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Question. Mike: As you know, it's flat as a pancake down here in Delaware. There are a lot of marshy areas and low 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 bat houses up on trees that get lots of sun; two are 20 feet high and I managed to get the other one 40 feet up. I would like to get a head start on making sure they get occupied before the skeeters arrive this spring. Any suggestions on how I can attract the little brown mammals?
---Your dedicated bug bitten listener, Kurt in Seaford, Delaware
Seaford—the nylon capital of the world! Well, this is another of those seemingly simple questions whose surprising answer is going to rock alot of worlds. Everybody sitting down out there? Good. Because while bats do eat some mosquitoes, it isn't enough that you'd notice any level of control.
That's the bombshell dropped by respected bat-expert Dr. Tom Kunz,Professor of Biology and Director of the Center for Ecology and Conservation Biology at Boston University, where the Kunz Bat Lab(http://www.bu.edu/cecb/BATS/)is named in his honor. Involved with the fabulous flying mammals professionally for over 40 years, Dr. Kunz explains that popular notions of bats eating hundreds of skeeters an hour are hyperbolic extrapolations of a 1960s study that used fruit flies—not mosquitoes—in a laboratory setting.
Studies of bats in the wild have revealed that mosquitoes make up a very small part of their diet; 10% or less. Which only makes sense—mosquitoes are small and take a lot of energy to catch; much better to devour a big tasty moth and get the same amount of protein it would 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 their menu makes a discussion of bat attraction much more germane to this here show; because, instead of the erroneously rumored mosquito majority, the bats' most common victims are agricultural pests.
Bats consume night-flying moths that would otherwise give birth to destructive pest caterpillars like the corn earworm; cucumber and potato beetles; and swarms of flying ants and termites. And the little brown bat—the most common bat in North America—does prey on a different summertime biting pest: Midges like the notorious "no see ums". And these bats do live up to the appetite part of their reputation,consuming half their body weight in insects in a single evening; all of their 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 to attract the night-flying insect eaters, warns Dr. Kunz, who explains that bats require fresh water to drink. If it isn't available naturally, you'll need to put out a cattle trough-sized water source to keep them happy. Or a swimming pool; bats love swimming pools, he notes.
They also need a place to roost. Bat houses CAN be helpful, says Dr. Kunz, but a lot of the ones out there 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 a bat house IN full sun can really cook on a hot summer day, and there must be adequate room for the bats to move up and down to regulate their body temperature—up when its too chilly and down when its too hot. (Apparently Goldilocks had some bat in her.) The minimum height to allow this movement is 30 inches, but taller is always better.
Barbara French, a biologist for Bat Conservation International, adds that placement on trees can be counterproductive if there are branches below the bat house. "The bats have to be able to drop freely out of the bottom of the box; if there's any obstruction below, they won't use it." Nailing a box to a tree also makes it difficult to install predator guards. That's why she and Dr. Kunz prefer poles. They insure a 'free drop' for exiting bats and it's easier to install aluminum guards to keep cats, raccoons and such out.
And a 'box' is not the best design, notes Dr, Kunz. Really successful bat chateaus are often closer in shape to a purple martin house—like the small shed he erected on poles for a colony being evicted from an old blacksmith's shop that was being torn down; it's currently home to a thousand bats! And always leave dead or dying trees in place whenever possible; bats love living in the hollow sections of these 'snags'.
In relatively cool climates, bat houses should be black to absorb heat;in warmer climes, white to reflect the heat. You must keep the area around the house dark at night, but you can use a light where you want the bats to feed—the light will attract bugs, which will attract the bats. A light over a big source of fresh water would be the Bee's Knees.
There are other factors to consider, of course—the interior wood surfaces of bat houses should be roughened up, for instance. Bat Conservation International (www.batcon.org) has a list of approved pre-built houses and plans to build your own. And successful occupancy will be obvious, says Dr. Kunz; you'll see bats flying out of the house at dusk, and their droppings will be visible below.
Hey—a great place to put your compost pile!
You Bet Your Garden Question of the Week ©2006Mike McGrath