Bees: Nature's mathematicians

16 May 2017

Interview with 

Srini Srinivasan, University of Queensland

BEE-FLYING-TO-THISTLE

A honeybee hovering above a thistle

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Bees are able to build those fantastic hexagonal honeycombs but, apparently, they’re also able to count! But do they deserve their reputation as nature's mathematicians? Georgia Mills spoke to Srini Srinivasan from the University of Queensland to find out how they discovered counting bees...

Srini - We trained them to fly down a tunnel - a small corridor - that carried a reward of sugar water at the far end, and we had a series of identical landmarks that they flew past along the way. Only one of the landmarks carried a food reward (sugar solution) and they had to, by flying through and testing out the various landmarks, they had to work out which particular landmark carried a flood reward. Whether it was the second one, the third one, or the fourth one, or fifth one, and so on. We did find, for example, with some training they could tell which particular landmark carried the food reward.

Georgia - I’m assuming these landmarks were identical apart from the number of them the bees had flown past?

Srini - Exactly. Then you’ve also go to make sure they’re not cheating and using another cue that they potentially could also use as honey bees. They have a visually driven odometer that tells them how far they have flown by measuring how much the image of the world has moved past their eyes. So they could be using that as a cue, they could be measuring distance to the correct landmark rather than counting these landmarks, right? So the way to control for that is to randomly vary the separation between the various landmarks to make sure they realise that distance is not a useful cue and they really have to learn how to count. So that’s what we did.

Georgia - How high can bees count?

Srini - Well, it looks like they can manage up to four in the sequential counting task-  not much more than that.

Georgia - Only four!

Srini - But surprisingly, that number four seems to be a fairly universal number. Many animals, and also among children for example, we can only count up to four or five when a number of objects briefly are presented to us on a screen in a very temporary way. It’s called subitizing I believe - that’s the name for it. And it’s a form of primitive counting that we indulge in or we have to cope with when we have limited processing time. Animals seem to have that and so do infants. So it’s a basic counting module that all living creatures seem to have, more or less.

Georgia - Why is it useful for bees to be able to count to four?

Srini - If there are prominent landmarks along the way it does make sense, I suppose, to keep track of them as well as the distance travelled so that could aid you in locating and pinpointing your source. Also, if a bee needs to decide whether it’s worthwhile landing on a flower or not. If there’s a large number of bees already there it’s probably not worthwhile for it to actually get down there and jostle amongst these various bees and spend time and energy trying to get to the food source, it might as well try a different flower. So it does help for bees to have a rough idea of how many bees there are on a particular site.

Georgia - And they just don’t need to really count above this number then?

Srini - It seems like anything beyond four translates to many, and they cannot really distinguish between four and five, and five and six, and so on.

Georgia - One, two, three, four, many! It would have made maths classes a lot easier. Are bees particularly good at maths then? Are there other animals that can count too?

Srini - It’s been looked at in fish, in birds, in chimpanzees, and so on and this magic number of between five and six seems to crop up in almost all the species, so it’s quite interesting. Birds, for example, probably need to know how many eggs there are in the nest and if one of them has fallen off or been taken away by another bird. So that’s probably useful for them to be able to keep track of how many eggs there are.

Quite often counting the number of animals in a pack is probably helpful if you’re a wolf or something and you decide whether you want to go to a fight with that pack or not. So that counting ability seems to there for a lot of animals, not just bees and I wouldn’t claim that bees are the best counters in the world. No, I wouldn’t say that.

Georgia - Is that right reserved for humans? It’s really cool bees can count, especially as they’ve got very, very small brains. But why are you studying this?

Srini - It was by accident! This is not the main focus of our research I should admit - this is just a one-off thing we did. We were using this tunnel paradigm to study a whole bunch of other things that bees do. For example, the fact that bees measure, they’re excellent navigators, and they measure how far they’ve flown. Not by measuring time of flight, or the energy consumed, or counting the number of wingbeats that it takes to get to their food source, they actually do it visually by measuring how much the image of the world has moved in their eyes. That’s something we were able to do using this tunnel paradigm by making bees fly down this tunnel and looking to see how they danced when the came back. Because the dance conveys information to the other bees about how far away the food source is.

Georgia - Ah yes. This is the famous “waggle dance,” isn’t it?

Srini - The waggle dance - exactly right. So when they fly in this narrow tunnel, even when they fly a short distance, they could comprehensively be fooled. They think they’ve flown a long distance because they experience a large amount of image motion on the way to the food because the walls are very close to the eyes, as is the floor, so even a small amount of forward movement makes you think you’ve flown a long distance.

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