Thursday, April 18, 2024

A Culex pipien mosquito, a species that feeds on birds and mammals. They can transmit West Nile virus. (Photo: AfroBrazilian via Wikimedia Commons)

Fifty-one species of mosquitoes live in Massachusetts (and 200 in North America!). That’s a lot of mosquitoes; however, only a dozen species transmit diseases that sicken people.

You will find most mosquitoes hanging out in damp, shady areas with lots of plants – they need water in which to lay eggs and plants to hide from predators.

Mosquitoes’ main source of food is plant nectar and fruit juice, but female mosquitoes also need blood to produce eggs. Therefore, only the females bite. To find a blood-carrying victim, they follow streams of carbon dioxide that animals, including human animals, breathe out, and can find a stream of carbon dioxide from 50 feet away. Mosquitoes also home in on the lactic acid produced when you sweat.

Different species require different types of blood. Some feed on birds, turtles and frogs. Others prefer mammals such as horses and people. Some bite birds and mammals, and it is these that can spread diseases between birds and horses or people. In Massachusetts, those are West Nile virus or eastern equine encephalitis. EEE is not a problem in Cambridge because horses are not prevalent, but West Nile virus is found here – currently the risk level is moderate. Examine this risk map to assess virus levels in various parts of the state and what you can do to protect yourself.

An adult female Anopheles quadrimaculatus mosquito captured in Florida in August. This mosquito has parasites – larval water mites – on it. (Photo: Kaylyn Cullen at Beach Mosquito Control District)

West Nile first struck people in 1999 in New York. The following year, it infected people in 12 states. Today it is found in many bird and mosquito species throughout North America, and from 1999 to 2010 infected more than 2.5 million people. Luckily, 80 percent of infected people develop no symptoms. The other 20 percent can develop flulike symptoms: fever, headache, body aches, joint pain and more. In extremely rare cases, the virus can lead to encephalitis or death.

Though mosquitoes seem ubiquitous in some places, most females live for only two weeks, and most males for only one. A female lays eggs on the surface of a pool of water. Each hatches into a larva, sometimes called a wiggler, within two days. Over the course of five days, each growing larva molts several times; feeds on microorganisms, plant debris and other organic particles in the water; and finally develops into a pupa. The pupa does not eat and develops in the water for a couple of days until it emerges as an adult mosquito.

A microphotograph of a Culex mosquito larva taken from a pond. (Photo: Dawolf000 via Wikimedia Commons)

The first Europeans in North America encountered many diseases, including malaria, but did not know what caused the sickness. An Italian physician decided it must be due to “bad air” in marshy areas, so he called it mal’aria. According to Historia Obscura, during the late 1700s and 1800s, fewer than 20 percent of European settlers in coastal South Carolina lived to be 20 years old. Most children died of malaria. Some of this was due to poor drainage around towns and some to the cultivation of rice in wet lands: These settlers were unknowingly raising malaria-carrying mosquitoes as well as rice.

Malaria may even have helped the United States gain independence from Great Britain. According to Smithsonian Magazine, in 1781, Gen. Charles Cornwallis wanted to move his army north to Virginia to avoid “the fatal sickness which so nearly ruined the army” the previous summer. His superiors said no, and Cornwallis instead went to Yorktown. There malaria took hold. By late summer, more than half of his men were too sick to stand duty. In October, healthy American Continental troops, freshly arrived from New England, and French troops defeated the sickly British troops at the Battle of Yorktown, the last battle of the American Revolution.

An Anopheles quadrimaculatus mosquito near Baltimore in August. These mosquitoes can transmit malaria in regions where malaria is prevalent. (Photo: Whitni Brown)

Malaria spread by mosquitoes was common before the 20th century. Perhaps many people remember the scene fromLittle House on the Prairie” in which everyone in the Ingalls family comes down with it? “All of the settlers, up and down the creek, had fever ’n’ ague. There were not enough well people to take care of the sick.” The family is rescued from delirium only when Dr. George Tann, a Black physician drawn to Kansas by the 1862 Homestead Act, stumbles upon them and treats them.

What can we do about mosquitoes today? Spraying for them kills other insects as well, including beneficial bees and butterflies, caterpillars and crickets, beetles and dragonflies and spiders. Ninety-six percent of land birds depend on insects for survival (mostly caterpillars and spiders) through the feeding of their chicks, so spraying also harms them and then other animals higher on the food chain that prey on birds. Insect and bird populations in North America are plummeting, and pesticides play a large role. Mosquitoes are also an important food source for many other critters – from dragonflies to bats to turtles to frogs.

A female Culex mosquito found on a small pond. Most mosquitoes are active from dusk until dawn. (Photo: Alex Wild/Insects Unlocked, via Wikimedia Commons)

Some of the best ways to prevent mosquitoes from living in your yard are to remove standing water or, if you don’t want to remove the water (such as in a bird bath), dumping it every couple of days and starting fresh. If you can’t drain the water, try using mosquito dunks, which release bacterium that target mosquito larvae and biting flies but are harmless to other wildlife.

An organic farm in Cape May, New Jersey, a stopover for migrating birds, had a large mosquito outbreak one year and used an ingenious method to rid itself of these pests while protecting crops and birds from insecticides: County officials used dry ice – frozen carbon dioxide that sublimates into carbon dioxide gas – to attract the mosquitoes to a tiny area where they used a small amount of insecticide spray. The farm has since reduced mosquito reproduction without the use of insecticides.

If you want to enjoy the outdoors at night, wear light-colored clothing – mosquitoes are more attracted to dark clothing than light – and use a couple of fans to keep pests at bay. That’s right. Fans. Studies have shown that wind can disperse the carbon dioxide we breathe out, while the breeze from a fan cools you off; you sweat less, emitting less lactic acid. Contrary to popular belief, the wind does not make it difficult for mosquitoes to fly, just harder for them to find your carbon dioxide stream.

As high school teacher Bert McCoy said, “If you stay long enough in paradise, you’re bound to get bitten by mosquitoes.” There are steps we can take to protect ourselves, though, without harming paradise at the same time.


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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.