Myth: More Wetlands Equals More Mosquitoes

In the mood to blame wetlands for the blood-sucking, possible disease-spreading skeeters in your yard? It’s an urban legend that wetlands are a primary source of the mosquitoes that spread diseases like West Nile Virus.

In fact, a healthy, functioning wetland can actually help reduce mosquito populations. A vibrant wetland ecosystem is home to fish, insects, amphibians, birds, and bats that devour the tiny pests.

And when it comes to combating the spread of West Nile Virus, it’s interesting to learn that this disease is transmitted primarily by a mosquito variety called the “house mosquito.” This species does not prefer to breed in wetlands; instead, it breeds rapidly in stagnant water often found around the home—places like discarded tires, untended bird baths, and clogged roof gutters.

So, healthy wetlands provide wildlife habitat, naturally cleanse our water—and even help control those annoying mosquitoes.

The Situation: Misconceptions About Wetlands and Mosquitoes

It’s true that mosquitoes need standing water to breed, and because of this on a global scale wherever there are wetlands there are mosquitoes. However, scientists recognize that draining wetlands increases rather than reduces the problem.

If a natural wetland is drained, it may still be able to trap enough water after a heavy rain to breed mosquitoes. Although adult mosquitoes have a very short life cycle (from four days to a month), the eggs they lay can remain dormant for more than a year, hatching when flooded with water. Because of this, a drained or degraded wetland area may actually produce more mosquitoes than it did when it was a healthy, functioning wetland!

When wetlands are healthy the mosquito’s natural predators – birds, bats, dragonfly, and frogs (i.e., those species normally found in a “wet wetland”) – can control the mosquito population. Wetland scientists are now investigating the role of restoration (see below) and other land management techniques in controlling for mosquitoes.

West Nile Virus is a mosquito-borne disease transmitted mainly to birds, but also to animals and sometimes people. It has had devastating effect on bird populations, especially among raptors like owls, hawks, crows, and jays; and occasionally has caused illness and death among humans.

The Problem: Wetlands Are Wrongly Accused of Being the Villain

As we mentioned, 70 percent of West Nile Virus cases in humans are associated with a mosquito known as the “house mosquito” (Culex pipiens). This mosquito species doesn’t usually breed in wetlands, and the adults can only fly less than a mile from where they hatched.

Therefore, if your home is more than a half-mile away from a wetland, it just stands to reason that wetlands shouldn’t be your target when it comes to reducing the risk of getting infected with the West Nile Virus. Instead, take a look around your property for some of the house mosquito’s favorite breeding spots—places like old tires, clogged rain gutters, buckets and pails behind the garage, and untended bird baths and baby pools.

Here’s an interesting fact: did you know a single discarded tire can produce over 500 mosquitoes?

The Solution: Reduce Mosquitoes by Restoring a Wetland

Wetland restoration and protection can help decrease mosquito populations in several ways: by providing better quality habitat for the natural predators of mosquitoes, and by helping to reduce flooding and standing water in non-wetland areas that are wet long enough to support mosquitoes—but aren’t wet long enough to establish wetland vegetation and a healthy population of mosquito predators.

Besides, wetland restoration can be smart economics. New Jersey has been controlling mosquitoes “the natural way” by using a technique called Open Marsh Water Management (OMWM). This technique controls mosquito larvae by eliminating low (non-wetland) areas where water temporarily collects and mosquitoes breed, and by enhancing wetland habitat to increase natural enemies of mosquitoes. Insecticides are not used.

One community reported spending approximately $16,000 to implement the OMWM method on a 548-acre marsh in 1969. This expense saved the community hundreds of thousands of dollars of maintenance, cleaning, and pesticide use, which would have otherwise been required to control mosquitoes. Twenty-five years later, the local commission estimated that the cost of traditional insecticide control over this period would have been $685,000. Natural wetlands resulted in a savings of over 97 percent!

And, when the Essex County, Massachusetts Mosquito Control Project restored a 1,500-acre wetland, the mosquito population dropped by 90 percent. The experts there know that wetland restoration is synonymous with genuine mosquito control.

What You Can Do To Help Control Mosquitoes

Mosquitoes need just over a week to hatch and develop into adults that can transmit disease. Here are a few environmentally friendly easy fixes you can do around the house to reduce those pesky pests:

  • Get rid of unused tires, drums, and any other unneeded, water-trapping containers that are stored outdoors.
  • Throw out those old unused buckets, pails, and pots behind the garage (or at least turn them upside down!).
  • Remove leaves and sticks that might trap water in your roof gutters.
  • Cover trash containers (and consider drilling a hole in the bottom so that any collected water can drain away).
  • Store boats and kayaks upside down.
  • Change the water in plastic wading pools and bird baths weekly.

Written by John Sentell, The Wetlands Initiative; James Montgomery, Environmental Science Program, DePaul University; and Bob Kirschner, Chicago Botanic Garden