17:09
TEDxWitsUniversity

Marcus Byrne: The dance of the dung beetle

Filmed:

A dung beetle has a brain the size of a grain of rice, and yet shows a tremendous amount of intelligence when it comes to rolling its food source -- animal excrement -- home. How? It all comes down to a dance. (Filmed at TEDxWitsUniversity.)

- Entomologist
Marcus Byrne is fascinated by the way insects, particularly the intrepid dung beetle, have hardwired solutions to the challenges posed by their environments. Could they help humans solve problems? Full bio

This is poo,
00:16
and what I want to do today is share my passion
00:18
for poo with you,
00:21
which might be quite difficult,
00:24
but I think what you might find more fascinating
00:27
is the way these small animals deal with poo.
00:30
So this animal here has got a brain
00:33
about the size of a grain of rice, and yet it can do things
00:35
that you and I couldn't possibly entertain the idea of doing.
00:39
And basically it's all evolved to handle its food source,
00:43
which is dung.
00:47
So the question is, where do we start this story?
00:49
And it seems appropriate to start at the end,
00:52
because this is a waste product that comes out
00:55
of other animals, but it still contains nutrients
00:58
and there are sufficient nutrients in there
01:01
for dung beetles basically to make a living,
01:03
and so dung beetles eat dung, and their larvae
01:06
are also dung-feeders.
01:09
They are grown completely in a ball of dung.
01:11
Within South Africa, we've got about 800 species of dung beetles,
01:15
in Africa we've got 2,000 species of dung beetles,
01:18
and in the world we have about 6,000 species of dung beetles.
01:22
So, according to dung beetles, dung is pretty good.
01:26
Unless you're prepared to get dung under your fingernails
01:31
and root through the dung itself, you'll never see
01:34
90 percent of the dung beetle species,
01:37
because they go directly into the dung,
01:39
straight down below it, and then they shuttle back and forth
01:42
between the dung at the soil surface
01:44
and a nest they make underground.
01:46
So the question is, how do they deal with this material?
01:49
And most dung beetles actually wrap it into a package of some sort.
01:54
Ten percent of the species actually make a ball,
01:58
and this ball they roll away from the dung source,
02:02
usually bury it at a remote place away from the dung source,
02:06
and they have a very particular behavior
02:10
by which they are able to roll their balls.
02:13
So this is a very proud owner of a beautiful dung ball.
02:18
You can see it's a male
02:22
because he's got a little hair on the back of his legs there,
02:23
and he's clearly very pleased about what he's sitting on there.
02:25
And then he's about to become a victim
02:30
of a vicious smash-and-grab. (Laughter)
02:32
And this is a clear indication
02:37
that this is a valuable resource.
02:40
And so valuable resources have to be looked after
02:43
and guarded in a particular way, and we think
02:47
the reason they roll the balls away is because of this,
02:50
because of the competition that is involved
02:53
in getting hold of that dung.
02:56
So this dung pat was actually -- well, it was a dung pat
02:58
15 minutes before this photograph was taken,
03:01
and we think it's the intense competition
03:03
that makes the beetles so well-adapted
03:06
to rolling balls of dung.
03:10
So what you've got to imagine here is this animal here
03:13
moving across the African veld.
03:15
Its head is down. It's walking backwards.
03:18
It's the most bizarre way to actually transport your food in any particular direction,
03:22
and at the same time it's got to deal with the heat.
03:27
This is Africa. It's hot.
03:30
So what I want to share with you now
03:32
are some of the experiments that myself and my colleagues
03:34
have used to investigate how dung beetles
03:37
deal with these problems.
03:42
So watch this beetle,
03:44
and there's two things that I would like you to be aware of.
03:46
The first is how it deals with this obstacle
03:51
that we've put in its way. See, look, it does a little dance,
03:53
and then it carries on in exactly the same direction
03:56
that it took in the first place.
03:59
A little dance, and then heads off in a particular direction.
04:03
So clearly this animal knows where it's going
04:06
and it knows where it wants to go,
04:10
and that's a very, very important thing,
04:11
because if you think about it, you're at the dung pile,
04:13
you've got this great big pie that you want to get away from everybody else,
04:15
and the quickest way to do it is in a straight line.
04:20
So we gave them some more tasks to deal with,
04:23
and what we did here is we turned the world
04:27
under their feet. And watch its response.
04:31
So this animal has actually had the whole world
04:41
turned under its feet. It's turned by 90 degrees.
04:43
But it doesn't flinch. It knows exactly where it wants to go,
04:46
and it heads off in that particular direction.
04:49
So our next question then was,
04:52
how are they doing this?
04:54
What are they doing? And there was a cue that was available to us.
04:56
It was that every now and then they'd climb on top of the ball
04:59
and they'd take a look at the world around them.
05:02
And what do you think they could be looking at
05:05
as they climb on top of the ball?
05:07
What are the obvious cues that this animal could use
05:09
to direct its movement? And the most obvious one
05:12
is to look at the sky, and so we thought,
05:16
now what could they be looking at in the sky?
05:20
And the obvious thing to look at is the sun.
05:23
So a classic experiment here,
05:27
in that what we did was we moved the sun.
05:30
What we're going to do now is shade the sun with a board
05:33
and then move the sun with a mirror
05:36
to a completely different position.
05:38
And look at what the beetle does.
05:40
It does a little double dance,
05:42
and then it heads back in exactly the same direction
05:45
it went in the first place.
05:47
What happens now? So clearly they're looking at the sun.
05:49
The sun is a very important cue in the sky for them.
05:53
The thing is the sun is not always available to you,
05:56
because at sunset it disappears below the horizon.
05:59
What is happening in the sky here
06:03
is that there's a great big pattern of polarized light in the sky
06:06
that you and I can't see. It's the way our eyes are built.
06:10
But the sun is at the horizon over here
06:13
and we know that when the sun is at the horizon,
06:17
say it's over on this side,
06:20
there is a north-south, a huge pathway across the sky
06:22
of polarized light that we can't see
06:26
that the beetles can see.
06:29
So how do we test that? Well, that's easy.
06:31
What we do is we get a great big polarization filter,
06:34
pop the beetle underneath it, and the filter is at right angles
06:37
to the polarization pattern of the sky.
06:42
The beetle comes out from underneath the filter
06:44
and it does a right-hand turn,
06:48
because it comes back under the sky
06:51
that it was originally orientated to
06:53
and then reorientates itself back
06:56
to the direction it was originally going in.
06:58
So obviously beetles can see polarized light.
07:02
Okay, so what we've got so far is,
07:08
what are beetles doing? They're rolling balls.
07:11
How are they doing it? Well, they're rolling them in a straight line.
07:14
How are they maintaining it in a particular straight line?
07:17
Well, they're looking at celestial cues in the sky,
07:20
some of which you and I can't see.
07:23
But how do they pick up those celestial cues?
07:25
That was what was of interest to us next.
07:27
And it was this particular little behavior, the dance,
07:30
that we thought was important, because look,
07:33
it takes a pause every now and then,
07:36
and then heads off in the direction that it wants to go in.
07:38
So what are they doing when they do this dance?
07:42
How far can we push them before they will reorientate themselves?
07:46
And in this experiment here, what we did was we forced them
07:51
into a channel, and you can see he wasn't
07:54
particularly forced into this particular channel,
07:57
and we gradually displaced the beetle by 180 degrees
08:00
until this individual ends up going in exactly the opposite direction
08:05
that it wanted to go in, in the first place.
08:09
And let's see what his reaction is
08:11
as he's headed through 90 degrees here,
08:14
and now he's going to -- when he ends up down here,
08:17
he's going to be 180 degrees in the wrong direction.
08:19
And see what his response is.
08:22
He does a little dance, he turns around,
08:24
and heads back in this. He knows exactly where he's going.
08:27
He knows exactly what the problem is,
08:31
and he knows exactly how to deal with it,
08:33
and the dance is this transition behavior
08:35
that allows them to reorientate themselves.
08:37
So that's the dance, but after spending many years
08:40
sitting in the African bush watching dung beetles on nice hot days,
08:45
we noticed that there was another behavior
08:49
associated with the dance behavior.
08:51
Every now and then, when they climb on top of the ball,
08:54
they wipe their face.
08:57
And you see him do it again.
09:01
Now we thought, now what could be going on here?
09:04
Clearly the ground is very hot, and when the ground is hot,
09:07
they dance more often, and when they do this particular dance,
09:10
they wipe the bottom of their face.
09:12
And we thought that it could be a thermoregulatory behavior.
09:14
We thought that maybe what they're doing is trying to
09:17
get off the hot soil and also spitting onto their face
09:19
to cool their head down.
09:23
So what we did was design a couple of arenas.
09:25
one was hot, one was cold.
09:29
We shaded this one. We left that one hot.
09:32
And then what we did was we filmed them with a thermal camera.
09:34
So what you're looking at here is a heat image
09:37
of the system, and what you can see here emerging
09:42
from the poo is a cool dung ball.
09:46
So the truth is, if you look at the temperature over here,
09:49
dung is cool. (Laughter)
09:53
So all we're interested in here is comparing the temperature
09:58
of the beetle against the background.
10:01
So the background here is around about 50 degrees centigrade.
10:03
The beetle itself and the ball are probably around about
10:07
30 to 35 degrees centigrade,
10:10
so this is a great big ball of ice cream
10:12
that this beetle is now transporting across the hot veld.
10:15
It isn't climbing. It isn't dancing, because
10:18
its body temperature is actually relatively low.
10:21
It's about the same as yours and mine.
10:23
And what's of interest here is that little brain is quite cool.
10:27
But if we contrast now what happens in a hot environment,
10:31
look at the temperature of the soil.
10:36
It's up around 55 to 60 degrees centigrade.
10:38
Watch how often the beetle dances.
10:41
And look at its front legs. They're roaringly hot.
10:45
So the ball leaves a little thermal shadow,
10:49
and the beetle climbs on top of the ball
10:52
and wipes its face, and all the time it's trying to cool itself down,
10:54
we think, and avoid the hot sand that it's walking across.
10:59
And what we did then was put little boots on these legs,
11:05
because this was a way to test if the legs
11:08
were involved in sensing the temperature of the soil.
11:11
And if you look over here, with boots they climb onto the ball
11:15
far less often when they had no boots on.
11:19
So we described these as cool boots.
11:23
It was a dental compound that we used to make these boots.
11:26
And we also cooled down the dung ball, so we were able
11:29
to put the ball in the fridge, gave them a nice cool dung ball,
11:31
and they climbed onto that ball far less often
11:35
than when they had a hot ball.
11:38
So this is called stilting. It's a thermal behavior
11:39
that you and I do if we cross the beach,
11:42
we jump onto a towel, somebody has this towel --
11:44
"Sorry, I've jumped onto your towel." --
11:47
and then you scuttle across onto somebody else's towel,
11:48
and that way you don't burn your feet.
11:51
And that's exactly what the beetles are doing here.
11:53
However, there's one more story I'd like to share with you,
11:56
and that's this particular species.
11:59
It's from a genus called Pachysoma.
12:00
There are 13 species in the genus, and they have
12:03
a particular behavior that I think you will find interesting.
12:06
This is a dung beetle. Watch what he's doing.
12:12
Can you spot the difference?
12:17
They don't normally go this slowly. It's in slow motion.
12:20
but it's walking forwards,
12:23
and it's actually taking a pellet of dry dung with it.
12:25
This is a different species in the same genus
12:28
but exactly the same foraging behavior.
12:31
There's one more interesting aspect of this
12:35
dung beetle's behavior that we found quite fascinating,
12:37
and that's that it forages and provisions a nest.
12:42
So watch this individual here, and what he's trying to do
12:46
is set up a nest.
12:49
And he doesn't like this first position,
12:52
but he comes up with a second position,
12:53
and about 50 minutes later, that nest is finished,
12:55
and he heads off to forage and provision
12:59
at a pile of dry dung pellets.
13:03
And what I want you to notice is the outward path
13:05
compared to the homeward path, and compare the two.
13:08
And by and large, you'll see that the homeward path
13:13
is far more direct than the outward path.
13:15
On the outward path, he's always on the lookout
13:18
for a new blob of dung.
13:21
On the way home, he knows where home is,
13:23
and he wants to go straight to it.
13:25
The important thing here is that this is not a one-way trip,
13:28
as in most dung beetles. The trip here is repeated
13:32
back and forth between a provisioning site and a nest site.
13:35
And watch, you're going to see
13:39
another South African crime taking place right now. (Laughter)
13:40
And his neighbor steals one of his dung pellets.
13:44
So what we're looking at here
13:49
is a behavior called path integration.
13:52
And what's taking place is that the beetle
13:56
has got a home spot, it goes out on a convoluted path
13:58
looking for food, and then when it finds food,
14:02
it heads straight home. It knows exactly where its home is.
14:06
Now there's two ways it could be doing that,
14:10
and we can test that by displacing the beetle
14:13
to a new position when it's at the foraging site.
14:16
If it's using landmarks, it will find its home.
14:19
If it is using something called path integration,
14:22
it will not find its home. It will arrive at the wrong spot,
14:25
and what it's doing here if it's using path integration
14:29
is it's counting its steps or measuring the distance out in this direction.
14:31
It knows the bearing home, and it knows it should be in that direction.
14:35
If you displace it, it ends up in the wrong place.
14:39
So let's see what happens when we put this beetle
14:42
to the test with a similar experiment.
14:45
So here's our cunning experimenter.
14:48
He displaces the beetle,
14:52
and now we have to see what is going to take place.
14:55
What we've got is a burrow. That's where the forage was.
15:00
The forage has been displaced to a new position.
15:03
If he's using landmark orientation,
15:06
he should be able to find the burrow,
15:08
because he'll be able to recognize the landmarks around it.
15:10
If he's using path integration,
15:13
then it should end up in the wrong spot over here.
15:16
So let's watch what happens
15:19
when we put the beetle through the whole test.
15:22
So there he is there.
15:25
He's about to head home, and look what happens.
15:27
Shame.
15:33
It hasn't a clue.
15:36
It starts to search for its house in the right distance
15:38
away from the food, but it is clearly completely lost.
15:41
So we know now that this animal uses path integration
15:47
to find its way around, and the callous experimenter
15:51
leads it top left and leaves it. (Laughter)
15:55
So what we're looking at here are a group of animals
15:58
that use a compass, and they use the sun as a compass
16:02
to find their way around,
16:04
and they have some sort of system
16:06
for measuring that distance,
16:09
and we know that these species here actually
16:10
count the steps. That's what they use as an odometer,
16:14
a step-counting system, to find their way back home.
16:16
We don't know yet what dung beetles use.
16:22
So what have we learned from these animals
16:24
with a brain that's the size of a grain of rice?
16:27
Well, we know that they can roll balls in a straight line
16:30
using celestial cues.
16:34
We know that the dance behavior is an orientation behavior
16:36
and it's also a thermoregulation behavior,
16:39
and we also know that they use a path integration system
16:42
for finding their way home.
16:46
So for a small animal dealing with a fairly revolting substance
16:48
we can actually learn an awful lot from these things
16:52
doing behaviors that you and I couldn't possibly do.
16:55
Thank you. (Applause)
16:58
Translated by Joseph Geni
Reviewed by Morton Bast

▲Back to top

About the Speaker:

Marcus Byrne - Entomologist
Marcus Byrne is fascinated by the way insects, particularly the intrepid dung beetle, have hardwired solutions to the challenges posed by their environments. Could they help humans solve problems?

Why you should listen

Marcus Byrne is professor of zoology and entomology at Wits University in Johannesburg, South Africa. His research explores what humans can learn from insects. One of the big questions he's focused on: how can we control alien weeds, which threaten biodiversity? Byrne believes that insects may hold the 'magic bullet' for how to restrain the growth of these plants, which jockey for resources with native flora and fauna.

Byrne's work has also focused on the unique mechnics of the dung beetle. His research has shown that the dung beetle has a highly effective visual navigation system, that allows them to roll balls of animal dung with precision back to their home, even in the dark of night and the hottest of conditions. Byrne wonders: can this beetle teach humans how to solve complex visual problems?

 

More profile about the speaker
Marcus Byrne | Speaker | TED.com