Bee Eye in the Sky
Air Date: Week of February 18, 2000
It seems that bees have a novel way of gauging how far they must fly to get to their favorite dinner spot. Guest host Laura Knoy speaks with an Australian researcher who says that these optical odometers could one day help us design hi-tech flying machines, including ones used for spying.
KNOY: The U.S. military is going to the bees to learn how the better to see you. The Pentagon is helping fund research that may someday lead to tiny flying spy machines based on insect navigation. It's long been known that honeybees use body language to direct nest mates to sources of pollen and nectar as far as six miles away. It's called a waggle dance, and the longer the dance, the further away the food. Now scientists think they've discovered just how honeybees measure these distances. The research effort is led by Mandyam Srinivasan, a biologist at Australia National University. Professor Srinivasan joins us now from the studios of the Australian Broadcasting Corporation in Canberra. Thanks for taking the time today, professor.
SRINIVASAN: Thank you very much.
KNOY: So, tell me, just what does the waggle dance look like?
SRINIVASAN: A worker bee that's found a good source of nectar comes back to the hive, and then she basically shakes her hips from side to side. And it turns out that the duration of this waggle, measured in seconds, for example, is a measure of how far away the food source is. And the direction in which this waggle part of the dance occurs tells the other bees about the direction in which they should fly to get to the food source.
KNOY: You've written that the honeybees use something called an optical odometer. Now what's that?
SRINIVASAN: When this bee comes back, this bee has to transmit the information about the distance to the food source to the other bees. And the question that's been puzzling us and several other people in the past is, how does she figure out how far she's flown? The cue that they seem to be using is really, they're looking at the world as they fly to the food source, and they're looking to see how much the world, how much the image of the environment has actually whizzed by on their eyes. And if there's been a lot of image motion on the eye, they infer that they've flown a long distance. And if the world hasn't moved very much at all, they infer that it's a very short distance. So, this odometer now turns out to be visual, optically-driven, and not driven by, you know, how many wing beats you've made or measuring even the time taken to get there.
KNOY: Now, how did you figure this out?
SRINIVASAN: We took a tunnel and placed it right at the entrance to the hive. The inside of the tunnel was lined with something like wallpaper, a randomly-textured black and white checkerboard. So we put a feeder at the end of this tunnel, so bees had to fly, get out of the hive, and fly into this tunnel a distance of six meters to find a reward of sugar water, and then fly back to the hive. And then we looked at the dances, and to our surprise, when the bees danced they were signaling not six meters, but a distance of 200 meters. And for some time we really couldn't understand why. And then we reasoned that maybe what was happening was that, because the walls of the tunnel are very close to the bee, I mean the tunnel is very narrow, the environment appears to move by on the eye very rapidly. For example, if you were to fly from Boston to New York and you look at the ground, the ground wouldn't move very much at all and you wouldn't think you've traveled very far. But if you drove from Boston to New York, you'd see a lot of image motion and you do get the impression you've traveled a lot. So maybe that's what's happening with the bees as well. Well, we tested this idea by taking away this textured wallpaper, just replacing the walls and the floor with just a plain blank white lining, and then looked to see what the bees did when they flew the same distance. And then, to our surprise, again, they showed zero. They showed no distance at all. It's as though their odometer simply wasn't ticking here, because the bees weren't seeing any image motion at all.
KNOY: Well, with all due respect, Professor, this is very interesting. But why do we need to know this?
SRINIVASAN: One of the things we are pursuing is looking to incorporate some of these principles into flying vehicles. You know, if you try to swat a fly, for example, or watch a fly do a graceful landing on the rim of your coffee cup, you notice that it has an exquisitely sensitive visual system and a very precise flight control system. And it does all this with a brain that weighs less than, you know, a tenth of a milligram. So the question is, how do they do this, and do they use any simple tricks that we could learn about and perhaps incorporate into small flying machines that fly about autonomously?
KNOY: It's something that the military has been interested in.
SRINIVASAN: Well, for all kinds of surveillance, for example, it's safer, I suppose, to have vehicles that would be unmanned, and that could be sent away, dispatched on missions to do reconnaissance, surveillance. Having some sort of autonomous vehicle like this that can be told to just simply get there, get somewhere, and have a holding pattern there where it could observe the coastline, or observe something that's going on of interest, would be very useful.
KNOY: Mandyam Srinivasan is a biologist at Australia National University in Canberra. Thanks for joining us.
SRINIVASAN: Thank you very much, Laura.
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