How ants play the real estate market

The more a Manhattanite dislikes her apartment, the more time she’ll put into searching for a new one.

A rock ant does the same thing – and with the noisy input of hundreds of brethren, no less.

A new paper published in the journal Biology Letters reports that rock ants budget their resources toward finding a housing upgrade depending on how good or bad their current housing is. The research highlights the complex calculations that rock ant colonies are capable of making – calculations that stun scientists and casual observers alike, since these tiny insects do it all without a leader.

Rock ants, or, Temnothorax albipennis, belong to the Temnothroax genus that includes some 346 species. Since their colonies are small, at just 50 to 600 individuals, these European ants have been convenient, popular research subjects, along with a few of their North American cousin species, like the so-called acorn ant.

Orange-brown colored, with a glassy-looking rear like an amber bobble, rock ants are small at just two to three millimeters. Somewhat counter-intuitively, these bantam beings don’t live “blink of an eye” lives, but boast lifespans up to several years long. A colony’s queen, a colossal and winged ant, can live up to a decade.

Rock ants, of course, will find a new home if their present one is destroyed – in the event of, say, a small child testing his or her dominion over everything smaller that he or she. But ants are not so complacent that they’ll bed down in just anything, so long as it’s not on the bottom of a shoe.

No, these ants prefer to climb the property ladder.

“Rock ants will always emigrate once their current nest is no longer considered hospitable,” says Carolina Doran, a PhD student at the University of Bristol's School of Biological Sciences and the lead author on the paper.

“Interestingly they also emigrate if they find a new nest that is sufficiently better then the one they are currently in,” she said.

And, like Manhattanites culling listings for apartments with elevators, laundry rooms, and – hey, why not? – splashes of exposed brick, ants are fussy property buyers. Ants prefer dark nests to bright ones. They like entrances small enough that intruders will have a tough time intruding. They want to know the square footage and how high the ceilings are.

“Ants know exactly what they like,” says Ms. Doran.

But unlike a Manhattanite eschewing plum listings in outer Queens for teaspoon-sized studios in the East Village, rock ants are prepared to travel far to find this prime real estate. In a 2009, a team of researchers also from Bristol’s Ant Lab traced ants’ whereabouts during a house hunt and found that the tagged ants would choose the best house even if it was nine times further from their current home than was a less swanky spot.

Still, finding a new place and moving is a lot of work, for ants and New Yorkers alike. So, how do ants budget their resources toward plying the real estate market? Under what circumstances are ants more likely to invest time and energy into culling the local area for better digs?

In September 2011, the new paper's authors, a team from the Ant Lab at Bristol, collected 15 ant colonies from Dorset, UK. The colonies were each monitored in five different artificial nests ranked in quality on a scale of one to five. They were also allowed to roam in an enclosed area outside each nest.

The researchers wanted to know how many ants the colonies sent outside the nest at each of the five locations. In the experiment, this number was an indicator of how much each of the colonies was budgeting toward finding a new place: the more ants outside the nest, the more urgent the colony’s search for superior digs.

The results were as predicted: when the nest was to the ants’ liking, the colony sent out fewer bantam real estate agents to comb the area for a better investment, the researchers found.

“It’s a satisfying result,” said Stephen Pratt, a researcher at Arizona State University who was not involved in the research. The findings are in keeping with his previous work showing that a cousin of the rock ant will allocate more house hunters when their circumstances are extremely bad versus just alright, he said. This new paper suggests that ants also make these calculations when faced with just subtle differences between home qualities, he said.

But how does this all work? How does a group hundreds strong ever manage to pull off this adventure in house hunting? To anyone who has ever tried to organize a gathering of more than two people, the idea that a swarm of insects can agree on how many scouts to send out, which home is the best home, and when to close house and teeter off to the next nest is as befuddling as it is shaming.

“The outstanding question about ants (and other systems like ant colonies) is how do simple local interactions produce complex global adjustments, without anyone directing the behavior or making any overall decisions about what needs to be done,” says Deborah Gordon, a specialist in ant collective behavior at Stanford University who was not involved in the research, in an email.

How a colony manages to send out the appropriate number of scouts is often simplified as a mathematical problem, says Dr. Pratt. At all times, ants must decide how to use their time – to tend to the brood? To gather food? Or, to scout for a new home?

“Every ant is a potential scout,” he said (with the exclusion of the queen and the brood).

The more inadequate the home, the higher the odds that an ant will notice the holey roof and will chose to go look for a new place, says Pratt. This means that, the worse the house, the more ants will make the same choice to house hunting. Certain factors, like the fact that young ants are extremely unlikely to take on house hunting, even if a human child is prodding at their home, ensure that not all of the ants will abandon the nest at once, he said.

But once a bunch of ants go off looking for a better home, it’s possible that more than one ant will find a nest they prefer to the old one. So, let’s say that two ants both find nests they believe are suitable. Now, neither of the ants is even aware that there is another option. Each knows just this: it has found a nice home, and it would like its colony to come live there.

Next, the two ants return to the nest to get their compatriots. First, in what is called “tandem running,” the scouts lead recruited ants to their new, little worlds. The recruits either like the nest and stay there, or they look askance and toddle home. At some point, the population at one of the new places will reach a certain number, called a quorum. Once this number is reached, the ants get bolder about recruiting the rest of their group, simply scooping up their queen, larvae, and brethren and carrying them to the new home.

Studies have shown that the winning spot is usually the better choice. That’s because, probabilistically, the place that reached quorum first is the one to which an ant had an easier time recruiting than did the other scout.

It’s also more likely that a colony will end up at the better home when decisions are made this way as opposed to coming from a leader, says Pratt.

“If this were a human colony, the scouts would file a report, and some leader would compare them and organize a migration. This is definitely not what ants do at all,” he said.

“The colony as a whole can do a lot better than any one ant can do,” he said. “A colony averages the outcome of a lot of not very good cognitive processes into one good choice.”

Of course, this doesn’t always work, said Pratt. Though ants are extremely capable of choosing the subtly better option of two homes, studies have shown that they are less likely to end up in the better one if the difference between the two options is extreme, he said.

In other words, if the choice is between two identical apartments, but one has some nice exposed brick, the ants will close out on the trendier apartment. But, if the choice is between a basement apartment across from a firehouse and a Fifth Avenue penthouse, the ants will set up in the basement.

“There’s a disadvantage to deciding as a colony,” says Pratt. “No one ant knows the big picture and they’re all just following positive feedback. Sometimes, by chance, it can go the wrong way.”

Altogether, much is still unknown about ants’ escapades in moving, says Pratt. While researchers have a rolodex of traits that ants look for it a good home, it’s not clear how ants weigh each of these traits. And in the event that one ant does visit two home options and compares them – this happens sometimes – it’s not clear how this ant’s superior, individual knowledge is weaved into the collective decision making process.

However ants do it, it’s sure to put humans to shame.