Feral Cities (27 page)

A good proportion of the flies are phorid flies, also known as humpback flies. They are tiny. The biggest are no more than six millimeters long. The smallest is
Euryplatea nanaknihali,
the world's smallest known fly. It measures a mere two-fifths of a millimeter long.

Another famous phorid fly—well, famous among entomologists at least—is
Megaselia scalaris.
“It is probably the most prolific insect on Earth,” says Matt. “It seems to be everywhere around the world. It has even been found in an Antarctic research station. It feeds on everything: plants, fungus, paint, shoe polish. It's parasitic too. They are insane. Basically, if they can eat it, they will eat it.”

And, as you might imagine for an insect that eats shoe polish, it doesn't care where it ends up. “Some were found alive in a snake that was preserved in formaldehyde in a jar,” says Matt. “I've found papers about them infecting the lungs of a python that had pneumonia. They were in there eating the bacteria.”

Other common household invertebrates are equally unfussy about what they eat. Not least, the wingless silverfish that often live in bathrooms, where they eke out an existence feeding on everything from wallpaper and shaving foam to dandruff and shampoo. “It takes silverfish years to mature because they eat things like glue, paper, and leather,” says Matt. “They will eat really weird things that you don't think are digestible.”

Insects like silverfish and book lice have a long history of living with us, says Michelle. “Book lice are these tiny little things and we see them in almost every house. An insect leg or a hair can feed a book louse for months. They are dwarfed by mosquito legs. They
are not parasitic—they live off your detritus. They were probably doing that with our ape ancestors, so it goes back millions of years.”

While some household arthropods date back thousands of years, others are more recent colonizers. “Some of them are a reflection of how our lifestyles have changed,” she says. “So in living quarters of these houses in ancient Egypt there were dung beetles because human and animal waste was more closely associated with houses back then, whereas now we have got new species that are associated with indoor plumbing.”

“I once found a dung beetle in my house,” Matt volunteers. “Not sure what that says about my house.”

One more of these modern arrivals are drain flies, a group of flies whose fuzzy fur makes them look like mini-moths. As their name suggests, they find the drains of modern homes a good place to live. Their larvae live inside the pipes, munching on the moist slime that builds up until they metamorphose into flies that live for a couple of days at most.

Or, at least, that is what they seem to be doing. Truth is, no one's actually done the science. “It looks like they are feeding on microbes in drains, but nobody's ever studied their biology or their evolution,” says Rob Dunn, the associate professor of biology at North Carolina State University who dreamt up the Arthropods of Our Homes project with Michelle. “There does not appear to be a single scientific paper on them, other than enough to know that they exist.”

The roots of the Arthropods of Our Homes project lie in another of Rob's studies, one that sought to find out what microbes live in homes. Like many of his studies, the microbes project was powered by citizen science with members of the public volunteering to have their homes swabbed for bacteria and other microscopic organisms.

After gathering all the samples from people's homes, Rob needed to give his army of volunteers something to do while he and
his team pursued the time-consuming process of figuring out what bacteria they had found and analyzing the results. So he created a checklist of arthropods that people might find in their homes, e-mailed it to the volunteers, and asked them to report back on what they found in their game of creepy crawly bingo. One of the insects on the list was the camel cricket, a nocturnal brown cricket that gets its common name from its humped back. “I expected that people would find it as they sometimes turn up in basements, but that it wouldn't be that common,” says Rob.

But when the results came in, something was up. The numbers saying, ‘Yes, I have a camel cricket' were much higher than expected. Not only that, they were clustered geographically, rather than being dotted randomly across the country. Rob was puzzled. Maybe, he thought, people are mistaking something else for a camel cricket.

“There was this super-weird distribution. What we understood about these things is that they are a cave species and move into basements because they are like caves and that these crickets are all over North America. But when we mapped the results it was this weird smear on eastern North America. So we sent another e-mail saying send us a picture of it, because it's possible people were looking at a squirrel and thinking they were camel crickets or whatever.”

When the photos came back, it became clear that the volunteers weren't mistaken. They had indeed found camel crickets in their basements, just not the one anybody expected. “Almost all of them turned out to be this invasive Japanese camel cricket. It looks similar but is a bit bigger and hoppier. It was known to be in the United States, but no one knew it had taken over basements across North America. I even had them in my own basement and didn't realize they were the Japanese ones.”

The most visible difference between the two species is color. The back of the US camel cricket has a mottled appearance while its Asian counterpart has dark and light brown stripes. Japanese
camel crickets also lack the spikes that are on the hind legs of the American species. These may sound like superficial differences, but they are just the obvious signs of the huge evolutionary gulf that exists between the North American and Asian camel crickets. “There's probably about twenty million years' difference between them. It's like thinking you have cats in the basement and you go and look and you realize it's wild African dogs. They are that different,” says Rob.

After finding the surprise camel cricket lurking in the nation's basements, the idea for a deeper investigation into what is living in houses quickly took shape. Since then, Michelle, Matt, and the rest of the team have searched miles of baseboard and more than three hundred rooms in fifty Raleigh houses and collected more than ten thousand bugs.

Each house takes several hours to search and the researchers spend much of their time crawling around on the floor, which is why Matt wears kneepads on the job. “The longest was seven hours and that was me alone in an over three-thousand-square-foot, hundred-year-old house with three floors,” says Matt, as he probes the utility room of the house, sucking up insects caught in the spider webs on the ceiling.

Even then, the searches are not as thorough as they could be. To protect people's privacy and save time, the team don't move furniture, check cupboards, or look behind fridges. They also stopped looking in light fixtures. “At the beginning we did, but light fixtures have as much diversity as a full house,” says Michelle.

Perhaps surprisingly, people were more than happy to open their homes to the bug hunters. In fact, many were desperate to have them visit. “People were petitioning. They were like, ‘How much can we pay you to come to our house? We've got the craziest bugs ever,'” recalls Matt. “It was like a competition, people saying, ‘I've got more bugs than everybody else.'”

Yet no matter how unusual people think their creepy crawlies are, the reality is the bug count doesn't change much from home
to home. Each property delivered a haul of about one hundred species. What's more, it doesn't seem to matter how much pesticide you spray or how often you clean. “You can't do anything about it,” says Michelle. “It doesn't matter how much you spray. We are going to find a ton of stuff in your house if we come looking for it.”

The volume of bugs in homes even surprises eminent biologists. Michelle tells me about the time that the famed American biologist and the world's foremost ant expert E. O. Wilson paid a visit to the North Carolina Museum of Natural Sciences. While he was there, Michelle showed him the bugs from one of the houses.

“Is this all from a house in a wood that kept its windows open?” he asked.

“No,” replied Michelle. “This was a house that had a weekly cleaner. This is typical.”

While regular cleaning and pesticide spraying doesn't seem to make much difference to bug diversity, having a dog does. Houses with dogs have consistently fewer species. Michelle's not sure why. It might be that dog owners vacuum more or that pets disturb the insects more, she guesses. But, for all we know, the pooches could be eating them.

First floor rooms boast the biggest range of arthropods, thanks to the regular influx of insects from the outside that either fly or get blown in by accident or are lured indoors by our lights. The attraction of artificial light explains why insects like sap-sucking leafhoppers are found in home after home.

For the bugs that spend their lives in our houses, the constant arrival of accidental visitors is a boon. “All those insects that come in accidentally get eaten by the spiders and other things,” says Matt.

Spiders are especially well suited to life indoors, he adds. “There are plenty of spiders that live in homes and love traveling around homes. They are really good at living in dry environments because they can close up their bodies really well so that they don't lose a lot of moisture. That's why spiders can live in such arid regions.
They can also live for months without eating, a year without eating. They just have to be patient and see what comes along, so living in a house is fine for them, almost as much as living outside.”

One spider that shows up regularly is the spitting spider
Scytodes thoracica.
One in ten of the Raleigh homes had these arachnids, which have bodies about the size of a grain of rice and sometimes live behind light switches. They are pale yellow with black splotches that become rings of black on their needlelike legs.

These spiders don't spin webs. Instead they are hunters that roam our houses in search of prey. Since their eyesight is poor, they rely on the sensitive bristles on their front legs to “smell” prey and so go on the prowl with their front legs held up so they can taste the air. After smelling a target, they close in and stop a couple of centimeters away before taking aim and shooting a mix of sticky webbing and venom that paralyses their victim. They also use this poisonous glue to defend themselves from predators and, sometimes, potential mates they mistook for a meal.

“The spitting spider has traveled around with us too. It's come from Europe,” says Michelle. “Like a lot of these things they are covertly moving all over the planet, going for global domination without us having any idea.”

Another, larger alpha predator of the home is the house centipede. Michelle calls it the “lion of the home” but Disney won't be making an animated picture about it anytime soon. Imagine all the traits about arthropods that freak people out and then put them together into one creepy crawly. Chances are you've pictured something close to a house centipede.

They can grow to two inches long but their fifteen pairs of long, spindly legs make them look twice as long. The last pair of legs is extra long, matching their drawn-out antennae and making it hard to tell its back from its front. Close up its face reveals a pair of sharp fangs for pincering prey and large jaws that look well designed for crunching hard exoskeletons. They move fast too. It seems like a creature that could cause nightmares and, judging by the panicked
commentary on YouTube videos posted by those who have encountered these beasts in their homes, they probably do.

The house centipede is widespread, found across North America, Europe, and Asia, yet it remains one of the more mysterious members of the household ecosystem. House centipedes are understudied beasts. In the lab they eat everything from wood lice and cockroaches to earwigs and bees, but little is known about their behavior in our homes.

“If people really don't like an arthropod, we study it,” says Rob. “People really don't like roaches—they are viewed as purveyors of disease, so we know a reasonable amount about them. Then, you've got bed bugs. Bed bugs are pretty well understood again. These things that really get to us, we will eventually learn about them in order to kill them. But this stuff that's there but neither deadly nor likable, nobody funds that. The house centipede just fits in this place where no one touches it.”

And that's the crux when it comes to life inside our homes. No one is really studying anything more than the pests.

For all anyone knows, the bug life lurking in the freestanding houses of Raleigh are oddities. Would apartments and offices have more or less insects? Is the bug diversity in a house in the suburbs of Portland, Lisbon, or Perth different from that in Raleigh? We're a long way from knowing answers to these basic questions, let alone how all the bugs that live among us interact with each other.