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Government Takes a Bite Out of the Mosquito Population: Mosquito Abatement Districts, Explained

How local government tries to control the world’s deadliest wild animal—the mosquito.

PUBLISHED NOV 10, 2021 11:54 A.M.
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Mosquitos kill about 725,000 people every year, worldwide.

Mosquitos kill about 725,000 people every year, worldwide.   James Gathany / Wikimedia Commons   Public Domain

When the earliest European explorers landed in San Francisco Bay, they were surprised to find few indigenous people in sight, as they had expected. Instead, they were greeted by massive clouds of whirring, aggressive insects. Two centuries earlier, their Spanish precursors in other regions of the Americas had also encountered these tiny but fearsome creatures, and given them the name “mosquito,” which translates from Spanish as “little fly.”

But the name hardly did justice to the insects, which attacked humans with abandon and caused rashes of itchy bumps, and more seriously—though this was not known at the time—crippling, even fatal diseases such as yellow fever and malaria.

Mosquitos Attack European Settlers in the New World

On the East Coast more than 160 years earlier, the first English settlers in Jamestown, Virginia, learned about the mosquito threat the hard way. Not only did the insects torment the colonists with relentless biting, they inflicted a wave of death on the inhabitants of the Jamestown fort,  rather unwisely built adjacent to a festering swamp.

According to historian Gordon Patterson in his 2009 book The Mosquito Crusades, 51 Jamestown settlers perished within six months of their initial landing due to “fevers,” and over the next decade about two out of every three of Jamestown’s inhabitants died of devastating fever.

Up the coast in what became known as New England, the Puritan settlers, aka Pilgrims, didn’t have it much better. Mosquito bites were one of their incessant complaints. Nonetheless, in Massachusetts the Puritans attempted to prohibit the Native Americans there from smearing their bodies with bear fat to repel the insects—a practice considered “heathen” by the religiously fanatical settlers. One Puritan crusader, John Eliot, assured the indigenous people that “prayer and pains through faith in Christ Jesus” would protect them from mosquito bites.

During the Gold Rush of the mid 1800s, a century after Spanish explorers arrived in San Francisco Bay, mosquitos and their accompanying plague of malaria continued to tear through California.

California Is Home to 53 Mosquito Species

The tiny mosquito has been around far longer than human beings. The first mosquitoes are believed to have evolved as long as 200 million years ago, making them contemporaries of the dinosaurs. The oldest fossilized mosquitoes, discovered in Montana, are estimated to be 46 million years old. Today, all those millions of years later, mosquitoes rank as the deadliest wild animal on the planet, killing about 725,000 humans per year, almost 15 times as many as the second-place snakes, who claim about 50,000 lives each year.

Approximately 3,000 species of mosquitoes exist worldwide, of which California is home to 53, though not all species exist in every county. Santa Clara County, according to the county’s Vector Control District, has about 20 species of mosquitoes. Placer County residents have to cope with more than 30 species—five of which are considered “primary vectors” of diseases that include West Nile virus, Western equine encephalitis virus, St. Louis encephalitis virus and of course malaria. Santa Cruz County lists nine “important” species in the county. And the scope of a district often extends beyond mosquitos. The Sacramento-Yolo Mosquito and Vector Control District, for example, changed its name in 1990 to reflect expanded services to address ticks, yellow jackets and other vectors.

The latest addition to California’s mosquito cornucopia is the Aedes albopictus mosquito, also known as the tiger mosquito. The Aedes, according to a Los Angeles Times report, came to California in 2001 via shipments of “lucky bamboo” from China. They are described as “ankle biters,” because they fly low to the ground.

The State’s Century-Long War Against Mosquitoes

Though there often seems little that can be done to defend against mosquitoes, California has been waging an organized war against the insects for most of its existence as a U.S. state. The Mosquito Vector Control Association of California (MVCAC), the main advocacy group for the fight against mosquitoes, boasts 60 member agencies throughout the state, including 49 special districts dedicated to mosquito abatement. 

Special districts are government entities that exist to provide specific services within a designated area—services that top-heavy municipal bureaucracies may not be able to adequately provide. The first special district in California was formed in the San Joaquin Valley in 1887, to provide irrigation water for farmers there.

In the early 20th century, special districts expanded beyond water delivery to serve a wide variety of needs. One of the most pressing needs was mosquito control. In 1915, just 28 years after the birth of the special district system in the state, the state legislature passed AB 1590, a bill authorizing the creation of special mosquito abatement districts. The bill was signed into law by Gov. Hiram Johnson, a leader of the “progressive” movement who also created the state’s direct-democracy system of ballot referenda, initiatives, and recall elections.

Prior to the law, mosquito control efforts were funded largely by private donations. The fight against mosquitoes may have had as much to do with real estate values as with public health. The 1915 bill was initiated by Hillsborough developer Harry Scott, in collaboration with a medical entomologist, William B. Herms. Johnson signed the bill in May of that year—by November the Marin Mosquito Abatement District became the first to be formed under that law. A month later, a three-city district formed with San Mateo, Burlingame and Hillsborough as members.

Mosquito Abatement Districts Save Lives

A mosquito abatement district's primary service is monitoring water where it appears, primarily in small pools. Water is essential for mosquitoes, who fly through the air to annoy and endanger humans, but actually spend three of the four phases of their life-cycle in water. Female mosquitoes—the only ones who attack humans; male mosquitoes feed on plants—lay their eggs on the surface of standing water pools.

An egg can hatch in as little as 48 hours. At that point, the larvae remain in the water to shed their skin, or “molt,” four times, growing larger with each molt until the larva transforms into a pupa, the final stage before becoming an adult mosquito. Adult mosquitos must rest on the surface of the water before going airborne and seeking their human prey.

Eliminate the pools of water and mosquitoes cannot reproduce. That’s why one of the most important functions of a mosquito abatement district is to monitor private swimming pools—of which there are more than 1.1 million in California. Each of those residential swimming pools is capable, if left unchecked, of breeding one million mosquitoes every month.

Residents of a mosquito abatement district will be asked to keep their pools in one of two conditions, “Clean and Functional” or “Empty and Dry.” District officials may send notices to pool owners asking them to confirm, nowadays usually with an emailed photograph, that their pools meet one of these conditions. A clean and functional pool will have a working filtration system, regular chemical treatments and a water surface that is clear and free of debris or algae. 

During rainy seasons, empty pools frequently collect small puddles of water, and that’s all a mosquito needs to lay a raft of eggs.

An owner whose pool fails to live up to either standard may request, or be required, to have a mosquito abatement service to get rid of eggs and larvae. One technique for accomplishing that task is the release of mosquito fish into the water.

The small Gambusia affinis species thrives in small pools, backyard ponds and other smaller bodies of water populated by developing mosquitoes. The fish control the mosquito population by eating the larval-stage mosquitoes, and were introduced for that purpose to California in 1922. Each fish weighs no more than a few ounces, and only one fish per 20 square feet of surface water is generally required. Solano County Mosquito Abatement District technicians distributed more than 50 pounds of mosquito fish in 2020 alone. That total, during the height of the COVID pandemic, was down from 182 pounds in 2017.

District scientists will also work with affiliated academic institutions to carry out research on and surveillance of mosquito populations with the goal of preventing outbreaks of mosquito-borne diseases.

To find out if you live within the boundaries of a mosquito abatement district, refer to the map at this link, provided by the MVCAC.

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