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Bug Eating Bats?
Question. Mike: As you know, it's flatas a pancake down here in Delaware. There are a lot of marshy areas andlow spots that hold water where I live, mosquitoes are a big problem,and I would like to attract bats to the area. I already have three bathouses up on trees that get lots of sun; two are 20 feet high and Imanaged to get the other one 40 feet up. I would like to get a headstart on making sure they get occupied before the skeeters arrive thisspring. Any suggestions on how I can attract the little brown mammals?
            ---Yourdedicated bug bitten listener, Kurt in Seaford, Delaware

Seaford—the nylon capital of the world! Well, this is another of thoseseemingly simple questions whose surprising answer is going to rock alot of worlds. Everybody sitting down out there? Good. Because whilebats do eat some mosquitoes, it isn't enough that you'd notice anylevel of control.  

That's the bombshell dropped by respected bat-expert Dr. Tom Kunz,Professor of Biology and Director of the Center for Ecology andConservation Biology at Boston University, where the Kunz Bat Lab( named in his honor. Involved with thefabulous flying mammals professionally for over 40 years, Dr. Kunzexplains that popular notions of bats eating hundreds of skeeters anhour are hyperbolic extrapolations of a 1960s study that used fruitflies—not mosquitoes—in a laboratory setting.

Studies of bats in the wild have revealed that mosquitoes make up avery small part of their diet; 10% or less. Which only makessense—mosquitoes are small and take a lot of energy to catch; muchbetter to devour a big tasty moth and get the same amount of protein itwould take dozens of skeeters to provide.

But Dr. Kunz is quick to point out that this doesn't change the bats'beneficial reputation one bit. In fact, the wonderful reality of theirmenu makes a discussion of bat attraction much more germane to thishere show; because, instead of the erroneously rumored mosquitomajority, the bats' most common victims are agricultural pests.

Bats consume night-flying moths that would otherwise give birth todestructive pest caterpillars like the cornearworm; cucumberand potatobeetles; and swarms of flying ants and termites. And the littlebrown bat—the most common bat in North America—does prey on a differentsummertime biting pest: Midges like the notorious "no see ums". Andthese bats do live up to the appetite part of their reputation,consuming half their body weight in insects in a single evening; all oftheir weight if the bat in question is nursing. So they are good.They're just not good for EXACTLY what we thought.

If nearby water is brackish or salty, it will restrict your ability toattract the night-flying insect eaters, warns Dr. Kunz, who explainsthat bats require fresh water to drink. If it isn't availablenaturally, you'll need to put out a cattle trough-sized water source tokeep them happy. Or a swimming pool; bats love swimming pools, he notes.

They also need a place to roost. Bathouses CAN be helpful, says Dr. Kunz, but a lot of the ones outthere are just too small. As this week's questioner has already noted,houses should be exposed to the sun because bats like it warm. But abat house IN full sun can really cook on a hot summer day, and theremust be adequate room for the bats to move up and down to regulatetheir body temperature—up when its too chilly and down when its toohot. (Apparently Goldilocks had some bat in her.) The minimum height toallow this movement is 30 inches, but taller is always better.

Barbara French, a biologist for Bat Conservation International, addsthat placement on trees can be counterproductive if there are branchesbelow the bat house. "The bats have to be able to drop freely out ofthe bottom of the box; if there's any obstruction below, they won't useit." Nailing a box to a tree also makes it difficult to installpredator guards. That's why she and Dr. Kunz prefer poles. They insurea 'free drop' for exiting bats and it's easier to install aluminumguards to keep cats, raccoons and such out.


You Bet Your Garden   Question of the Week  ©2006Mike McGrath