The other evening, I decided to put on boots and walk down the driveway to commune with my brand new wildflower planting at the bottom of our driveway. Twilight was descending, a flush of pink still highlighting the eastern sky, and the crickets were pitching a cocophany through the trees as I walked. Our driveway is a little steep, but a lovely stroll in the cool shade of tall trees flanking its sides. As you descend below the fern line, ferns arch out from the banks (mostly our native Christmas fern, Polystichum acrostichoides), and a birch stand spills down the steep hillside to the left. I’ve grown to adore the birches (Betula lenta) with their silvery bark, their fine leaves, their proclivity for growing atop boulders (we have boulders and big quartz outcroppings around here, also cool), and how they like to march down ravines in groves, holding court like tall faintly luminous Aunties. Or Ents.
The Sweet Birches
I have been calling them beeches for years, because they don’t have that distinctive white bark of paper birches, which are further north of here. But I recently figured out that they are Betula lenta, the sweet birch. The catkins give them away, as well as their adaptability (and therefore their widespread presence in this part of the world). Like all widespread trees native to a place, their contributions to the ecosystem and to wildlife are many (wildflower.org rates their wildlife value as “very high,” and Native Plant Finder says it’s a larval host for 321 species of caterpillar, which feed the abundant birds in our woods among other things). Apparently this is very important. Larval hosts, mostly trees, do the heavy lifting when it comes to converting the sun’s energy to protein and supporting the food chain. The first step in that is an edible plant to a caterpillar!
For humans, wildflower.org also says that the sweet birch once provided the oil sold as wintergreen (now synthetically made). I just went out to take a few leaves and sniff the stems, and – it does smell just like wintergreen! So amazing. Thus the name: sweet birch! This tree is not browsed by deer, probably because of that oil, which would also explain why it is so prevalent around here.
**Update: Michael just confirmed the old timey uses of sweet birch for wintergreen oil. He went on to say that the young tender branches (not the leaves or the leaf stem, which taste nasty) can be chewed on. It’s fun for kids, he said, and when you chew on them, it gives you energy, freshens your breath, and so on. Saplings are best for this. I wish he would tell me these things before I have to go hunt them down on Google! But it’s just cool to have that additional first-hand story.
Hunting the Rich Cove
As I walked the driveway, admiring the birch trees whose presence also indicates water and which have at last helped me to recognize this strip of land as a Rich Cove Forest (more on that in the next post!), something darted in front of my face, maybe an insect. But then I saw a shape–dim brown wings spread against the twilight. Was that a bat? Then a second form darted past–definitely a bat. Then a third and a fourth! They were hunting, I realized! Out in the evening with the air so full of the moisture from recent rains, they were hunting the insects that should have been bombarding me, especially mosquitos. I called outloud in surprise and delight to the bats–I do that (as if they can understand me, note the hint of sarcasm). But I also like to do it as a way to disarm a wild creature that might be afraid of me. I use tone and body language and body energy, which I suspect more creatures can understand than most people realize. I do this with the deer too–they’re half tame anyway, but they will still startle and leap away if you come up upon them or get too close. And I’ve found that you can get them to calm down and at least stop to look at you by talking to them sweetly! As I chimed out at the bats, one bat in particular swirled around in front of me three, four, five times, and seemed to pause in his hunting to check me out. Maybe it was a she. Maybe he was curious or maybe she was acknowledging me. It felt kind of like a mutual recognition.
Later that evening, as I walked back up the driveway from my sojourn with my pollinator wildflowers, the bats were all around me in the early night air. Eventually, I realized that I could almost sense the approach of a mosquito right before a bat would swoop past. You know how you can tell when you’re right about to get stung? I had that experience repeatedly, but instead of being stung, I’d feel and just barely see a bat woosh past. It occurred to me that despite unseasonably high rains and the very damp area of our woods that I think can technically be classified as a Rich Cove Forest, we haven’t had a problem with mosquitos this year.
Now, to back up a little, I had seen a bat flying up and disappearing into the eaves of our house a time or two in April or May. Which I’d tried to ignore, because I can’t bear the thought of going to war on bats and also because they can be a real pain if they get established in your roof! Michael’s sister owns a 200 year old farmhouse with a cupola that the bats have heavily colonized for ages and it makes the house stink. The bat guano is not only stinky but can have these dangerous fungal spores that fly around in the air if you try to clean it up without biohazard equipment. So, all of this was top of Michael’s mind when I told him about the bats hunting our driveway in the evening. He said immediately, “How do we get rid of them?” Meanwhile I was dreaming of bat houses (of course)!
Bat House Dreams
I understand Michael’s knee-jerk reaction, and I don’t want a bat infestation in our house anymore than he does! But I’m feeling emboldened by my carpenter bee house successes to try to do the same with the bats. He had several half-hearted objections like: I need to do other things besides build bat houses, and it’s expensive. But when I reminded him that battling it out with bats can be not only futile but just as expensive and time-consuming as building a nice bat house would be, he calmed down a little. Plus, there are some nice pre-made options, which I’ll share later toward the end of this post. It’s a constant process with Michael and I, the push-pull between an ultra-pragmatist raised in a conservative farming mindset and an ultra-tree hugging naturalist raised as a liberal academic. We need each other but it can be a wrestling match to get to a productive outcome. Fortunately, we’re used to it. And also, I know how to measure and cut wood and I can probably do most of it myself. This plan will hopefully work because the bats haven’t become entrenched yet.
But Why a Bat House?
Why do I want to try to house bats, besides trying to deter them from roosting in our eaves? For one thing, the wonder of encountering them on the driveway in the evening and realizing what they were doing there inspired me. It was magical. For another thing, they have dramatically improved our living conditions. I can sit out on my porch for long stretches without getting eaten alive by mosquitos. This has not been true in years past, and I really appreciate it, since I am very prone to mosquito bites. Apparently, bat populations are declining and so there is also an ecological motivation for it. There is a small but growing movement of people trying to help them out by housing them. Folks are also interested in attracting the for their agricultural benefits. We don’t have those needs, but we might in the future. Anyway, I’m trying to be a friend to all creatures, which is the bottom line!
You do have to get over a certain gross-factor, especially if you can see them hanging in clusters from the bottom of the bat house. See the photo above from Merlin Tuttle’s Bat Conservation website. Even I–and I’ve always thought that bats were a little cute, even though I’m probably the only one I know who does–even I find that a little hard to look at. So, don’t look at that if you decide you want to have a bat house and that grosses you out. I’m not trying to convince anyone, but I personally would like them to stick around, and I definitely want to keep them out of our eaves. To do that, we will need to execute our plan thoughtfully, and that will include a very good bat house.
The Bat House Plan
Bats leave in the winter, according to other folks we’ve known who have bats, so we’ll build and put up the bat house this winter. We’ll also need to do a couple things to discourage them from nesting in the same site in our eaves when they return:
- fully seal up the cracks they’ve been using to crawl in
- paint the area with something to deter them (e.g. peppermint oil or menthol).
If these are the Big Brown Bat (Eptesicus fuscus), which is common in Virginia and looks about right based on what I could see in the dim light, then our house will need to be sized to suit them. According to several articles including this one, big brown bats like “chamber widths of 7/8″ to 1″. Multi-chamber houses that include a wider roosting crevice may additionally appeal to these species.” I’ve found several articles that describe the females usually nesting separately from the males, and the males often nesting solo. But sometimes the guys will nest as a group, separate but near the females. (Sounds like people). They can also get rabies–my brother will be concerned about this. But apparently the incidence of big brown bats with rabies is low, and the prevalence of humans who caught rabies from a big brown bat bite are extremely low. According to Wikipedia, during a seven year period from 1993 to 2000, there were only 24 cases in the United States, and of those, only 1 was from a big brown bat.
How to Build a Bat House
Fortunately, there’s a lot of information on building bat houses because of the whole conservation issue, and because of the fact that they can be so helpful. Here’s a cool stat: apparently the big brown bat doesn’t just eat a prodigious amount of mosquitos, but also many agricultural pests like cucumber beetles, scarab beetles, leafhoppers, and shield bugs. However, as much information as there is out there, there’s a lot of conflicting information, and not all of the DIY suggestions make 100% sense to me (mostly as relates to finishes). So these are the principles they all seem to have in common and that I’ll be following if I build and don’t buy:
Everything seems to be constructed at roughly 20-30″ tall or wide. They all need a grippable surface on the inside–you can use durable plastic mesh (see video above) or cut horizontal grooves into the wood). The the interior dimension (the depth) is quite narrow, but a little bigger for my big brown bats: around 7/8″ to 1″ deep. It’s basically like a flat cavity with a textured lining and a little sloped roof and a fairly narrow opening at the bottom to keep out predators. Like a bird house, you can mount it on a pole or on the side of a building or on a solo tree. They apparently don’t like a lot of leafy cover right in front of and around the bat house–maybe because of tree-climbing predators and also so that they can easily fly in and out of the house.
Many of the DIY articles and videos I’ve found recommend staining the interior to keep it dark so the bats can sleep during the day. But I know from personal experience that using regular woodworking stain without a clear topcoat stinks forever until it breaks down and will be offgasing toxic fumes which is not healthy to a growing bat. So I will not be using woodworking stain on the interior or exterior of my bat house. Some folks recommend a white exterior finish to keep the house cool, others recommend a dark exterior color to keep the bats warm. I suspect these differences reflect differences in climate and I plan to leave my wood unfinished, and handle those heat management locations by picking a location possibly with part shade. But if I darken the interior finish, I’ll use exterior grade latex paint or an exterior grade stain like deck stain or siding stain (and let it cure thoroughly) so it won’t break down and off-gas so readily. I definitely would not recommend using regular woodworking stain on the exterior, because it will fade and be dusty after a year. Thinking about interior finishes, I just can’t help but imagine them scrabbling around and pooping on it and creating a toxic mess through the chemical interaction between that finish and the caustic excrement. Hopefully it just falls out the bottom…
Ooh! If I put my bat house over my garden, I’ll get free fertilizer! Or maybe over my compost pile, so it’s not a gross unsanitary mess on my garden. Imagine bat poop on your lettuce–no! Actually, the bat conservationist Merlin Tuttle whose article I’ve linked to gave an interview with a bat house manufacturer, BatBnB on just that topic. He talks about using it in his home garden and common sense tips for minimizing breathing in the guano dust, which can cause a toxic condition. But following some basic sensible measures he says is minimal if you do it outdoors and practice sensible measures. While I was there, I took a look at Bat BnB’s premade bat houses, and I think I’ll go with one of those if Michael and I don’t manage to make one of our own! They’ve also got a very good Hanging Guide and FAQ section. Scroll down for the video with Dr Tuttle!
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Merlin Tuttle’s Approved Bat Houses
- Austin Batworks
- Bat Bungalows
- Bat Conservation & Management
- Fly By Night, Inc.
- Habitat for Bats
“Selecting a Quality Bat House” from Merlin Tuttle