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Mosquito Season is Back With a Sting

This column originally ran in the May 5, 2008, issue of the St. Louis Post-Dispatch.

If you’ve been outdoors at dusk lately, you know that the mosquito crop this year is likely to be a big one.  The area’s recent rainfall and flooding have produced plenty of standing water for the swarming insects to lay their eggs and reproduce.

That’s bad news for all of us, but there are things you can do to protect yourself and your family from those itchy mosquito bites and the diseases they may carry.

About 165 of the 3,000 different species of mosquitoes can be found in the United States. Because of the shape of their mouths, mosquitoes are on a liquids-only diet, feeding on fruit nectars and blood from humans and animals.

The mouth of the mosquito is actually like a long, thin straw. Female mosquitoes have a mouth that is adapted for piercing skin, and only the females feed on blood. Female mosquitoes obtain their blood meals from warm-blooded animals like birds, deer, cattle, and dogs.

Mosquitoes find their blood meal hosts by smell and vision. Even when the mosquito is far away, she can smell the carbon dioxide exhaled by humans or animals. When she senses it in the air, she follows it to the source by flying in the direction where the carbon dioxide smell is strongest. When she gets closer she is attracted by the body’s heat and moisture. Finally, when she is very close, she uses vision to find a place to land. Mosquitoes are so light and delicate that most people don’t feel them land.

While the mosquito is biting, a pump in the head of the mosquito pumps saliva into the skin. It is the saliva that makes mosquito bites itch, as cells of the immune system rush to the site of the bite to get rid of the saliva. Chemicals released by these cells cause the swelling and itching we all associate with mosquito bites.

This may surprise you, but mosquitoes aren’t all bad.  In fact, adult mosquitoes are important to the ecosystem as pollinators of flowers. Since mosquitoes feed frequently on flower nectar, they carry pollen from flower to flower and can pollinate flowers just as honeybees do.

But mosquitoes are also transmitters of disease. Mosquitoes can pick up viruses or parasites when feeding on an animal infected with the disease. When the female mosquito bites another host and injects saliva, she can inject the virus or parasite along with the saliva. In this way, mosquitoes are very efficient transmitters of several diseases.

Some mosquito-borne diseases occur in the United States. Among the mosquito-transmitted diseases occurring in the United States are four viruses, known as encephalitis viruses because they attack the brain of the human host. Mosquito-transmitted encephalitis viruses in the United States include western equine encephalitis, eastern equine encephalitis, LaCrosse encephalitis, and St. Louis encephalitis (so named because the virus was first identified in St. Louis in 1933).

Three of these viruses - eastern and western equine encephalitis virus and St. Louis virus – use birds as reservoirs. Normally, the virus infects a bird; a mosquito feeds on the bird; then the mosquito feeds on another bird to keep the cycle going. Humans become infected when one of the infected mosquitoes bites them. However, humans can’t infect other mosquitoes. Eastern and western equine encephalitis viruses have the word equine in the name because they make horses sick, as well as humans.

Another mosquito-borne illness involving birds and humans is West Nile virus. The arrival of West Nile virus in Midwestern states has made mosquito protection a greater priority.  At greatest risk of serious illness are people over age 55, but protecting children from West Nile and other diseases remains important.

Products containing DEET (diethyltoluamide) are the most effective insect repellants.  The American Academy of Pediatrics recommends use of DEET in concentrations of no more than 30 percent when used according to product directions.  DEET in a 10-percent concentration is protective for about two hours, and 24-per cent DEET is effective for an average of five hours.

To protect yourself and your family:

  • Avoid areas where insects nest or congregate. During outdoor activities, do not wear bright colors; flowery prints; or scented soaps, perfumes or hair sprays.
  • DEET is effective against mosquitoes, biting flies, fleas, gnats, chiggers and ticks, but not against stinging insects.
  • Side effects are associated with the overuse or oral ingestion of DEET, or the use of DEET in concentrations higher than 30 percent.
  • Do not use products that combine sunblock and DEET – sunblock should be applied repeatedly, but DEET should be applied once a day. Insect repellants should be applied sparingly to exposed skin or clothing, but not under clothing.  DEET is not recommended for children younger than two months old. 
  • Do not use DEET on the hands of younger children; around the eyes or mouth; or over cuts, wounds or irritated skin.  Wash treated skin with soap and water after the child returns indoors. Also, wash treated clothing. Avoid spraying insect repellants in enclosed areas. Do not use near food.
  • Permethrin (Permenone spray) is an alternative insect repellant suitable for children with sensitive skin. Permethrin is applied to clothing, where it dries and bonds to the cloth for up to six weeks, even after laundering.


Dr. Bob Wilmott is Chief of Pediatrics at SSM Cardinal Glennon Children’s Medical Center and is a Professor of Pediatric Medicine at Saint Louis University School of Medicine.

(From the Centers for Disease Control and Prevention)

  1. An adult mosquito can live as long as 5 months. It may take several months for a larva to develop to the adult stage in cold water. Eggs of floodwater mosquitoes may remain dormant for several years, and hatch when they are covered with water.
  2. An adult female mosquito weighs only about 1/15,000 ounce (about 2.0 milligrams).
  3. An adult female mosquito consumes about 5-millionths of a liter in a single blood meal.
  4. A mosquito wing beats from 300 to 600 times per second. Male mosquitoes find female mosquitoes by listening to the sound of their wings beating.
  5. The males can actually identify the correct species by the pitch of the female’s wings.
  6. Mosquitoes can fly about 1 to 1.5 miles per hour.
  7. Most mosquitoes do not fly very far from their larval habitat, but the salt marsh mosquito migrates 75 to 100 miles over the course of its life.
  8. A mosquito can smell the carbon dioxide you exhale from about 60 to 75 feet away.
  9. Some people are more attractive to mosquitoes than others. It is not clear why, but probably has something to do with the 300 odd chemicals produced by the skin.
  10. In the interest of science, Arctic researchers uncovered their chests, arms, and legs and reported as many as 9000 mosquito bites per person, per minute. At this rate, an unprotected human would lose one half of his blood supply in approximately 2 hours.


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