Hot feet and cool heads — reasons for dung beetles to dance | Marcus Byrne |TEDxWitsUniversity

This talk was given at a local TEDx event, produced independently of the TED Conferences.
Marcus Byrne's research interests revolve around the use of insects for biological control. His talk unveils some of the secrets of dung beetles survival and adaptation to their environment.

This is poo.

And what I want to do today
is share my passion for poo with you.

What you might find more fascinating

is the way these small animals
deal with poo.

So this animal here

has a brain about the size
of a grain of rice.

And yet, it can do things

you and I couldn't possibly entertain
the idea of doing.

Basically, it all evolved to handle

its food source which is dung.

So the question is,
"Where do we start this story?"

It seems appropriate to start at the end

because this is a waste product
that comes out of other animals

but it still contains nutrients

and there are
sufficient nutrients in there

for dung beetles to make a living.

So dung beetles eat dung,

and their larvae are also dung feeders;

they are grown completely
in a ball of dung.

Within South Africa we've got
about 800 species of dung beetles,

in Africa we've got
2,000 species of dung beetles,

and in the world we have about
6,000 species of dung beetles.

So, according to dung beetles,
dung is pretty good stuff.

The question is: "How do
they deal with this material?"

And most dung beetles actually
wrap it into a package of some sort.

It's made into a discrete ball,

but most of the time you won't see that

unless you're prepared to get
dung under your fingernails

and rout through the dung itself,

you'll never see 90%
of the dung beetle species

because they go directly into the dung,
straight down below it,

and then they shuttle back and forth

between the dung at the soil's surface
and the nest they make underground.

But fortunately for us,

10% of the species actually make a ball.

They roll away this ball
from the dung source

and usually bury it at a remote place

away from the dung source.

They have a very particular behavior

by which they are able
to roll their balls.

This is the very proud owner
of a beautiful dung ball.

You can see it's a male
— he's got hairy legs there.

He's clearly very pleased
about what he's sitting on there.

But then he's about to become a victim
of a vicious smash and grab.

(Laughter)

This is a clear indication
that this is a valuable resource.

And valuable resources
have to be looked after,

and guarded in a particular way,

and we think the reason they roll
the balls away is because of this:

because of the competition

that is involved
in getting hold of that dung.

This dung pat was actually

— well, it wasn't a dung pat

15 minutes before
this photograph was taken —

we think it's the intense competition
that makes the beetles

so well adapted to rolling balls of dung.

What you've got to imagine here

is this animal moving across
the African veld.

Its head is down, it's walking backwards,

it's the most bizarre way to transport
your food in any particular direction.

And, at the same time,
it has got to deal with the heat.

This is Africa. It's hot.

So what I want to share with you now

are some of the experiments that myself
and my colleagues have used

to investigate how dung beetles
deal with these problems.

So, watch this beetle.

There are two things
I want you to be aware of,

the first is how it deals with
this obstacle we've put in in its way.

See, it does a little dance.

And then it carries on
in exactly the same direction

that it took in the first place.

A little dance,

and then heads off
in a particular direction.

So, clearly, this animal
knows where it's going

and it knows where it wants to go.

And that's a very important thing,

because if you think about it,
you're at the dung pile,

you've got this great big pile

that you want to get away
from everybody else,

and the quickest way
to do it is in a straight line.

So we gave them
some more tasks to deal with.

And what we did here,

is we turned the world under their feet.

And watch its response.

So this animal has actually had
the whole world turned under its feet,

it's turned by 90 degrees,
but it doesn't flinch.

It knows exactly where it wants to go

and it heads off
in that particular direction.

So, our next question then was:

"How are they doing this?
What are they doing?"

And there was a cue
that was available to us;

every now and then,
they climb on top of the ball

and they take a look
at the world around them.

What do you think
they could be looking at

as they climb on top of the ball?

What are the obvious cues
that this animal could use

to direct its movement?

The most obvious one
is to look at the sky.

So, we thought:

"What could they
be looking at in the sky?"

and the obvious thing
to look at is the sun.

A classic experiment here.

We moved the sun.

So what we're going to do
now is shade the sun with a board,

and then move the sun with a mirror
to a completely different position.

And look at what the beetle does.

It does a little double dance.

And then it heads back
in exactly the same direction

it went in the first place.

(Laughter)

It makes up its mind

and heads back
in the opposite direction.

So, clearly they're looking at the sun.

The sun is a very important cue
in the sky for them.

The thing is the sun
is not always available to you,

because at sunset
it disappears below the horizon.

What is happening in the sky here

is that there's a great big pattern

of polarized light in the sky
that you and I can't see.

It's the way our eyes are built.

But the sun is at the horizon over here,

and we know that when the sun
is at the horizon,

— so it's over on this side —

there is a north-south,
huge pathway across the sky

of polarized light that we can't see.

But the beetles can see it.

So, how do we test that?
Well, that's easy.

We get a great big polarization filter,

pop the beetle underneath it,

and the filter is at right angles
to the polarization pattern in the sky.

The beetles comes out
from underneath the filter,

and it does a right hand turn

because it comes back under the sky
that it was originally orientated to,

and then reorientates itself back

to the direction
it was originally going in.

Obviously, beetles
can see polarized light.

So, what we've got so far

is, "What are beetles doing?"
— they're rolling balls —

"How are they doing it?"
— they're rolling them in a straight line—

"How are they maintaining
a particular straight line?"

— they are looking at
celestial cues in the sky,

some of which you and I can't see.

But "How do they pick up
those celestial cues?"

was of interest to us next.

And it was
this particular little behavior,

the dance,

that we thought was important,

because — look!

It takes a pause, every now and then,

and then heads off in the direction
that it wants to go in.

What are they doing
when they do this dance?

How far can we push them
before they will reorientate themselves?

In this experiment here,
we forced them into a channel

and you can see
he wasn't particularly forced

into this particular channel,

and we gradually displaced
the beetle by 180 degrees

until this individual ends up going
in exactly the wrong direction.

It ends up going in exactly
the opposite direction

that it wanted to go to
in the first place.

And let's see what his reaction is,

as he is headed through 90 degrees here,

and when he ends up down here,

he's going to be 180 degrees
in the wrong direction.

And see what its response is.

He does a little dance,

and turns around and heads back.

He knows exactly where he is going,

he knows exactly what the problem is,

and he knows exactly how to deal with it.

And the dance is a transition behavior

that allows them
to reorientate themselves.

So, that's the dance.

But after spending many years
sitting in the African bush,

watching dung beetles on nice hot days,

we noticed that there was another behavior

associated with the dance behavior.

You'll see it in this video here.
It's very obvious.

Every now and then,

when they climb on top of the ball

they wipe their face.

And you see him do it again.

Now what could be going on here?

Clearly the ground is very hot.

When the ground is hot,
they dance more often.

And when they do this particular dance,

they wipe the bottom of their face.

We thought that it could be
a thermoregulatory behavior,

maybe what they're doing
is trying to get off the hot soil

and also spitting on their face
to cool their head down.

So we designed a couple of arenas.

One was hot, one was cold;

we shaded this one, we left that one hot.

We were able to swap them around.

Then, we filmed them
with a thermal camera.

What you're looking at here,

is a heat image of the system.

And what you can see here
emerging from the poo,

is a cool dung ball.

So the truth is,

if you look at the temperature over here,

dung is cool.

(Laughter)

All we're interested in here is comparing

the temperature of the beetle
against the background.

The background here is about 50°C.

The beetle itself and the ball

are probably around 30°C to 35°C.

This is a great big ball of icecream

that this beetle is now transporting

across the hot veld.

It isn't climbing, it isn't dancing

because its body temperature
is actually relatively low,

it's about the same as yours and mine.

What's of interest here,

is that its little brain is quite cool.

But if we contrast now
what happens in a hot environment,

— and look at this particular beetle,

look at the temperature of the soil —

it's up around 55°C to 60°C.

Watch how often the beetle dances.

Look at its front legs.
They're roaringly hot.

The ball leaves a little thermal shadow,

and the beetle climbs on top
of the ball and wipes its face,

and all the time it's trying
to cool itself down, we think,

and avoid the hot sand
that it's walking across.

That was pretty interesting.

We were interested
in the temperature of the legs,

and what we did then was
put little boots on these legs,

because this was a way to test
if the legs were involved

in sensing the temperature of the soil.

If you look over here,

with boots, they climb
onto the ball far less often

than when they had no boots on.

We described these as cool boots.

It was a dental compound
that we used to make them.

We also cooled down the dung ball,

so we were able to put
the ball in the fridge,

gave them a nice cool dung ball,

and they climbed onto that ball

far less often than when
they had a hot ball.

This is called stilting.

It's a thermal behavior that you
and I do when we cross the beach,

we jump onto a towel,
or somebody else's towel,

"Sorry! I jumped onto your towel!"

then you scuttle across
on somebody else's towel

and that way you don't burn your feet.

And that's exactly what
the beetles are doing here.

However, there's one more story
I'd like to share with you

and that's this particular species.

It's from a genus called pachysoma,

there are 13 species in the genus.

They have a particular behavior
that you will find interesting.

This is a dung beetle.
Watch what he's doing.

Can you spot the difference?

They don't normally go this slowly.

This is in slow motion.

But it's walking forward
and it's dragging a pellet with it,

it's taking a pellet
of dried dung with it.

This is a different species
in the same genus,

but it has exactly
the same foraging behavior.

So what's going on here?

One more interesting aspect

of this dung beetle's behavior
that we found quite fascinating,

and that's it forages
and provisions a nest.

Watch this individual here.

What he's trying to do is set up a nest.

He doesn't like his first position,

but he comes up with a second position,

and about 50 minutes later,
that nest is finished

and he heads off
to forage and provision

at a pile of dried dung pellets.

Notice the outward path,
compared to the homeward path.

And compare the two.

By and large, you'll see
that the homeward path

is far more direct
than the outward path.

On the outward path,
he's always on the lookout

for a new blob of dung.

On the way home,

— he knows where home is —
and he wants to go straight there.

The important thing here,
is that this isn't a one way trip.

As with most dung beetles,
the trip here,

is repeated back and forth

between the provisioning site
and the nest site.

Watch, you're going to see
another South African crime

taking place right now!

(Laughter)

His neighbor steals
one of his dung pellets.

This is a behavior called
"path integration."

The beetle has a home spot,

it goes out on a convoluted path,
looking for food;

when it finds food,
it heads straight home,

it knows exactly where its home is.

Now there are two ways
it could be doing that.

We can test what it's doing
by displacing the beetle

to a new position when
it's at the foraging site.

If it's using landmarks,
it will find its home.

If it's using "path integration,"
it won't find its home,

it will arrive at the wrong spot.

Here it's using path integration.

It's counting its steps,

measuring the distance
out in this direction,

it knows the bearing home,

it knows it should be in that direction.

If you displace it,
it ends up in the wrong place.

Let's see what happens

when we put this beetle to the test

with a similar experiment.

Here's our cunning experimenter.

He displaces the beetle,

and now we have to see
what is going to take place.

He doesn't like
that piece. He rejects it.

He climbs onto the paper
and is moved to a new position.

Now, what we've got is a burrow.

That's where the forage was.

The forager has been displaced
to a new position.

If he's using landmark orientation

he should be able to find the burrow

because he should be able to recognize

the landmarks around it.

If he's using path integration

then it should end up in the wrong spot.

Over here.

So let's watch what happens

when we put the beetle
through the whole test.

So there it is there.

He's about to head home,

and look what happens.

Shame.

It hasn't a clue.

It starts to search for its house,

in the right distance away from the food

but it's clearly completely lost.

So we know now that this animal

uses path integration
to find its way around.

And the callous experimenter
leaves at top left.

So what we're looking at here

are a group of animals
that use a compass,

they use the sun as a compass
to find their way around.

They have some sort of system
for measuring that distance.

We know that these species
here count their steps.

That's what they use as an odometer,

a step counting system

to find their way back home.

We don't know yet what dung beetles use.

What have we learned from these animals

with a brain the size of a grain of rice?

Well, we know they can
roll balls in a straight line

using celestial cues.

We know that the dance behavior
is an orientation behaviour,

and it's also
a thermoregulation behavior,

and we also know that they use
a path integration system

for finding their way home.

So, for a small animal,

dealing with a fairly revolting substance,

we can actually learn
an awful lot from these behaviors,

doing things that you
and I couldn't possibly do.

Thank you.

(Applause)