All the Buzz About Mosquitoes

Forest Preserve Weekly West Nile Monitoring Report (link)

Mosquitoes are known for their irritating bites, but they’re also important members of the food chain. Mosquito larvae (aka juveniles) help keep marshes and ponds clean by eating bacteria, algae and microscopic plants and animals. (Just one can filter half an ounce of water a day, so a summer’s worth provides a significant environmental service.) In turn, both larvae and adults are food for dragonflies, frogs, fish, turtles and other animals.

Adult mosquitoes live in the shade of shrubs, grasses and other plants but breed in areas near water, where females lay their eggs. Some lay their eggs on the surface of ponds and marshes or on floating vegetation; others look for areas only periodically wet, such as depressions in the ground, bird baths or buckets.


Image by CDC/James Gathany

When the weather is warm, mosquito eggs can hatch into larvae within a few days. The larvae remain in the water, but because they need air they’re usually near the surface. They swim around by making jerky movements with their bodies, which gives them the name “wigglers.” In about a week they develop further into pupae, which stay in the water for a few days before emerging as adults.

Both male and female adult mosquitoes get their energy from eating nectar and other plant juices. They use a long tubular mouthpart called a “proboscis” to suck up the liquid. With most species, the females also take in blood but not for food. Some cannot produce eggs without the proteins found in blood; others can produce eggs on their own but lay more after a blood meal.

As a result, even though male and female proboscises have the same basic six parts, those on a female are sized and shaped differently. Two of the parts cut through the skin, two likely help keep it open, one pierces the blood vessel and sucks out the blood, and one deposits saliva. The saliva contains a chemical that keeps the blood from clotting (and causes bites to itch), but it may also help the insects locate vessels in the first place. The saliva is also the substance that carries diseases from infected mosquitoes into the animals they bite.


In the Forest Preserves

Mosquitoes are an important part of the food chain, so under normal conditions the Forest Preserve District does not attempt to eliminate them. But with the arrival of West Nile virus, the District’s fundamental concern for the health of county residents and forest preserve visitors spurred the start of a comprehensive mosquito monitoring program that continues today.


How Is the Forest Preserve District Addressing West Nile Virus?

The Forest Preserve District’s mosquito monitoring program focuses on Culex mosquitoes, the species most likely to transmit West Nile virus in northern Illinois. 

Culex are “drought-driven” mosquitoes. Rather than reproducing in healthy wetlands or after heavy rains, they lay their eggs in warm, stagnant surveillance waters formed after long dry spells.

The program follows Illinois Department of Public Health guidelines, which advise public and private landowners alike to focus first on monitoring areas for Culex larvae and using a larvicide where they’re found. The larvicide is made from a natural bacterium that targets and kills Culex larvae before they can become adults; very few other insects are affected.

To prevent breeding grounds from developing, District employees drain water from trash bins, buckets, gutters, truck beds, anywhere it can collect. They treat stormwater catch basins in forest preserve parking lots with larvicide.

Each week employees licensed by the Illinois Department of Agriculture also look for Culex larvae at more than 130 select sites close to neighborhoods, parking lots, visitor centers, picnic grounds and other high-use areas that have natural waters with very few fish or other larvae-eating animals. If they find Culex they treat the water with larvicide. They also test adult Culex for the presence of West Nile virus to identify areas with an increased risk of transmission and a need for closer larval monitoring.

The Forest Preserve District shares its findings on an ongoing basis with regional, state and county health departments and collaborates with agencies outside of the mosquito breeding season. 

Forest Preserve District policy does allow for the use of sprays that kill adult mosquitoes but only as a last resort. The chemicals dissipate after only 48 hours and can kill any insects they contact, including butterflies, moths and lightning bugs. The Forest Preserve District will only consider its use if four specific criteria are met:

  1. The DuPage County Health Department’s personal protection index (link) for West Nile virus is at level three.
  2. Data conclusively shows the source of targeted mosquitoes is on Forest Preserve District property.
  3. The delivery of sprays or fogs are able to effectively target specific areas.
  4. No other reasonable alternatives to protect the public from an imminent threat of serious illness or death (such as closing a forest preserve) are available.


What About Zika?

The Zika virus is spread primarily through the bites of infected Aedesalbopictus and Aedes aegypti mosquitoes, both rare or non-existent in northern Illinois. (To date, people in Illinois infected with Zika acquired the disease outside of the U. S.) Both species prefer to lay eggs in tires and other abandoned or neglected items that hold water, breeding grounds not normally found in natural areas.

Of the two mosquitoes, A. albopictus has a potential to be in Illinois, but scientists believe the few previous reports north of Peoria were rare, isolated incidents and not from established populations. Still, because even a remote potential exists, the Forest Preserve District is using a special trap designed to effectively capture Aedes mosquitoes. It’s the same type of trap being tested by the IDPH, the DuPage County Health Department and other agencies.


How Can I Avoid Bites?

Homeowners are often surprised to learn their own backyards offer ideal breeding grounds for Culex mosquitoes. We can all greatly reduce the risk of getting mosquito bites near our homes by keeping yards clean and dry.
  • Empty standing water from toys, flower pot drip pans, gardening equipment and other containers.
  • Clean clogged gutters.
  • Tightly cover rain barrels with lids or 16 mesh screening.
  • Empty and clean neglected swimming or wading pools and bird baths twice a week; empty pets’ water dishes daily.
  • Repair faulty faucets or leaky pipes.
  • Visit the IDPH website for more tips.
In addition, the Centers for Disease Control and Prevention offers recommendations for avoiding bites no matter where you are.
  • Stay indoors at dawn, dusk and in the early evening.
  • Wear light-colored, long-sleeved shirts and long pants.
  • Use insect repellent containing DEET when spending time outdoors. Be sure to read and follow the product directions, especially when using the products on children.
  • Visit for additional tips.