There is a line across the country above which winter nighttime temperatures average below freezing. That line crosses our area in the general vicinity of Staten Island, or just below it. (Climate warming has it shifting toward the Bronx someday.) Mosquitoes notice that line; if they are above it, some of those camping out till summer do not last. There are caveats to the rule—rains can help or hinder a particular species of mosquito, for instance, and some find shelter in places like sewers, where the ravages of winter are lessened—but we can say that if mosquitoes could read, they would be inclined to like the news about global warming. We can also say that after any extreme weather event, such as last winter’s lack of severe cold or our warm early spring, mosquito-control people get anxious.
Thus, health-department personnel are now tromping out to check discreetly placed mosquito traps. And helicopter pilots are being booked to spray the city’s marshes, and even certain parks, with larvicide, which kills the mosquito before it flies. This year’s war on mosquitoes has officially begun.
4. Maybe “Scourge” Is Too Strong a Word
On the other hand, most mosquito experts know better than to predict. Nobody counts total mosquito populations; there’s sampling and numbers from those tracking West Nile, but mostly, you consider a particular mosquito’s lifestyle (river, beach, sewer, tidal floodwaters, or fresh floodwaters), watch the weather, and guess. “The forecast is difficult to really nail down,” says Roger Nasci, of the arboviral-diseases branch of the Centers for Disease Control. Scott Crans, a mosquito expert at Rutgers University’s Center for Vector Biology, agrees: “It’s not an easy explanation.”
Weather is everything for mosquitoes, but the environmental variables are complex, and different mosquitoes hatch under different conditions. A sewer-based mosquito likes a long hot summer with not too much rain, since rain washes away its eggs. A mosquito that lays its eggs in a floodplain, on the other hand, needs rain—the eggs won’t hatch until water reaches the eggs, parked in the mud of the vernal pond or drainage basin. And this year, there is an argument to be made that, despite the temperature, the weather could be working for us: This winter was relatively dry, thus depleting habitat for those who like to lay eggs in wetland ponds, and the spring came early, meaning many mosquitoes emerged from their eggs early, making them vulnerable to a spring freeze. Depending on the species of mosquito, cold can equal death.
5. The Enemy
Looking closely at the mosquitoes biting you, you’ll see a lot of different kinds out there: about 150 species in North America and close to 60 in the New York area (3,000 in the world). At any given moment, dozens of species dart and hover over the city, wings beating at an estimated 250 to 600 beats per second, like airplanes about to take off from JFK, La Guardia, and Newark. Those that fly at night are guided by stars; by day, polarized light from the sun.
The Culex pipiens is the star, in terms of visibility and West Nile–spreading potential, but despite its star status, it is a boring-looking mosquito. Its alias: the common house mosquito. Its look: brown and gray with relatively unmarked gray legs and a compact antenna. It prefers murky water and likes to drop its egg floats in catch basins; it is the gray rat of mosquitoes. A pipiens prefers a blood meal from a bird and so will come out primarily in the evening, when birds roost in the trees, their breath creating invisible columns of carbon dioxide that the pipiens follow to their meal. If there is no bird in the vicinity, they will find a human. “It’s like steak or a hot dog—if you take the steak away, people will take the hot dog,” says Dickson Despommier, professor emeritus of public health at Columbia and co-host of the podcasts “This Week in Virology” and “This Week in Parasitism.” “For the Culex pipiens, we are the hot dog.”
Of the Aedes vexans it has been said, “They will chew on a rock if they get a chance. They will even go after hubcaps.”
The Aedes solicitan is a salt floodwater mosquito that can travel for miles—an F-14-like creature that could audition for the next installment of Transformers. Striped legs, with a band of white scales around the center of its proboscis. It seems to curl as it stings—a yoga move. This is the mosquito that Dutch settlers in the Meadowlands said was as big as a sparrow.
The Aedes albopictus is the new mosquito on the block—an especially efficient disease carrier also known as the Asian tiger. It likely came to New York from Houston, it is believed, in a shipment of old tires. It is known as a “hard biter.”