Low-tech and effective, rain barrels collect rainwater from your roof, which reduces storm water runoff and pollution. Harnessing an otherwise unused source of water provides the added benefit of household water conservation. Despite their advantages, rain barrels can lead to problems with mosquitoes, since standing water provides an ideal breeding habitat for the insects. The potential for mosquitoes shouldn't discourage you from enjoying the benefits of rainwater collection. Keeping mosquitoes from breeding in your barrel is as simple as employing several basic preventative maintenance activities.
Sealing Your Barrel
Whether you build your own rain barrel or purchase a ready-made model, make sure it is completely enclosed to prevent mosquitoes from entering. Fine mesh screens sealed with caulking typically cover the inlet opening of purchased rain barrels. If you construct your own, you can duplicate the screen-and-caulk method of store-bought barrels or employ another type of straining cover. A guide published by the city of Bellingham in Washington suggests stretching and tightly securing nylon stockings over openings as an alternative to screens.
Cleaning Your Gutters
While tightly sealed straining covers work well at preventing adult mosquitoes from finding their way into your rainwater, mosquito eggs and larvae are small enough to reach places adults cannot. Even a small amount of debris in your gutters can create enough pooled water for mosquito larvae to thrive, and heavy rain can wash eggs and larvae through the screen into your barrel. Keeping gutters debris-free and flowing properly is an important step in preventing mosquitoes from breeding in rain barrels.
Draining Your Barrel
Mosquitoes lay eggs on the water surface or near areas that flood periodically. Standing water is necessary for mosquito breeding, because the insect spends its entire larva and pupa stages in the water. Emptying your rain barrel interrupts the life cycle, and because some varieties of mosquitoes reach adulthood within seven days of egg laying, draining your barrel each week is a good idea.
Biological Control
Severe mosquito problems in your rain barrel may warrant the use of a bacterial larvicide, such as Bacillus thuringiensis--Bt. Available in granule, powder or liquid form, the Bt bacterium occurs naturally in soil and kills mosquito larvae. For this pesticide, the U.S. Environmental Protection Agency has waived routine infectivity and pathogenicity studies usually required because Bt has no history of toxicity in mammals. While Bt is recognized as safe for plants, humans and animals, use the product only as directed and as a short-term control method when all other methods have failed. Bt is toxic to caterpillars, some beetles and black flies, and prolonged use and/or overuse of the substance could affect the biodiversity of an area once it leaves your rain barrel.
References
- City of Bellingham Public Works Operations: Collecting Rainwater A Guide to Rain Barrels
- University of Kentucky: Mosquitoes Practical Advice for Homeowners
- U.S. Environmental Protection Agency: Re-registration Eligibility Decision - Bacillus thuringiensis
- U.S. Environmental Protection Agency: EPA's Regulation of Bacillus thuringiensis (Bt) Crops
- Wiley Online Library: Freshwater Biology: Disturbance to a Stream Food Web by a Bacterial Larvicide
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