How to Use Bats for Natural, Non-toxic Mosquito Control
With new mosquito-borne diseases in the US, these wild and mysterious allies provide safer solutions than poisonous sprays.Posted Jul 29, 2014
In North America, we tolerate mosquitoes as a frustrating but wholesome element of outdoor summer activity. Swatting a few in the garden or around the campfire, we barely notice the little bloodsuckers, though we may curse their itchy bites later. Unfortunately, unsettling trends suggest we might join more tropical climates in fearing mosquitoes, who could bring new diseases to our temperate zones.
This summer, one confirmed case of the potentially-deadly Eastern Equine Encephalitis (EEE) was confirmed in Massachusetts: this virus can cause brain damage or death after a single infected mosquito bite. Climate change may encourage the migration of South and Central American mosquito strains — these new arrivals have the potential to spread malaria and other viruses at our formerly carefree backyard barbecues and lakeside holidays.
We’ve already seen mosquitoes (who cause 3% of deaths) responsible for domestic West Nile Virus outbreaks, and the problem is likely to increase alongside new weather disturbances. But before you pull the blinds and stay on the sofa for the season, take heart. Luckily, there are natural bug repellants that work, and avoiding certain mosquito-plagued hours (early morning and evening for a few hours around dusk) drastically reduces exposure.
Choosing a more proactive approach, some winged furry creatures are eager to help us with our infestation, if we help them in return with a little hospitality. Before we poison our gardens and natural areas with insecticide sprays (which may cause more health problems than they prevent), let’s look into collaborating with our ecosystem to create a safe outdoor zone where our family can relax.
Bats control insect populations all the time, whether we know it or not. A single bat can consume up to 1000 mosquitoes an hour! Sadly, common illusions about these helpful animals have cast bats as dreadful vampiric figures of horror movies, and many of us shudder at the sight of a bat. In fact, North American bats are mainly peaceful insectivores. Contrary to myth, they do not have higher rates of rabies infection than most other mammals, and tend not to exhibit stereotypical aggressive behavior when rabid (dead bats should be treated like any other dead wild animal: use no-touch methods to remove it from human areas, and call Animal Control).
It is the bats themselves who are in great danger. In addition to habitat destruction, within the past eight years, up to 7 million North American bats have died from White-nose Syndrome, a poorly-understood fungal infection, which has the potential to cause total extinction of some bat species if trends don’t improve.
Humans and bats need each other: let’s take steps to form a healthy working relationship.
Build them a house
Your attic is no place for bats, as anyone who has cohabited with a bat colony can attest! Their smells and sounds can filter through the walls, and evicting them may require a professional. One of the many benefits to offering a custom-built home for your local bats: it will decrease their incentive to roost inside your home (bat-proofing your living spaces is a good companion project), or under the eaves where their poop may impact human traffic. If you’re handy with basic tools, making a bat house is a simple and fun project, and a great science project for kids. A little planning pays off: choosing the proper location, design, and materials greatly increases the chances of successful habitation.
- Bat families need cozy, warm dens to raise young. Internal summer temperatures of 80-100F are ideal. Some species, including the common little brown bat, will tolerate heat in excess of 100F. We might call it “stuffy”, but bats feel right at home! Lone male bats aren’t as particular and will sometimes occupy nooks with less-ideal nesting temperatures.
- Dark colored materials or paint attract heat, and caulking helps retain it. Common sense tip: use dark paint in cool climates and light paint in hot areas! Use a thermometer taped to a pole to check the temperature in various chambers on hot and cool days to get an idea of the average.
- Leave the inner surfaces unpainted and unsanded, as the bats will only roost on rough natural materials. For roosting purposes, use a router to groove the inside every half inch on the front and back surfaces, or install polyethylene plastic mesh.
- Bat houses attached to a building or pole are easier for bats to find, and therefore more successful, than those attached to trees. In northern climates, bat houses attached to a human house are recommended as they stay much warmer, while in southern climates pole houses work fine.
- The southern, south-eastern, or south-western faces of a building are generally best, assuming those sides have good sun exposure.
- Bat houses generally have open bottoms to avoid guano build-up; take care not to locate bat houses directly over a deck or walkway or other heavily-used area, or over any door or window. Bat guano is sought-after as fertilizer: use a shallow tray to collect it for your garden (avoid deep buckets as baby bats may fall from the nest and get trapped).
- If you’re concerned about guano or bat urine residue on your walls, use 2-4 inch spacers between the bat house and wall, or a large backboard. Though some have tried attracting new bats by using guano as a lure, evidence suggests this does not work.
- Bats like houses at least 15 feet high and with plenty of open space around and below for swooping out into the night. Try to allow a radius of 20 feet around the house.
- Think about bat habitat when starting new construction or renovations: even a gap under a cedar shingle can be a home, or a nook created by a well-placed siding board.
- Take advantage of a variety of free bat house plans available online. Keep in mind that a bat’s ideal nursery is the crevice between the bark and trunk of a tree — they love tight, rough spaces! So don’t be tempted to make it roomier or smoother in hopes of “improving” your bat house.
Include bats in your garden plan
In addition to gobbling up some common garden pests, bats provide another important service as pollinators. If you enjoy gardening or landscaping, you can create a sanctuary where these intriguing creatures will flourish. Keep in mind that even if bats are roosting on or near your home, at dusk they may simply swoop off to their preferred feeding sites if your surroundings don’t feel right. Ask them to stay by planting their favorite treats.
- Bats, like all creatures, need water to survive. A garden pond provides the foundation for a local ecosystem; in smaller spaces, a birdbath will do the trick. Change the water twice a week to avoid hatching additional mosquitoes!
- Night-scented flowers such as honeysuckle, evening primrose, or border phlox are delightful to bats — remember, as nocturnal creatures, the world of color is lost on them. Human inhabitants alike will revel in these evening sensory delights: the scent of jasmine floating through your window as you drift off to sleep is like free aroma-therapy.
- Bats appreciate rows and lines, such as hedges or columns of trees. These linear pathways provide safe flight-routes where bats feel protected from birds of prey.
- Your garden becomes most attractive to wildlife when you allow parts of it to undomesticate. Bats and other creatures are drawn to forest and meadow-like areas which they recognize instinctively as home.
- Mature trees will increase the appeal of your yard or garden. Bats like to hunt in the canopy rather than close to the ground, and feel more protected than when open to the sky.
Young and old alike get a thrill sitting on the porch at dusk and watching shadowy shapes flit and swoop at dizzying speeds — bats go about their business without approaching our realm, as their sophisticated sonar allows them to avoid large mammals with ease. It’s high time we made friends with these misunderstood creatures. Though often characterized as “mice with wings,” evidence suggests bats are more closely connected with humans than with rodents. Studies have suggested some bats are descended from early primates. They groom themselves as obsessively as house cats, love to live in community, and are even known to exhibit helping behaviors, offering food to a needy neighbor.
Of course there are other approaches to non-toxic mosquito protection: pheromone-based mosquito traps are quiet and effective, electronic “bug zappers” increase the peace for dinners on the deck, and the screened porch never goes out of style. As our climate changes, bats as well as humans will face greater challenges. Before mosquito-borne diseases increase dramatically in our towns and wilderness areas, let’s take steps to give our bat allies their own safe haven to continue their crucial work.