The World Without Us

At the same time, any mosquitoes still bereaved by our passing will be consoled by two bequests. First, we’ll stop exterminating them. Humans were targeting mosquitoes long before the invention of pesticides, by spreading oil on the surfaces of ponds, estuaries, and puddles where they breed. This larvicide, which denies baby mosquitoes oxygen, is still widely practiced, as are all other manners of antimosquito chemical warfare. They range from hormones that keep larvae from maturing into adults, to—especially in the malarial tropics—aerial spraying of DDT, banned only in parts of the world. With humans gone, billions of the little buzzers that would otherwise have died prematurely will now live, and among the secondary beneficiaries will be many freshwater fish species, in whose food chains mosquito eggs and larvae form big links. Others will be flowers: when mosquitoes aren’t sucking blood, they sip nectar—the main meal for all male mosquitoes, although vampirish females drink it as well. That makes them pollinators, so the world without us will bloom anew.

The other gift to mosquitoes will be restoration of their traditional homelands—in this case, home waters. In the United States alone, since its founding in 1776, the part of their prime breeding habitat, wetlands, that they have lost equals twice the area of California. Put that much land back into swamps, and you get the idea. (Mosquito population growth would have to be adjusted for corresponding increases in mosquito-eating fish, toads, and frogs—though, with the last two, humans may have given the insects yet another break: It’s unclear how many amphibians will survive chytrid, an escaped fungus spread by the international trade in laboratory frogs. Triggered by rising temperatures, it has annihilated hundreds of species worldwide.)

Habitat or not, as anyone knows who lives atop a former marsh that was drained and developed, be it in suburban Connecticut or a Nairobi slum, mosquitoes always find a way. Even a dew-filled plastic bottle cap can incubate a few of their eggs. Until asphalt and pavement decompose for good and wetlands rise up to reclaim their former surface rights, mosquitoes will make do with puddles and backed-up sewers. And they can also rest assured that one of their favorite man-made nurseries will be intact for, at minimum, another century, and will continue making cameo appearances for many more centuries thereafter: scrapped rubber automobile tires.

Rubber is a kind of polymer called an elastomer. The ones that occur in nature, such as the milky latex extract of the Amazonian Pará tree, are, logically, biodegradable. The tendency of natural latex to turn gooey in high temperatures, and to stiffen or even shatter in cold, limited its practicality until 1839, when a Massachusetts hardware salesman tried mixing it with sulfur. When he accidentally dropped some on a stove and it didn’t melt, Charles Goodyear realized that he’d created something that nature had never tried before.

To this day, nature hasn’t come up with a microbe that eats it, either. Goodyear’s process, called vulcanization, ties long rubber polymer chains together with short strands of sulfur atoms, actually transforming them into a single giant molecule. Once rubber is vulcanized—meaning it’s heated, spiked with sulfur, and poured into a mold, such as one shaped like a truck tire—the resulting huge molecule takes that form and never relinquishes it.

Being a single molecule, a tire can’t be melted down and turned into something else. Unless physically shredded or worn down by 60,000 miles of friction, both entailing significant energy, it remains round. Tires drive landfill operators crazy, because when buried, they encircle a doughnut-shaped air bubble that wants to rise. Most garbage dumps no longer accept them, but for hundreds of years into the future, old tires will inexorably work their way to the surface of forgotten landfills, fill with rainwater, and begin breeding mosquitoes again.

In the United States, an average of one tire per citizen is discarded annually—that’s a third of a billion, just in one year. Then there’s the rest of the world. With about 700 million cars currently operating and far more than that already junked, the number of used tires we’ll leave behind will be less than a trillion, but certainly many, many billions. How long they’ll lie around depends on how much direct sunlight falls on them. Until a microbe evolves that likes its hydrocarbons seasoned with sulfur, only the caustic oxidation of ground-level ozone, the pollutant that stings your sinuses, or the cosmic power of ultraviolet rays that penetrate a damaged stratospheric ozone layer, can break vulcanized sulfur bonds. Automobile tires therefore are impregnated with UV inhibitors and “anti-ozonants,” along with other additives like the carbon black filler that gives tires their strength and color.