Feral Cities (28 page)

But what the Arthropods of Our Homes project reveals is that our homes are more like jungles than we think. Beneath our feet is another, almost unnoticed world. One where unfortunate leaf-hoppers are hunted down by spitting spiders through carpet forests where book lice feast for months on fingernail fragments. A world where fly larvae feed beneath the plughole, cockroaches are terrorized by parasitic wasps, and invasive camel crickets quietly colonize basements.

It's a place we assume we know intimately but is every bit as unknown, fascinating and alive as the outside world.

Just as our houses look different when you're a bug, so do the streets, and for North America's ants the city is a battlefield. For more than 120 years, a war has been raging across the continent as native ants battle against a fierce invader: the Argentine ant. These dull brown ants reached the United States in the 1890s as stowaways on steamships delivering cargo from South America to New Orleans.

They are great at hitchhiking as they are unfussy about what they eat and where they nest, capable of settling down in places as unlikely as trash piles, bird nests, dishwashers, and bee hives. Their adaptable nature has taken them far since they got to Louisiana. By 1907 they had made it to California after hopping trains, and by 1999 they could be found in much of the southern and southwestern United States as well as in isolated patches as far north as Washington State.

For the native ants, the arrival of the Argentine ant was bad news. Very bad news. Argentine ants are warriors and have a zero tolerance policy to other ants in their vicinity. As they advanced, they wiped out other ants, which were slaughtered in the millions by the insect world's answer to Genghis Khan's Mongol hordes.

Only a few native ants have endured. Among them the winter ant, which protects itself from the marauders by spraying a toxic chemical on the ground to form a defensive barrier that delivers a quick and painful death to Argentine ants that try to attack.

But others have been forced into retreat: the wood-dwelling carpenter ant, the seed-eating harvester ant. Even the big-headed ant, which is such a successful invader in its own right that it has been called one of the world's hundred worst invasive species, can't stop it. When Argentine ants attack, big-headed ants abandon their nests and head off like refugees to find a new, safer place to live.

Key to the Argentine ant's ability to crush its opponents is its habit of building enormous super-colonies that house multiple queens and countless workers. The biggest of these colonies is in
Europe. It stretches for thirty-seven hundred miles, starting near the Italian city of Genoa before following the Mediterranean and Atlantic coasts all the way to the northeastern tip of Spain.

Such is the unity of the Argentine ants that if you take one from the European mega-nest and introduce it to the six-hundred-mile super-colony that runs from San Francisco to the Mexican border, it will integrate without a hitch. Most other ants would tear apart any ant from a different nest. Thanks to these super-colonies, Argentine ants have huge numbers on their side, allowing them to overwhelm other ants in battle and find food fast so their rivals go hungry.

But their success is not just down to numbers, super-colonies, or a catholic diet. The other advantage the Argentine ant has is us. Not only have our ships, trains, and trucks transported them around, but also the watered lawns of our cities and towns give them the moisture they need to thrive in otherwise unsuitable environments. As such, the expansion of the Argentine ant empire is closely tied to urban development. The number of Argentine ants increases almost exponentially with the extent of urbanization, and when they stray too far from us, they struggle to continue their otherwise relentless advance.

This ongoing war may seem inconsequential, a case of one ant replacing some other ants, but the fallout of this pint-sized conflict is causing wider damage. Many of the ants that are being exterminated help to disperse the seeds of local plants, and their loss has the potential to threaten the survival of these plants and, in turn, the animals that rely on them.

The California horned lizard is another victim of the ant war. These spike-encrusted reptiles were already struggling because of urban growth erasing their habitat, but the Argentine ants are upping the pressure. The lizard eats ants but needs a wide variety of species to thrive, and as the Argentine ant wipes out the opposition, the lizards are finding it harder to feed themselves.

The Argentine is not the only foreign ant invading the United States. In Texas, another more recent, and potentially more dangerous, arrival is threatening to bring down cities and space missions.

Tom Rasberry was the man who found them. Tom, a pest controller based in Houston, first spotted them in 2002 when a local chemical plant asked him to kill off a bunch of fire ants. They caught his eye because they were unusually small, about the size of a flea, and moved in wayward patterns rather than marching in orderly columns. Odd, he thought, before returning to the task of exterminating the fire ants with pesticide.

A year later the chemical plant called again. Ants, again? asked Tom. Yup, said the facilities manager. But on arriving at the plant he found no fire ants. Instead, the plant was swarming with millions upon millions of the flea-sized ants he spotted the year before.

They were everywhere, pouring into offices, zig-zagging across the parking lot and—most worryingly of all for a chemical plant—flooding into the electronics and causing them to short circuit. What the hell are they? wondered Tom as he tried to blast them out of existence with insecticide. Figuring that he needed an expert's input, he collected some of the ants and contacted Texas A&M University to see if its entomologists could tell him what it was.

The university's bug experts were equally puzzled. They made suggestion after suggestion, but each time they checked the ant didn't match. As the scientists tried to pin down exactly what the new ant was, Tom took to calling it the Rasberry crazy ant. Rasberry after himself, crazy in a nod to their chaotic movements.

The name stuck. Even after it was finally identified in 2012 as the tawny crazy ant
Nylanderia fulva,
the Rasberry crazy ant name refused to go away. “I don't know if I've soiled my family name or brought prestige to it,” Tom told the TV show
Texas Country Reporter.

By then it was clear that the Rasberry crazy ant was a serious problem. They might be small, but they are feisty. They have wiped
out entire beehives as the bees can't stop their assaults because the crazy ants are just too small to sting. Fire ants face much the same problem when the crazy ants attack.

Then there is their habit of invading electronic equipment. The crazy ants like confined spaces and see electrical equipment as a good place to nest or look for food, and—since they are small—they have no trouble at all in getting into everything from desktop computers to cell phones.

Once inside the problems start. One of the ants will, inevitably, create a connection between the tracks of circuit boards and get electrocuted. As that individual dies she releases an alarm pheromone, alerting the rest of the colony to an unspecific threat.

In response to the warning, the dead ant's sisters rally and head to the same spot ready for battle, only to get electrocuted themselves, accelerating the cycle until enough agitated ants get electrocuted to short the entire circuit.

The crazy ant's habit of getting electrocuted until they blow circuits has caused repeated shutdowns at chemical works in the city and panicked NASA, which has hired Tom to stop the ants from entering the Lyndon B. Johnson Space Center and destroying the computers that power its space missions.

But the Rasberry crazy ant is no longer just Houston's problem. They are spreading fast, aided by people inadvertently transporting them in their vehicles. By summer 2008 they had reached Orange County, Texas, on the Louisiana border. Four years later, their presence had been confirmed in Louisiana, Mississippi, and Florida. With its ability to crush even the fearsome fire ant and its potential to wreck computers and electronics in hospitals, airports, power stations, and other critical facilities, the crazy ant may soon make the Argentine ant look like a welcome guest.

Invaders from foreign lands make for good headlines, but not every US city ant came from abroad. One of the most common in North
America is the odorous house ant, known to scientists as
Tapinoma sessile.

In the country it is a meek species that lives a quiet life. The ants found small colonies in acorns that rarely exceed a hundred workers and adopt a rancher lifestyle, protecting aphids from predatory ladybugs and “milking” the aphids for sweet, sugary honeydew.

But, as the Bible passage goes, the meek shall inherit the earth. Or at least the city, for the urban hustle and bustle brings out the wild side of the odorous house ant. On reaching the city, the ants ditch the humble colonies they used to make and embrace the super-colony strategy of the Argentine ant, building networks of nests with multiple queens and more than ten thousand workers that seek to dominate the local ant world.

“It's gone from this rare ant that lived in acorns with one queen to this ant that takes over whole city blocks with hundreds of queens,” says Rob. “My own house is surrounded by them. At first it was thought to be an evolutionary change. Nobody was quite sure what had caused it and it was talked about as a mutant.”

But these are no mutants. The odorous house ant that conquers entire blocks and raids kitchens in search of sugary treats is exactly the same as those tending aphids in the woods.

Instead, they are powered up by the urban world. Buildings offer countless places to nest for an ant small enough to make an acorn its home, and the warmth and protection human structures offer allows odorous house ants to be active all year. There's also more food. Not only are cities full of human food but there are often high numbers of honeydew-excreting bugs like aphids and scale insects too.

Scale insects are strange creatures that act more like mussels or barnacles than insects. After finding a plant to feed on, they stick their proboscis in and use it like a drinking straw to suck the sap. They never move again. Some even shed their legs and antennae after finding a feeding spot, spending their lives drinking sap and covering themselves in protective wax.

Scale insects thrive in cities and one reason for this is the urban heat island effect. In Raleigh the willow oak trees in the hottest parts of the city have way more scale insects than those in the coolest zones. “In the warmest part of Raleigh the ground temperature is six degrees Celsius warmer than the coolest parts. For context that's about as much warming as we expect from climate change by 2070,” says Rob, whose laboratory at North Carolina State University discovered the connection between the city's warmth and scale insect numbers. “What we're seeing in Raleigh is that the trees in those areas have thirteen-fold more scale insects. What is happening is these areas are getting warmer earlier and so speeding up the scales' metabolic activities so that they get bigger earlier in the year.”