetery has quite a few. Williams says, “They roost in the tall trees on our 35-acre property and we see them quite late into the fall,” adding, “it seems appropriate to have them in the cemetery.”

Frager’s Garden Center manager Kristen Sampson has unpainted cedar bat houses for sale made by Audubon. “They should be installed at least eight feet high, and facing south or east,” she says. The bats “need a clear flight path into the bat house, which can be tricky for some Hill homes.” If you install a bat house and nothing happens after a year, try moving it to a new location. Ginkgo Gardens also sells bat houses and will give you advice when you go. Although it’s September, it’s not too late to try a bat house at your place. Shop local so you can share your stories and help others learn.

Architect and Capitol Hill resident Jon Penndorf has observed bats from Australia to Austin, plus a cool exhibit at the Baltimore Aquarium which he highly recommends. He was disappointed when the National Zoo closed its bat exhibit. His daughter Maggie is a member of Girl Scout troop 2170 (the Zika patrol) that recently embarked on a bat house building project. Says Hill bat enthusiast Emily Rand, “the girls of Girl Scout troop 2170 (the Zika patrol) voted to use some of their Girl Scout cookie earnings to buy the materials so that they could make bat houses. Then in early May, as an activity during one of the normal Thursday-evening meetings, the girls gathered in the basement of the Liberty Baptist Church, which graciously lets the troop meet in their basement. Each of the girls got some precut wood, a hammer, and nails. After a brief instruction they started putting together their own bat houses.” We have not yet heard whether these bat houses are occupied, but perhaps now that the school year is starting we will receive some positive reports.

Bats Like Flowers Too

Remember, bats are pollinators and they are nocturnal, so this means planting evening or night-blooming flowers to attract them. One friend’s mother always plants moonflowers for her bats. Other good options include evening primrose, phlox, Nicotiana, and four o’clocks.

Wanted: Batman

You don’t research bats long before running into the name Merlin D. Tuttle. This man has done for bats what Jane Goodall did for primates. And now the international NGO he founded, Bat Conservation International (BCI), is searching for a new executive director for its staff of 28. Bat lovers, nonprofit execs, environmentalists – this could be your next DC gig! See the listing at But if your bat aspirations are more modest, check out BCI’s helpful hints about bat house building and installation:

If you have a bat story to share, please let us know!

Locally purchased bat house newly installed in Capitol Hill alley. Photo: Cheryl Corson
Lots of good reasons to be kind to bats. Image: Bat Conservation International.

Cheryl Corson is a licensed landscape architect and writer practicing on Capitol Hill and beyond. For design assistance see

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