to within a fraction of a millimetre.
Their eyes are at the end of stalks that stick out sideways from their heads.
They threaten with their forelegs.
But the crucial factor that decides whether they will fight
is the distance apart of their eyes.
Rival males square up head to head.
A bigger eyespan indicates a bigger body and, therefore, greater strength.
If a fly discovers that it's outgunned, it will back away.
These, however, have established that they are equally matched.
Now there will have to be a joust to get a settlement.
Size of claw is the criterion used to settle disputes between these little mud crabs.
They quarrel over the ownership of a burrow.
And when one is convinced that its rival is bigger, then that's that.
The biggest weapons of all are developed by males
who battle not over burrows, nor over food, but directly over females,
as these bull elephants are doing.
If success in such battles brings the ability to mate with many females
to the exclusion of all other males who are less well-armed,
then male weapons, over many generations, will become enormous,
and the battles in which they are used violent in the extreme.
Exactly the same process that turned elephants' teeth into tusks
has created the armaments of the stag beetle.
Their mandibles are so large that they can no longer be used for feeding,
only for fighting.
Beetle fighting technique doesn't just involve charging or pushing.
Instead, each tries to prise his opponent from his footholds and hurl him aside.
Australian antler flies have grappling irons on their heads.
The rules of their contests
are that the one who make the other fall backwards is the winner.
A male ibex is on watch in the deserts of the Middle East.
It's the beginning of the breeding season.
Groups of females are scouring the mountainside,
searching for a few leaves to eat.
The males, however, are seeking out one another.
Who is going to rule in these mountains?
First, a cautious assessment.
This, impressive though it seems,
is still merely a measurement of each other's strength.
If one is a little less strong,
there's still time for discretion to be the better part of valour.
But if both decide they have a chance of winning, then battle begins.
This is a dangerous country in which to fight.
Sometimes a losing animal is killed by being forced over a cliff.
A contestant may be so badly injured, he never recovers.
But when the arms race between males
has equipped rivals with weapons of this size,
that is the price that may have to be paid for the perpetuation of your genes.
Gazelles also have formidable armaments.
A stab from their horns could be lethal.
Yet the mood among the bucks is very different from among the ibex.
Actual battles are relatively rare.
Rival Grant's gazelles assess one another's strengths with such care and reserve
that a casual eye might not even recognise that this graceful gavotte
has anything to do with conflict.
They turn...
...and nod.
They resume their parallel walk.
This elegant ritualised parade is enough to convince
most of the bucks in most of their disputes which of them is the victor.
No conflict could be more restrained.
But even among those animals who roar and snarl and brandish their weapons,
most confrontations are settled with a similar lack of violence.
Risking injury is the final resort.
Restraint generally pays.
Eagles lead lonely lives.
This one, flying over the gaunt mountains of northern Scotland,
may spend days without seeing another of its own kind.
In spring, when a pair are raising one or, at the most, two chicks,
young rabbits and birds are not difficult to find.
But now, late in the year, food is scarce,
and there's barely enough on this bleak hillside to support a pair.
The chicks had to leave to find hillsides of their own.
So an eagle doesn't have to deal with the problems that face
and can even dominate the lives of more sociable animals.
Unlike the lonely eagle, many animals live in groups.
But that inevitably causes problems.
How do you get on with your friends and,
more particularly, your rivals, without continual squabbles?
There's another big bird in these Scottish skies,
bigger even than the golden eagle.
It comes here in the autumn and then it forms large flocks.
Hooper swans, coming in to land after a 1,000-mile journey from Iceland.
There the winter will be dark and bitterly cold.
The birds have flown down to spend the winter here
in the milder conditions of Scotland.
Suitable stretches of water,
secluded with plenty of vegetation around to eat, are few,
and this loch will soon be crowded.
Some of the arrivals are young birds travelling by themselves
who've yet to find a mate.
The next few months will be their opportunity
to form partnerships that will last a lifetime.
Most are families, pairs with their six-month-old cygnets hatched in Iceland.
They will stay together until the next spring.
They proclaim their arrival with a clear challenge to those already here.
They, too, intend to claim a place on the lake.
The male fights most of the necessary battles.
But his mate always backs him up,
and the pair celebrates a successful skirmish
with an ecstatic triumph ceremony.
There's a clear pattern to these encounters.
Pairs consistently win against singletons.
But the most dominant of all are the families: mother, father and cygnets.
This is a particularly powerful one. It has four young.
Singletons, or even pairs, who come too close are quickly seen off.
The cygnets enthusiastically join in the triumph ceremonies.
As long as they stay close to their parents,
they will be treated with respect by other birds.
But if they stray, they will be shown no mercy.
In the meantime, other members of the flock come to recognise and respect
the most powerful families and avoid confrontations where they can.
An apparent peace breaks out on the lake.
But not all seniorities are settled in such a straightforward way,
particularly within groups.
Chickens, when allowed to range freely in a farmyard, as these are,
form themselves into small, tightly-organised
and remarkably stable groups.
Usually there's a cockerel and then a number of hens around him,
and maybe one or two other cockerels on the sidelines.
One of the first studies ever made
to find out how animals organise themselves in groups
was done with a group of chickens like this.
If there are ten or less in the group, then every bird knows every other individually.
They move around in a flock, scratching around for whatever they can get,
apparently harmoniously.
But if I give them something they really like,
then they reveal their true competitive nature.
Watch this.
This pale hen is particularly aggressive.
If she doesn't get to the food first,
she'll peck those who do so until they give way to her.
This dark hen behaves in the same way
and pecks everyone except the fierce pale hen, whom she avoids.
The result of these skirmishes is a peck order,
a line of seniority in which each bird knows its place.
Should the lowliest hen, at the bottom of the peck order,
find a coveted morsel first,
she'll be chased and harried by all the others until she gives it up.
All hens are not equal.
Dominant ones hand out the punishment, junior ones get henpecked.
But for most of the time, the relationships between them seem very friendly,
and life is quiet and productive.
Lions, too, live in groups.
The lionesses form the core of the pride. There may be a dozen or so,
all closely related, mothers and daughters, sisters and aunts.
And it's the lionesses that do most of the hunting.
The two or three males, often brothers, fought as a team
to drive off their predecessors and join the pride.
They'll fight again if newcomers try to displace them.
But most of the time, they have a peaceful life.
Living in groups, for the lions, brings several advantages.
For one thing, they can tackle large, powerful prey, such as buffalo.
These huge animals are three times the weight of a lion.
A single hunter would be very unlikely to tackle a healthy adult buffalo.
It simply wouldn't have the weight and strength to bring one down.
And it might well get injured in the attempt.
But a pride, working together, has a chance.
Despite the numbers pinning it down, the buffalo is still dangerous.
It's finally killed and the feasting begins.
What about seniority and rank in this group?
There's little squabbling or fighting.
This kill has produced such a huge quantity of meat
that there's more than enough for everyone.
So those who haven't got a place at the carcass amiably await their turn.
That's just as well.
Such lethally-armed hunters as these brothers and sisters
could easily kill one another if a dispute became violent.
Only in very hard times, when the pride is extremely hungry,
will issues of priority be settled by fighting.
Lions, cooperating in prides,
dominate the harsh and ruthless world of the African plains.
And the secret of that success is their cooperation.
Working together, no others can match them.
This cooperation extends into other parts of their lives as well.
The lionesses nurture their cubs as a team,
taking turns to guard them and even, on occasion, suckling one another's infants.
Baboons live in even bigger groups, up to 150 or so.
This gives their young, who are defenceless for several years,
the protection that comes from such numbers.
This troop in Kenya is waking up,
having spent the night in the relative safety of its regular sleeping cliff.
Within a baboon troop, there's a fine balance between friendship and rivalry.
Like lions, their societies consist largely of closely-related mothers and their young.
And it's the adult females who largely control affairs.
The powerful males are all outsiders,
who only gained acceptance to the troop by making friends with one or more females.
Grooming is one way that they established such bonds.
Taking charge of a female's baby is another.
A ferocious male can treat an infant with great tenderness,
which is the more remarkable when you consider he may not even be the father.
In baboon society, a social favour like this will be remembered by the mother,
and may improve the male's friendship with her
and the likelihood of him fathering her next baby.
Males consolidate such relationships by encouraging females
to join them for a careful grooming.
Encounters with rival males, however, must be handled carefully.
Lip smacking here is a gesture of appeasement.
Males pull other faces to act as clear come-on signals to passing females.
Meetings can serve several functions.
Seniorities and friendships are reaffirmed.
Babies begin to learn the complex language of smells, gestures,
and the importance of social relationships.
By caring for an infant, a male demonstrates his commitment to its mother.
And the babies, playing together,
learn about making friends, as they must
if they're to achieve a good social position later in life.
In this complex society, social tensions can easily lead to conflict.
When a female is threatened by one male,
she'll seek out another who is a regular ally and cling to him for support.
With a friend's help, she's now safe.
And between them, some hard staring is enough to see off the aggressor.
For baboons, it's not how big you are, but who you know, that counts.
Arguments and squabbles between adult animals
striving to maintain their position within their community are common enough.
But acts of assistance, in which one animal goes to the aid of another
that's got itself into difficulties, these are much rarer.
But this sort of behaviour does seem to occur regularly in one species of animal,
a colony of which is living in this hollow tree.
These bats, all females, habitually roost as a group.
If they go elsewhere, they'll stick together and hang in the same arrangement.
Most are related, although by no means all.
But every bat knows her regular companions well.
At night, they fly off to look for blood.
A donkey is a favourite target.
One lands on its shoulder and shaves a slice of skin
without the donkey noticing.
Another goes for its ear.
The bat's saliva contains an ingredient that prevents blood from clotting,
and it flows freely from the wound.
A third bat tries a different point of attack.
But no, she won't feed tonight.
On returning to the roost, she hangs up beside an old friend.
She turns to her neighbour and licks her face repeatedly, begging for food.
If she goes hungry for more than a day or two, she will die.
But her friend regurgitates enough life-giving blood
to keep her going until the following day.
On another night, the situation may be reversed,
and the bat that's receiving now will repay the gift if it's needed.
But cheats that refuse to give to a neighbour who once helped them
will quickly be detected and, in consequence, may never be helped again.
So, for a vampire, it pays to help your neighbours, whether they're related or not.
Look after them and they will look after you.
Such mutual assistance is much more common
among communities whose members are closely related.
Dwarf mongooses live in groups of a dozen or so
in the tunnels of old overgrown termite hills.
And most of them are the children of one breeding pair.
This is the old female. While she's alive, no other female here will breed.
And this is her mate, the old male.
They feed almost entirely on insects, which they scratch out of the ground
and from rotten logs.
Every day the troop goes to collect them. It's a very time-consuming business.
A nice, big, crunchy beetle.
But digging like this is perilous.
With your head in a hole, you can't see an enemy approaching,
and with your rump in the air, you're dangerously exposed.
So while some hunt, other members of the colony are on guard duty.
These sentinels, usually males, but sometimes females,
will get their turn to feed in due course.
The youngest babies are now coming out.
Their mother can't always be there. She has to spend much of her time feeding.
Junior members of the colony take turns to babysit.
One or two of these babysitters may replace the old breeders one day,
but, for now, the best they can do is serve the colony.
In doing so, they may promote their own genetic line,
for the nurses are often the babies' older sisters,
who carry as many of their genes as their own young would.
A martial eagle, a most dangerous enemy.
The sentinels watch to see if it's coming their way.
If it does, they'll whistle an alarm.
The nurses groom their charges, play with them and catch insects for them.
Though they've never been pregnant, they may even come into milk and suckle them.
By the middle of the day, it's very hot and many of the group need a snooze.
It's safe for them to drop off
because some members of the family are still on guard.
So, by taking turns to help, and waiting for a chance to breed,
the mongooses are able to survive and continue their family line
where, as pairs, they would surely fail.
One mammal has taken this specialisation within the community to an extreme.
Just how extreme hasn't been appreciated until quite recently.
That's hardly surprising, because the most anyone normally sees
of this amazing creature is no more than this.
It's a powerful and industrious digger that spends its entire life underground.
A naked mole rat.
These creatures live in highly inbred groups of 80 or more,
and feed on the gigantic underground tubers developed by some desert plants
for storing food and water.
But they have no way of knowing where these tubers are.
All they can do is dig away and hope they'll eventually bump into one.
So the colony is perpetually tunnelling.
Digging in this hard ground requires teamwork.
Some workers, at the front end of the tunnel, gnaw into the baked earth.
A mole rat's lips close behind the long, curved front teeth,
so that it doesn't get any of the earth into its mouth.
Other team members, behind, kick the soil back along the tunnel
until it reaches one of the surface exits.
It's so unvaryingly hot here that the mole rats need no fur.
Because they're hardly ever in the light, eyes are of little use,
and they're virtually blind, so they run backwards and forwards like tube trains.
Not all the mole rats dig.
A few, a little bigger than the tunnellers, spend most of their time lazing about
in a large central chamber.
These are soldiers.
Some are male, some female. And they're saving their energies for an emergency.
And here comes one.
A snake has found its way down one of those exit holes.
The workers flee in front of it, squeaking with alarm to rouse the soldiers.
With those formidable teeth,
the soldiers are capable of stabbing the snake to death,
and they block the tunnel.
(SQUEAKING)
Reinforcements arrive.
The snake thinks better of it.
The mother of the colony, the queen, is the only breeding female.
She gives birth to a dozen or so young at a time,
and produces a new litter every 13 weeks.
And she may live for 12 or 13 years.
The father of the brood is one or other of the two oldest soldiers.
He's not as long-lived as the queen.
A year or two of sexual activity seems to exhaust him and he dies.
His place will be taken by another senior soldier.
All these babies will become tunnellers.
Some will later graduate to being soldiers,
but none of the females, while the queen lives, will become sexually mature.
Why?
The colony has a communal latrine,
used by all, including the queen.
The workers, when they visit it, deliberately anoint their naked skin with its contents.
This gives them the colony's odour, so they are recognised and accepted by all.
But in doing that, they may commit themselves to a life of sterility,
for the queen's urine contains a substance
that helps to suppress the development of ovaries in others.
The supply of the fertility suppressant will continue
as long as the queen lives.
Only when she dies will one of the female soldiers mature sexually
and succeed to the throne.
The queen spends most of her life in her chamber surrounded by her soldiers.
She doesn't dig, she doesn't fight.
She concentrates her physical strength on producing within her belly
huge broods of babies.
So the ranks of the short-lived tunnellers
are maintained to continue the digging that's essential
to find food for themselves, their brothers and sisters and their queen.
These hard-working porters are also members of a society,
but one which numbers not a few dozen, but several million.
Nor are they just gathering straightforward food.
They're taking part in a much more complex agricultural system.
Leaf-cutting ants demolish plants morning, noon and night.
Heavy rain and direct sunshine are the only conditions that stop them.
Every one of these workers is female.
They're all sisters, working together in one of the most organised
and tightly-knit communities of all.
They use their legs as calipers,
guiding their jaws so that they cut a segment of a size
that is the most economical to cut and most practical to carry.
But they can't eat these leaf segments.
Cellulose, the main constituent of leaves apart from water, is very indigestible.
They have to take all these pieces back to their underground nest for treatment.
The journey may be down a tree trunk for 50 feet or more.
Once on the ground, it may still be 100 yards to the nest entrance.
And then further still to special chambers underground.
Here the leaves are taken over by a slightly smaller caste of worker,
who cut them into smaller segments still.
These chambers are subterranean gardens
where the colony cultivates a special fungus,
and the leaf segments are the raw material on which the fungus will grow.
But first, the segments must be processed.
It could be very damaging if bacteria or spores of an alien fungus
got into the nest and started to germinate like a weed.
So the workers meticulously clean the surface of each piece by licking it.
The edge of every segment is then chewed to prepare it for the next stage.
The garden chambers vary in size from an orange to a melon.
They're all filled with a honeycomb of grey, spongy material.
And now these smallest workers of all take over.
They're a mere two millimetres long, the size of a grain of sand.
Only these tiny dwarves can enter the minute spaces within the gardens.
They push the leaf fragments into the matrix
and then plant tufts of fungus all over their pulped surface.
Within 24 hours, the green of the leaf has almost completely disappeared
beneath a tissue of white threads.
A day or so later, the threads of fungus begin to develop tiny knobs at their ends.
This, at last, is the crop that the ants can eat.
One by one, the swollen ends of the threads are torn from the tangled mass.
Some workers consume it there and then.
Most is carried away to feed to developing grubs
and the other workers who laboured so hard gathering the leaf segments.
Slowly, the swarms of workers complete the harvest.
When the fungus is spent, its remains, and the mulch of leaves on which it grew,
must be cleared out of the garden.
The workers swarm all over the grey honeycomb, breaking it up.
Every particle is carried up the corridors and taken out of the nest.
Long processions of workers set off for the exits.
Here, in the open, by the side of the nest, is their refuse tip.
So one cycle of fungus cultivation is completed.
And the scale of their operations is enormous.
They can strip an entire tree of its leaves in a single night.
Their pathways extend for 100 yards in all directions.
The nest is 20 feet across and goes down for as much as 18 feet.
Inside, there are a thousand or so chambers
where the ants have their gardens and where they live.
And it's virtually impregnable.
Even the vibrations of my footsteps are enough to bring out the defenders.
These soldiers are 300 times heavier than the dwarves working in the gardens.
They bite any alien thing. Shoes, socks, anything.
Once they've fastened their jaws, they stay fastened,
even if the rest of their body gets torn off.
Soldiers are expendable.
Their task is to protect the one single individual in the colony
who is indispensible.
The queen, mother of all the members of the colony.
She is as big as a newborn mouse.
On her nuptial flight, she was impregnated by three or four males.
The sperm they gave her
lasts for the rest of her long and productive life.
The workers attend her continuously, collecting the eggs that she produces.
One appears, a tiny white bead.
A worker waits to pick it off and take it away to the nursery chambers.
The queen may lay a million a year.
Some are fertilised from her sperm store, others are not.
But all will hatch.
The grubs that develop from fertilised eggs
mostly become members of the exclusively female workforce.
The way they are fed by the workers
determines which of the six different castes they will be.
Unfertilised eggs develop into males,
who fly out of the nest to mate with young winged queens
and establish new colonies.
Once these ants start on adult life,
they will not be able to change roles, as mole rats or dwarf mongooses can.
Their destiny is fixed.
The first ants, back in the evolutionary past,
almost certainly operated as single individuals,
as many species of their wasp and bee relatives still do.
Over millions of years, they developed communities
of increasing size and complexity.
Now that process has come full circle.
By producing individuals specialised to do particular jobs in their society,
five million insects have become effectively one.
But what a superbly efficient one.
It's not the monkeys or the rodents
or, indeed, the human beings who dominate the forest.
It's the tiny ant that, by multiplying itself,
has turned itself into a super-organism,
a complex, highly disciplined society.