If you had to cool down your house three degrees using just paper fans, how would you do it? How many friends would you need to recruit? Where would you and your fanning comrades stand? And even if you were successful, would you be confident that you had cooled down your house as efficiently as possible?
You might have a hard time answering these questions, especially once all the friends you roped in started to bicker. But bees expertly solve these problems all the time.
Bees are persnickety about a lot of things, including the temperature of their hives. In order to produce honey and incubate baby bees, they need to keep their hives at a cozy 36° C (around 95° F). But in warm weather, a cramped space jam-packed with so many fuzzy, vibrating bodies heats up quickly, at which point those bodies stop vibrating because they’ve overheated and died. It takes very precise coordination for bees to maintain the warm-but-not-too-warm environment in which they can flourish.
Fortunately, bees have had many millions of years of evolution to figure out this problem. The solution they’ve come up with is to line up at the hive entrance and use their wings to fan hot air out of the hive. This may not sound all that innovative at first, but bees have it down to an art. The bees collectively sense the temperature and work out how many bees need to fan air out of the hive and how those fanners need to be distributed along the hive entrance.
When humans have to deal with stuffy, sweltering buildings, our solution is often to toss air conditioners at the problem. But our non-bee brains don’t innately know the best placement for air conditioning units, and our conventional building ventilation systems aren’t very adaptable to different environmental conditions. We probably aren’t cooling our buildings as efficiently as we could if we were able to think like bees.
Orit Peleg, an assistant professor of computer science in the BioFrontiers Institute at CU Boulder, thinks that humans can learn to be more efficient if we understand the way bees cool down their hives.
“This is how the bees are doing it using a minimal amount of energy,” she says. “Can we think about smarter ventilation systems for buildings that also move around depending on the environmental conditions, the position of the sun?”
Peleg is an expert at building math-based computer models to simulate the behavior of animals who act in groups. These models are sets of equations in which you can plug in numbers that describe environmental factors to calculate numbers that describe animal behaviors.
During her postdoctoral work at Harvard University, Peleg worked with Jacob Peters and Lakshminarayanan Mahadevan, a post-doctoral researcher in the Department of Organismic and Evolutionary Biology and a professor in the Department of Physics at Harvard, respectively, to observe fanning bees at different temperatures. The ultimate goal was to turn their observations into equations that could predict how bees will fan at different temperatures.
Peleg and her colleagues built an equation, recently published in the Journal of the Royal Society Interface, where you can plug in the temperature of the area around a hive and calculate the rate at which individual bees head to the entrance and start fanning. They can use these rates to calculate the velocity of the airflow into the hive.
In order to build equations that accurately model the behavior of real-life bees, Peters monitored the entrance of a beehive over the course of many days. He was able to count how many bees were fanning and see how those fanning bees were clustered across the hive entrance. He was also able to track the temperature and the velocity of airflow at different spots along the hive entrance.
Once the group had a lot of experimental data, they could start building a mathematical model to explain it. They started off by thinking about what needs to be true for the bees to behave the way they do, which led to four mathematical assumptions.
The first thing that needs to be true for these equations to work is that the bees are facing into the hive and fanning air out, as European honeybees (Apis mellifera) used in most honey production do. “The second assumption is that bees turn on their fanning behavior when it gets warm,” explained Peleg. “And that’s, by the way, based on work from Mike Breed in [the Department of Ecology and Evolutionary Biology at CU Boulder].” The third assumption is that the volume of the hive is conserved –as bees pump hot air out of the hive, cooler air from outside the moves in to replace it. The last assumption is that fanning bees organize themselves to minimize friction between opposing airflows, which mostly means that they cluster at one side of the hive entrance so that there’s only one place where air being pumped out of the hive has to fight against the air rushing in.
After Peleg and her colleagues had determined the assumptions they needed to consider while building their model, they just needed to build an equation around the assumptions and then, as Peleg explained, “compare it to the experiments and go back and forth. If the experiments and the model give a similar result, then we probably understood something about system.”
At the end of this process, Peleg had a set of equations where you plug in the temperature to calculate the average rate at which bees start fanning, which you could then use to calculate the density of fanning bees. You could use that number, along with the length of the hive entrance and some terms to describe the conductivity of the hive and the friction between air moving in different directions, to calculate the velocity of airflow into the hive.
One of the cool things this mathematical model confirms is that individual bees start fanning at all different temperatures. If all the bees started fanning at the same temperature, this ventilation system wouldn’t work – the hive would keep heating up until it hit a critical temperature, at which point all of the bees in the hive would switch on their fanning activities at once. Everybody would be fanning and trying to line up at the entrance; the whole thing would be a mess. But since different bees have different temperatures at which they start thinking, “Gee golly it’s hot – I’d better start fanning,” the hive will have a few bees fanning when it’s slightly too hot out and more fanning as things get more sweltering.
If we took some tips from the bees, we could think about systems where small air conditioning units move around so they stay in the shade and only pump in cool air. We could consider friction between air moving in different directions while designing ventilation systems. And we could set up multiple air conditioning units turn on at different temperatures, just like the bees.
“This is one of the reasons that I like studying animals,” Peleg explained. “They’ve had so many years of evolution to perfect some of these tasks. So effectively they have a very intuitive understanding of physics and decision making, information processing, and so on. For me, it’s really hard to understand, but they just do this. So we’re looking at the kind of optimal solutions that they come up with.”
So before you alienate all your friends by asking them to fan the hot air out of your house, spend some time watching how bees air condition their hives – or better yet, recruit the bees to do it for you.
By Graycen Wheeler
Science Buffs 