Mosquito larvae form dense groups in standing water. Credit: James Gathany via Wikimedia Commons

By Lucca Ammann


It’s my first day of work, summer 2022. I’ve been hired as a lab intern for North Shore Mosquito Abatement District (NSMAD), a building 5 minutes from my house, unknown to me until my first day of work.  

A blast of AC welcomes me into the building, followed by awkward confusion about where to go and what to do. After I waver a moment in the doorway, a few middle-aged male managers approach and take me on a quick tour of the building — the lab, break room, and enormous garage with every inch filled by rows of shiny red pickup trucks. In the corner closest to the lab I see industrial looking freezers and tables piled with equipment — nets, containers, microscopes, and tons of other equipment are stored on shelves. I am led from the hot, dark, concrete garage into the cool, white, and shiny lab.  

NSMAD Vector Biologist Christopher Xamplas extracts DNA from a mosquito sample. Credit: Lucca Ammann

Two cold tables, originally meant to be used in an ice cream store but cleverly recrafted, are on an island in the lab. A large freezer and PCR test equipment are nestled along the countertops. “PCR” might sound familiar — it’s the same process used to test for Covid, and it stands for polymerase chain reaction. The test basically seeks out and amplifies the virus DNA we are searching for. One of my new coworkers is sitting at the island counting mosquitoes. Weird that I would soon know what the black pile of bugs is and what she’s doing with it, and that the stranger sitting at the island would quickly become a good friend.  

Back in the garage I am handed an assortment of gear, including, but not limited to, navy “NSMAD” T-shirts, which I’ll be wearing every day, and an “NSMAD” bucket hat (later stolen by my mom), along with a yellow reflective work vest. Hot. The only truck left for me to claim for the summer is the oldest and largest in the garage, a Ford F-250 (and I have never driven a truck). Awesome.  

Before I landed this summer job in a mosquito lab, outside of looking at bugs in the park as a kid, I had no interest in the subject. I had never studied entomology or cared about insects. But as a 21-year-old I was thrown into the wacky world of mosquito abatement and was forever changed by it. At that moment the lab seemed sterile and cold, but I would soon learn it is filled with warmth, curiosity, and often chaos.  

Everyone hates mosquitoes. Their buzzing around you all summer long is infuriating, and their bites are itchy and painful, sometimes leading to sleepless summer nights. But they are also a serious source of disease. Mosquitoes are the deadliest animals on Earth. Around 725,000 people are killed and millions infected by mosquitoes every year. Mosquito-borne diseases, such as malaria and Zika, have been ravaging the global south for centuries now.  

For most of the past century, the U.S. hasn’t had to worry about mosquito-borne diseases. We don’t have to fear that our common mosquito bites will lead to getting sick from the innumerable vector-borne diseases in the world, thanks to mosquito abatement. Other parts of the world do not enjoy this luxury. Countries close to the equator are typically bombarded by mosquitoes and their diseases. Mosquito abatement programs have been a success in our country, but with global warming opening up more regions to mosquitoes, the battle is getting harder and harder to win, even here in the Midwest. African and Asian countries have malaria; the Chicago area faces the threat of West Nile Virus.  

During my summer on the front lines, my contribution to mosquito abatement consisted of surveying a given area, reducing breeding sites, dropping larvicides, and testing adult mosquitoes for West Nile Virus. Every morning at 7:30 a.m., a stream of red pickup trucks filed out of the NSMAD parking lot.  

A gravid trap, used to catch mosquitoes. Credit: Lucca Ammann

We collected gravid traps — a tub of stink water with a battery-powered fan pushing air from above the tub into a net. Female mosquitoes (at least the ones we were after) lay their eggs on water, so as they were attracted to the water to lay their eggs, they get blown into the net. “Stink water” is aptly named, as I smelled it before being properly introduced. It is rabbit food and water placed in the sun to ferment in a huge tank and then divided up into containers to carry to the traps. One summer morning, I spilled a whole bucket all over the bed of my truck and the garage driveway. (I was not popular that day.) I was convinced of the apt name every day thereafter as our trucks perpetually wafted the foul aroma along the Chicago North Shore.  

Later, after collecting the traps, we returned to the lab to organize and prepare nets for PCR testing. “Doing the nets” felt very labor-intensive at first; we hand-counted, gendered, and speciated each mosquito from every net. Picture me, hunched over the cold tables going “122, 123, 124…” as I moved around individual mosquitoes with tweezers. I later learned that we not only want to collect the mosquito that carries West Nile Virus, but also to use the nets as general surveillance to see all species currently present in the area. There are 28 traps spaced out across the NSMAD district.  

This process was organized by Christopher Xamplas, Vector Biologist at NSMAD for 13 years and my supervisor. He had the job of wrangling our team of four lab staff. Xamplas and my coworkers taught me everything I needed to know, from trap collection to PCR testing, and now, the history and future of mosquitoes and abatement.   

North American abatement first started in the early 1900s, when malaria was a huge issue. Xamplas explains that without mosquito abatement, “if you were to travel through Chicago in the late 1800s-early 1900s you were probably going to catch malaria.” It was a normal summertime illness, unavoidable, for centuries. Now malaria is eradicated in the U.S. and an issue for most people in the global north only when traveling. For example, I’ve had to take preventative malaria pills during a trip to Thailand. (Warning: They give you very weird dreams.)  

The new threat, West Nile Virus (WNV), originally arrived in 1999 in New York and spread rapidly across the country. It is thought to have been brought over on a cargo ship carrying tires containing infected Culex eggs. Soon after the ship docked, birds at the New York Zoo started dying, and then humans became sick. By 2002, U.S. outbreaks were at an all-time high, including in Chicago.  

“For a number of reasons the entire Chicago area is a hotbed for West Nile Virus,” Xamplas says. Due to the area’s swampy history, mosquito populations thrive. Standing floodwater, outdated sewer and drainage systems, and humid summers create a lovely mosquito oasis. The urban landscape of man-made water catch basins have exacerbated this mosquito environment, especially for the Culex mosquito.  

The Culex genus of mosquito, especially Culex pipiens, spreads WNV. Pipiens is known as the common house mosquito because of its ability to seek out and breed in any urban standing water. Birds are a common vector. “The Culex restuans,” Xamplas explains, “is primarily an avian biter,” and the West Nile Virus prefers to harbor in robins. “So you have the restuans biting and then spreading WNV amongst the bird population. Then you get a mosquito like the pipiens, the house mosquito which lives around people. They will feed on birds while also having a preference to feed on humans. You get the mosquitoes bridging the WNV from the birds onto people.”  

As this description may suggest, most species of mosquitoes are, surprisingly, not primarily human feeders. They started feeding on us as we began forming larger villages and cities. With denser human populations and reliable water reservoirs, we became attractive. Some mosquito species basically “evolved” to rely on our urban water for breeding, and us for food, and hence became “specialized” to humans. Culex pipiens is a prime example.  

In the lab, we collected female pipiens (the males don’t bite) to test for traces of WNV. Every summer, when we first detect WNV the public is alerted and testing ramps up. Friends and family constantly asked how I avoided contracting the disease, but because of abatement, human cases are relatively low. There were only 1,035 reported U.S. cases in 2022, and 30 cases in Illinois. While looking through the years of national and NSMAD data on WNV, I expected to see declining cases. Unfortunately, I was only partially correct. There is a huge correlation between high WNV cases and weather. After a summer storm, we spent more time hunting for breeding sites and occasionally using larvicide.  

During my summer as a mosquito lab technician, we also aided in a research project on the breeding habits of Culex restuans and Culex pipiens. Whenever we had time, we headed off to explore our urban wonderland of abandoned tires and dirty buckets. Nine times out of 10, little larvae would be swimming around and looking back up at us. The number of breeding sites we found was shocking to me. Anything that can catch rainwater and sit for a few days can breed mosquitoes. Females can lay eggs in the water, which then turn to larvae, pupa, and eventually adult mosquitoes, who then fly away from the catch basin and terrorize your neighborhood. These mosquitoes are thriving in our urban world of waste.

Since mosquitoes require warm climates, the U.S. only sees them during the summer. But record-breaking warm summers are changing ecosystems and extending mosquito season. A longer mosquito season means more disease transmission and more time to crawl north. Zika virus is typical in this regard. Though the virus has been around for almost a century, its entry into the U.S. during the summer of 2016 caused a panic, and deaths. It is certain that globalization will continue to spread mosquito species, but so will global warming impacts. 

Hotter, wetter summers result in more mosquitoes, and therefore more WNV, and the weather is increasingly harder to predict. Low numbers one summer do not promise low numbers the next, which makes consistent abatement support and funding an issue. In 2012, after abatement funding in Dallas County, Texas, was reduced, mosquitoes began to appear in relatively larger numbers than normal. WNV was detected in the first mosquito samples of the summer, so the county started routine larvicide applications until August, but it was already too late. Dallas County began to experience one of the worst WNV outbreaks since the disease originated in the U.S. Only after the outbreak was labeled an endemic would more extreme measures, such as truck and aerial pesticides, be used. A total of 1,763 illnesses were confirmed in the country that summer, and 81 people died. Prevention and WNV monitoring now starts in May, or right when mosquitoes begin emerging for the summer.  

Credit: Koko Nakajima via NPR

Brian Allan, a Professor of Entomology at Illinois, studies vector-borne diseases, especially how our environment and these diseases are affected by each other. I asked him if climate change is going to increase the threat of mosquito-borne diseases. His answer is complicated; it’s a multifaceted problem. While “lots of scientists have made reasonable predictions that climate change will alter vector-borne disease risk,” Allan says, “one of the big predictions is geographical shifts. Diseases we’ve always thought of as tropical diseases [are] suddenly occurring in the southern U.S.” What’s harder to tease out, though, is “how much are those changes in distribution being caused by change in climate, versus are they being caused by other things changing, like humans moving around and bringing mosquitoes to new areas.” In other words, global population movements, climate change, and vector-borne diseases are inextricably linked.  

Deforestation is another complicating factor. “Deforestation,” Allan continues, “is probably a more major driver of disease emergence than is climate change right now.” It affects the habitat of animals, which alters the “geographical distributions of vector-borne diseases.” My boss also emphasized the risk of disastrous weather, especially hurricanes. “Imagine there’s a hundred miles knocked out by a hurricane,” Xamplas says. “Swimming pools are left to breed, flooded areas, places holding water are not taken care of.” In places like Florida and Louisiana, mosquitoes can make it unbearable for search and rescue and rebuilding efforts.  

Our mosquito problem can be exacerbated in many ways, but one thing entomologists know is that a new mosquito-borne disease is coming. “There’s inevitably going to be another virus, another West Nile,” Xamplas says, and Allan concurs. Over the past century of abatement there has been a pattern of diseases popping up. By the time one disease is under control in an area, a new one begins to emerge. Before WNV was St. Louis encephalitis, and before that, malaria. We still check for St. Louis encephalitis in our mosquito samples, just in case the next wave of vector-borne disease is one from the past.  

My strange summer job ended up being an incredibly unique experience. The lab and the Ford F-250 became home, and I still think of the giggling of my coworkers as we count thousands of mosquitoes by hand with music playing in the background. I see Xamplas giving disapproving looks (always followed by a chuckle and a wave) as we pile into the truck to search for breeding sites, and probably ice cream. I never felt threatened or scared by mosquitoes or the diseases they can carry. It was all very controlled.  

But behind my fond experience lies a darker reality. While Culex pipiens was by far the most abundant mosquito species collected, we saw many different species in the nets. The new species seemed to grow in abundance as the summer went on. To us, these discoveries were exciting. The whole office would fan-girl and take turns looking at them under a microscope. Alarmingly, in retrospect, we found an increasing number of Aedes japonicus. “I found 10 my first year here,” Xamplas says, “and now we get over a thousand every year. (It) incrementally increased until it became the third highest numbered mosquito in our traps.” Aedes japonicus is known for transmitting yellow fever, dengue fever, Zika, and chikungunya virus. Although Xamplas wavered over attributing their increasing numbers to climate change, he did admit that given “one mild winter they can survive long enough to inch their way north.” Without intensive abatement, I now realize, our summers would be unbearable, and many more lives would be lost. While we may be winning our local battle, the future of the war is uncertain. Globally, the situation is much less controlled, while the threat of a new mosquito virus outbreak hangs over Chicago every summer like a humid cloud. The odds, after all, are in the mosquitoes’ favor.  

Summer rain in Chicagoland is often a precursor to swarms of mosquitoes. Credit: Robert Lawton via Wikimedia Commons