Stormwater runoff is the largest source of pollution to the Grand River, but it has another consequence you might not have realized: runoff can be a major source of mosquitoes!
These familiar insects are annoying and can even present potential health risks, as certain species are known vectors for disease. Yellow fever, dengue fever, Encephelitis, West Nile Virus, and Malaria are all transmitted by mosquitoes. In some parts of the world, mosquitoes are attributed to millions of deaths per year. Although in temperate countries mosquitoes are more of a nuisance species, Michigan has confirmed cases of West Nile virus every summer. The death of a Macomb county man last month is believed to have been caused by the mosquito-borne West Nile virus.
There are 41 genera of mosquitoes, including some 3,500 species worldwide; despite this wide variety, all mosquito species have something in common: they need standing water to complete their life cycle.
Cases of West Nile virus and other mosquito-transmitted diseases are most common during months of heavy rain, due to accumulation of water that can be used as breeding habitat. After a heavy rain, water may collect in low-lying areas of yards and fields; if this water doesn’t drain within 48 hours, it becomes a mosquito nursery.
You can help prevent population explosions in your own yard if you take a few precautions. If you have soil that drains slowly, you can install rain gardens in low-lying areas to facilitate drainage and prevent standing water after a rain. Rain gardens are beautiful additions to yards that make use of native plants to filter runoff before it drains into the nearest creek or lake; a properly designed rain garden will prevent mosquitoes from breeding in runoff and help keep your watershed clean.
Garden and yard features can also provide breeding habitat for mosquitoes if not properly designed. For example, backyard fish ponds should have varying depths to promote a variety of plant and animal life, including an area deep enough (3-4’) to harbor natural predators of mosquitoes larvae. The water in bird baths should be changed every 2-3 days and rain barrels should be tightly covered.
Keep in mind the features that mosquitoes look for when selecting a breeding site. Females will generally choose a pool of stagnant water less than three feet deep and free of natural predators like birds, fish, spiders, and certain insects. Eliminate all sources of these makeshift habitats from your yard, and the pesky flies will have nowhere to breed. A little attention to detail can help keep mosquito populations down and help prevent the spread of disease. For more information on mosquito control, visit the EPA’s website or the Michigan Association of Mosquito Control.