Feral Cities (29 page)

For the parasitic wasps that target scale insects this is a problem. “Because the parasitoids experience multiple temperatures when they fly around, their metabolism doesn't speed up as much, so by the time they go to attack the scales, the scales are already really big and so they can reproduce more,” says Rob.

“It looks like these patches of heat are super important in affecting what's going on overall. It's interesting for us because, in general, we suck at making good predictions for what to expect with global warming, but in cities you have this terrific experiment where we've essentially simulated what we think conditions will be in 2070, and that's why we're looking at New York.”

New York, and Manhattan especially, has become an object of fascination for Rob's laboratory. “New York's so cool,” he says, eyes lighting up at the very thought. “The road medians on Broadway are super hot. They are surrounded by all these buildings and all the sunlight bounces off the buildings and can't get back up, so the ground heats up. These medians are like a foot of dirt on top of the subway and are this kind of fantastic futuristic ecosystem.

“Sixty percent of everybody now lives in cities, 70 percent is coming faster than anybody thinks, and the remaining 30 percent live in places that are not nearly so rural as we think. So in that
regard the experience of walking down a street in Manhattan or Tokyo or some monster city in China is way more like our future experience of nature will be.”

To find out what this ultra-urban future might mean, scientists from Rob's laboratory have been surveying the ants living in the road medians of Broadway to see what life might be like in a hotter future. Post-doctoral scholar Amy Savage has been leading the study. When we meet she is in the midst of crunching the data she has gathered after months of visiting New York and scrabbling around in the medians with her aspirator at the ready.

You must have gotten some funny looks doing that, I say. She nods. “One time I scared this woman. She was sitting at one of the tables on the median and looked up and there I was. I wasn't paying attention to her and she was like, ‘Oh! What are you doing?' I said, ‘I'm studying the ants.' Now sometimes people ask why and that's great because you can then talk about how ecology is happening everywhere, but this lady was like, ‘All right. Whatever you want.'

“Another time a guy said, ‘We don't like people being in the medians because they will hurt the plants but also because we put rat poison down every morning.' I was like, ‘Oh. I've been sucking up the soil with my aspirator.'”

When not being interrupted by New Yorkers or sucking up poisoned soil, Amy has discovered some unusual things about the ants on Broadway. First, they are not the same ants as those living in the forested areas within city limits. “I thought we'd find everything that is in the medians would be in the parks and urban forests, but that's not what we're finding,” she says. “We find things that are in the medians that you never see in the forest. The next step is to ask why, and so we're thinking about the idea of stress in the habitat and whether there's a relationship between stressful conditions and species.”

Another curiosity is that the Broadway ants have different food preferences from other ants. “The story with ant diets is usually proteins versus sugars, and then there's some recent work showing
that salty food is a requirement for some ants, so those ants do really well by roads because there's so much salt there.”

Given this, Amy didn't expect to find anything unusual when she got around to testing the New York ants' food preferences. She set down five liquid baits: water, sugar water, salt water, an amino acid solution representing protein, and, for fats, some extra virgin olive oil. The water and olive oil were there as controls; it was the proportion of sugar, protein, and salt the ants went for that she wanted data on. The ants living in the parks behaved as expected, sipping at the sugar, protein, and salt options but—for the most part—living up to ants' reputation as sugar fiends.

But the Broadway ants didn't conform. “The pavement ants in the park, over 90 percent of the time they went for sugars, but in the medians there was this complete shift to the extra virgin olive oil. It wasn't just this one species. It happened with all the species. They all had this flip where they went for the fats in the olive oil. In the median almost all they went for was the oil.”

Amy thinks the shift is because of the lack of other arthropods living in the medians and the steady supply of sugar passersby provide in the form of spilled soda and discarded New York-style pizza. “If you go to those medians on Broadway and turn over a rock, any rock, there are isopods everywhere: roly-polies, millipedes and these beetles called rove beetles. All of these species are really good at avoiding ant predation. So we have this hypothesis that median ants are just really hungry because there are few prey species available. They are able to get a lot of sugars from whatever is discarded, but if you think of it in evolutionary time, ants did not grow up with extra virgin olive oil, so they got their fats from grasshoppers and things like that, but there aren't any of those really fatty insects in the median.”

The shortage of fats could, she says, be making the ants more aggressive predators, which might explain why the ants of Broadway are outcompeting rats for food. The ants' ability to outcompete the rats was first noticed when another researcher doing an unrelated
study on the New York medians laid some traps for the rodents. “He was trying to trap rats with a trap with bait in it and had a heck of a time on the medians because the ants ate all of the bait before the rats could get to it,” says Amy. “You think that an individual rat is so much bigger than an individual ant but, really, it's more reasonable to think of ants as a colony and the biomass of a colony can be big, although I'm not sure it would be as big as a rat's biomass. But ants are also super-efficient and active all the time, while rats are more active at dawn and dusk.”

Rats might loom larger than ants in the minds of New Yorkers, but on these futuristic streets the ant may yet prove to be the real king of Manhattan.

Paul Doumer arrived in Hanoi in 1897 burning with ambition. Fresh from a failed attempt to introduce an income tax while serving as France's finance minister, the Radical politician saw his new role as governor-general of Indochina as a chance to make his mark.

Until then, the French Empire had taken a hands-off approach to the colony. Previous governor-generals preferred an indirect approach to running the territory, but under Doumer that all changed. As far as he was concerned the place needed civilizing. He compared his mission to that of the Romans conquering the barbarians, and saw it as his duty to introduce the people of Indochina to the superior culture of France.

Doumer was ruthless in achieving this zealous goal. He deposed the local emperors, replacing them with figureheads who would do his bidding, and transformed Indochina's government into a highly centralized bureaucracy run almost entirely by the French. Keen to make the colony profitable, he imposed harsh taxes on the people and forced the nation's peasants into slavery so that a network of
highways, bridges, canals, and railroads could be built. To cap it all off, Doumer's government encouraged the Vietnamese to get hooked on opium, even opening stores to peddle the drug so it could reap the profits from creating a nation of addicts.

Doumer's actions caused deep resentment among the people of Indochina and helped sow the seeds for the Vietnam War. But as far as France was concerned he was doing fantastic work, and Indochina became the toast of the French Empire.

Hanoi was to be his crowning glory. He envisaged turning the ancient Vietnamese city into the epitome of an orderly, modern metropolis. To start the transformation, he built a whites-only residential neighborhood of luxurious villas and wide, tree-lined avenues connected by a thoroughly modern grid road network.

Naturally, this flashy new quarter of Hanoi was supported with a state-of-the-art sewer system. It was a far cry from the creaking drainage system the Vietnamese lived with, which did little more than pour raw sewage into the Red River and flood the streets with human waste in the monsoon season. The sewer was crucial to the new quarter. The role that rats and fleas played in the spread of bubonic plague had just been discovered, so the new whites-only sewers were designed to protect the French residents of Hanoi from an outbreak.

All was going well until the residents started reporting that rats were entering their homes through the indoor plumbing. It turned out the new sewers were infested with rats, which found them an ideal place to live thanks to the lack of predators and the convenience of having an underground network of tunnels to roam. Shortly after came the first cases of bubonic plague in the French quarter.

Unwilling to have his grand plan upset by mere vermin, Doumer ordered the rats be exterminated. So began the great rat massacre of Hanoi.

The massacre began in late April 1902 when the government sent in teams of Vietnamese rat catchers, who were paid in line
with the number of rats they killed. It was dangerous and thankless work. The sewers were cramped, dark, and filthy places that housed not only rats but also spiders, flies, and snakes. Despite the challenge, the first week was a huge success. The rat catchers emerged from the sewers with thousands upon thousands of dead rats.

By early May nearly eight thousand rats had been killed, and the haul kept rising. By mid-June the rat catchers were bringing more than ten thousand dead rats to the surface every day. On one day their haul even topped the twenty thousand mark.

Not that this pleased the French residents, who now found their manicured streets were full of stinking Vietnamese rat catchers dragging around hundreds of dead rats. Soon the colonists were complaining about having to put up with the sight and smell of the rat catchers.

The rats, however, were down, not out. They quickly learned to avoid the rat catchers, and the numbers being caught began to plunge. At the same time the rat catchers were getting fed up and started demanding more money. After repeated strikes their pay was quadrupled, but by then they were struggling to deliver results. The rats, now wise to the rat catchers, were breeding faster than they could be caught.

Doumer's administration decided that if the rats were going to be defeated, they needed an army. So it told the people of Hanoi it would pay a bounty of one cent for every dead rat. Keen not to have mountains of dead rats dumped at their offices, the French told people to just bring in the tails.

The French imperialists must have felt rather pleased with themselves then, when people began turning up with thousands upon thousands of rat tails. But their glee was short-lived. Soon reports came in of tailless rats roaming the city. It turned out residents were chopping off the tails but letting the rats go free so they could keep breeding. Some enterprising people had even started breeding captive rats so they could profit from the tails.

Together the cunning of the rats and the people of Hanoi won
out. Thwarted, the French conceded defeat and scrapped the extermination program, and soon it was back to life as usual for the rats beneath the city.

As Doumer's doomed extermination plan confirmed, rats are part and parcel of city life, immovable and undefeatable. Rats have conquered cities the world over. Some have more, some have less, but almost no city is rat-free.

While Southeast Asian cities like Hanoi are home to many species of rat, the streets of Europe and North America are dominated by just two: the black rat,
Rattus rattus,
and the brown or Norway rat,
Rattus norvegicus.

The black rat, also called the ship's rat, is the rarer of the two, but once upon a time it ruled the city. These velvet-furred rodents have long been implicated as the vehicles that spread the plague-carrying fleas that unleashed the Black Death, the twelfth-century pandemic that wiped out more than one-third of Europeans.