Living Together The Trials of Life

Rajasthan, central India.

The day is warming up, and the animal community is in a relaxed mood.

Sambar deer are cooling themselves in the shallows of the lake,

looking for greenery to nibble, and tolerantly taking the egrets for a ride.

The egrets, too, are finding a little to eat insects, perhaps, picked out of the deer's coat.

Nature isn't always red in tooth and claw.

Different kinds of animals are often regular companions and get on well with one another.

Langur monkeys finish their morning meal of leaves.

They are fussy, untidy eaters.

They drop a lot of the leaves,

either by accident, or because they don't fancy those particular ones.

And that suits the spotted deer.

At this time of the dry season, the ground is parched and greenery worth eating is very scarce.

The smallest fragment of vegetation fallen from above is worth having.

The deer follow the monkeys from tree to tree,

picking up leaves that, by themselves, they couldn't reach.

The monkeys also benefit from the presence of the deer.

They sometimes come down to forage on the ground, and there, they are vulnerable.

Deer have a keener sense of smell than the monkeys.

They detect dangers that the monkeys can't see, and stamp a warning.

We ourselves have very few such relationships, voluntarily, with other species of animals,

except with those animals that we have domesticated and enslaved.

But back in our evolutionary past, we had many.

Today we think we are so powerful, or so detached from nature, that we think we no longer need them.

But in the natural world at large those relationships are widespread.

Some have existed for long enough to transform the animals' bodies.

Some are only just forming.

This species of goby, for example, that lives around coral reefs,

has probably recently struck up a relationship with a shrimp.

The two regularly live together, sharing the same hole.

But the goby plays no part in making it.

It's dug entirely by the shrimp.

The shrimp, in fact, seems to be a compulsive excavator,

never content with its home, always making improvements and digging extensions.

And the goby doesn't help.

In fact, if anything, it gets in the way.

But it's an essential companion for the shrimp,

for this species of shrimp is virtually blind.

The goby, on the other hand, has excellent eyesight.

It's always on the alert.

The shrimp, as it works, keeps in touch literally

by continually flicking one of its long antennae over the fish

to make sure that it's still there.

As long as the goby is out of the burrow,

then the shrimp knows that it's safe to carry on working.

The goby, naturally, is always on the lookout for something to eat,

and may have to make little excursions to get it.

A tiny edible morsel that floated by.

But even while it's feeding,

the shrimp's antenna is still in touch with it.

Danger. When the watchman retreats to safety, so does the shrimp.

The goby, having fed, seems content to remain in the hole. Why expose yourself to danger unnecessarily?

But the shrimp is perpetually keen to work

and appears to hustle the goby to persuade it to go out again.

The shrimp collects its food from a little patch of alga that grows beside the burrow entrance.

It knows just where that is,

so it can nip across quickly and snatch a few clawfuls with the minimum of risk.

All is well as long as the shrimp keeps in touch with the goby.

If not, there can be trouble.

That was an anemone it blundered into, and it beats a swift retreat.

For a moment, it seems lost.

Then the goby comes over and contact is re-established.

The partners are together again and all is well.

So two very different animals operate a partnership.

The blind landlord provides accommodation. The tenant provides a guidance service.

Hermit crabs live in a different kind of home.

Instead of a hole, an empty shell.

They, too, can find themselves with lodgers.

This one's companion is a ragworm.

For the worm, this is a good place.

It has an excellent home, where it's safe from predators,

curled up inside the shell alongside the crab's abdomen.

And on its very doorstep there's a regular supply of food brought there by the crab.

Nonetheless, collecting a share of that food seems a risky business!

The crab's mandibles could easily chop the worm's head off.

But the worm has had a lot of practice at this sort of thing.

Whether the crab benefits from the arrangement is rather doubtful.

But there's not much it can do to get rid of its lodger anyway.

A small octopus. Hermit crabs are one of its favourite foods.

In the centre of those writhing arms it has a powerful beak

with which it can drag the crab from its shell.

And that's the end of both the hermit crab AND its lodger.

But this species of hermit crab recruits a bodyguard.

Anemones have stings in their tentacles stings that are quite strong enough to repel an octopus.

Since the crab wanders about a lot, its bodyguard to be any good has to travel with it.

It's not easy to unstick an anemone from a rock. The crab knows how.

You have to tickle it around the edge of its bottom.

You can tell that the anemone isn't particularly alarmed by this

because it hasn't closed up and is still waving its tentacles.

That makes three guardian anemones on the crab's shell,

but is that enough to give it protection?

The octopus is not sure.

No, it's not worth it.

So the crab has its bodyguards,

and its bodyguards, for wages, get bits and pieces that float by when the crab chews up its meals.

It's not always easy to decide which partner is exploiting which.

The balance of advantage is often very delicate.

Take these ants, in Australia.

They are ferocious, and normally they'll rip apart any caterpillar.

But see how they treat THIS one.

The caterpillar has on its back a number of little nipples

which apparently fascinate the ants.

One, near its back end, when stimulated by an ant, produces a drop of liquid

honeydew, which the ant drinks.

As the caterpillar grazes on leaves, the ants keep continuous guard over it,

threatening anything that comes near it, so that even birds don't attack it.

The caterpillar must make sure that the ants don't forget what kind of caterpillar they are dealing with.

If they think it's any other kind, they will tear it apart and eat it.

So the caterpillar regularly makes a characteristic buzzing vibration.

And on either side of the honeydew nipple there are two others.

From these sprout tentacles which apparently release a pheromone

a kind of perfume that keeps the ants unaggressive.

Tree ants build nests almost as big as footballs from the leaves of the tree.

And they feed on any small creature that happens to land in the tree.

This grasshopper had little chance.

As soon as it landed, they set upon it.

Now they are butchering it and carrying it back, piece by piece, to their nest.

As well as this nest, the workers construct small shelters.

First, a team bridges two leaves

and slowly pulls them together.

Others bring grubs which they squeeze, to produce a sticky silk.

By passing the grubs back and forth, they weave a fabric that holds the two leaves together.

It's a shelter for the caterpillar.

When it's complete, they guide the caterpillar into it.

Once in its shed, it will be safe for the night.

The ants look after it like farmers looking after a dairy cow.

Their cow, in return, provides them with food.

So, at this stage, neither ant nor caterpillar seems to have the advantage.

But this same species of ferocious stinging ant also has a partnership with another species of caterpillar

and there the result is different.

This one has a glossy, horny shield on its back.

It, entirely of its own accord, marches right into the ants' nest,

undeterred by the ants' threatening postures and sprays of formic acid.

No matter what the ants do, they can't stop it.

Deeper and deeper it goes, through the corridors of sewn leaves, right into the heart of the nest.

It reaches the queen. If she is killed, the whole colony will die.

But she is not what it is looking for.

The soldiers make little impression on the caterpillar's armour.

Neither can they get underneath it to reach the soft, vulnerable body.

On it goes, until it reaches the nursery chambers,

where the developing grubs lie.

Try as they might, they can't lift the shield sufficiently to enable other defenders to get beneath.

With the intruder actually within the nursery, the workers become totally confused.

Some try to carry off the grubs to safety elsewhere.

They can't do it quickly enough.

The caterpillar snatches a grub and pulls it under the shield.

Then, secure beneath its armour,

it slowly eats it.

As the season progresses, several of these armoured intruders make their way into the nest,

and there gorge themselves on ant grubs.

After some weeks, the caterpillars have eaten all the grubs they need to grow to their full size.

Now, in the heart of the nest, they are ready to turn into butterflies.

But how can a butterfly get past the ants? Surely they have a chance for revenge.

Slowly, the insect hauls itself out of its horny armour.

But it's a strange sort of butterfly that emerges.

It's covered in scales that are so slippery that the ants can't get a proper grip on them.

Those that DO manage to bite

get their jaws covered with a sort of fluff that they clearly find intensely irritating.

So, at last, the murderous lodger goes free.

Ants and caterpillars, like crabs and anemones, are about the same size.

If a lodger is much smaller than its landlord, it tends to live, not so much WITH it, as ON it.

Those monkeys over there, for example.

They've got a number of tiny passengers.

Like most mammals with hairy coats, they've got fleas.

When fleas bite and suck blood, they itch.

It may be necessary to get a friend to help pick them out from parts that you yourself cannot reach.

This is not fur, but the fabric of a bird's nest. Fleas live here too.

A young starling, within two days of hatching, is likely to have several dozen fleas.

Fleas have six legs, like all insects, but no wings.

Those would be an encumbrance to crawling about in fur and feathers.

Instead, they have powerful hind legs that enable them to jump onto their host.

Their jaws have become specialised for sucking blood.

They feed on nothing else. They HAVE to live on another animal.

They contribute nothing to its welfare. This is not a partnership, it's parasitism.

Nor are fleas the only parasites in a bird's nest. Lice are there, eating feathers.

They, too, are insects, and any one bird may have up to a dozen different kinds,

each living on, and eating, a different kind of feather on the neck, the wings or the head.

Insects seem to have a particular flair for parasitism.

Each of their main families has some members who have taken it up.

But insects themselves can also be parasitised.

This nest of bees has been invaded by mites tiny cousins of spiders.

They are so tiny that several hundred of them can sit on the leg of a bee.

And they, too, itch.

They get everywhere, and once they have found their way into a colony, they spread to every member of it.

Mites are just as specialised as feather lice.

These bee mites live only on this particular species of bumble bee.

And this flower, milkweed, is a staging-post for one of the most specialised mites of all.

Moths come to feed on the milkweed at night,

dipping their long, threadlike tongues deep into the heart of the flowers to sip the nectar.

But this moth is already infested with mites.

Its ear, a tiny hole in the side of its head, has become the home of a whole colony of them.

And a new colonist awaits on the flower itself.

While the moth drinks, the mite crawls up its tongue.

Once on the moth's head, it knows which direction to take through the jungle of fur to reach the ear.

There is a danger in this. Blocking up an ear makes it useless to the moth.

If the moth can't hear, it can't avoid the bats that hunt it.

That would be disastrous for moth AND mites.

So the mites occupy only one ear, and always leave the other free.

They use one part of the ear-tube for stacking their droppings,

another for laying their eggs, and yet another for rearing grubs.

How do their offspring find another of these homes?

Why, of course, by clambering down their host's tongue as it drinks,

and waiting on the flower for another moth of the same species to turn up.

But parasites are themselves preyed on.

This little mouse lives in Central America

and regularly carries a dozen or so passengers wriggling around in its fur.

They are beetles, and they were once thought to be parasites that sucked the mouse's blood,

for they have large and powerful jaws.

But the mice carrying most beetles are not the most anaemic, as you might expect.

They seem to be the most healthy.

The mouse's most serious parasites

are, in fact, here in the lining of the nest

fleas and ticks that DO suck its blood.

Each mouse has several holes in the forest,

and ALL are likely to be infested.

When a mouse settles down in one,

the beetles drop off and go hunting for the fleas in the nest lining.

So the beetles, far from injuring a mouse, actually aid it.

Got one!

As far as a beetle is concerned,

the mouse is a convenient transport system for getting from one rich hunting-ground to another.

The mouse that carries most beetles has the most comfortable life.

These birds hunt parasites. They're finches from the Galapagos Islands.

And the creatures they help the giant tortoises.

You can hardly scratch yourself

if you have legs like these!

Yet tortoises, like so many other animals, are pestered by skin parasites, especially ticks.

The finches eat mainly seeds.

But ticks, apparently, make a welcome change.

When there's a tortoise nearby and the finches want a meal with a difference,

they signal to the tortoise by jumping up and down in front of it.

The tortoise reacts to the finches' advances in a remarkable way.

It stiffens its legs so that its huge body is lifted clear of the ground, and cranes up its neck.

The invitation is unmistakable.

There's no way that the tortoise could pick off parasites

from the places that these attendants manage to reach.

A few minutes' servicing by the finches is enough

to clear the tortoise of most of its pests.

Another satisfied customer!

Fish have the same sort of problem, and the same sort of solution.

The huge manta ray is troubled by sea lice and parasitic barnacles that burrow into its skin.

But it has other company an attendant fleet of small fish that travel with it.

When the opportunity arises, they swim over their host's body, even inside its gaping mouth,

picking off the passengers.

Like the giant tortoises, fish with skin problems patronise regular cleaning establishments.

This grouper hangs in the water at this special place on the reef,

and small wrasse that have been waiting amongst the coral swim out and start fussing around it.

They even dare to swim inside the huge jaws.

It's not only fish that work as cleaners.

This moray eel is being tended by a shrimp.

Open wide, please!

Amazingly, the cleaners are never harmed...

..even though they tickle!

These shrimps are quite large big enough to make a good meal

but they're never injured, either.

Regular customers return to these cleaning-stations every few days.

Although the resident staff of wrasse and shrimps can deal with as many as fifty an hour,

there are often queues of itchy fish waiting their turn.

Some fish, however, have their own personal valets.

Sucker-fish, or remoras, have got a fin on their back that has been modified into a sucker so powerful

that it's almost impossible to pull one off if it wants to stay on.

They travel with their host wherever it goes,

picking off parasites whenever there's an opportunity to do so.

Giraffe, like many other big game animals in Africa,

also have their own personal staff.

Ox-peckers live almost permanently on the bodies of their hosts,

scuttling about all over it.

On this spacious, patterned stage

they act out most of their lives.

Here, they argue, court, and feed their newly-fledged young.

True, they can't nest here. They do that in holes in trees.

But they line those holes with giraffe hair, so they'll feel at home.

Their claws are so long

that they can cling in almost any position and move in any direction.

Their flat beak slips easily between the hairs,

as they scissor through it, searching for ticks.

And they get everywhere, on young and on old.

Even when the animal moves off, they will hang on

with the skill and unconcern of accomplished jockeys.

Ox-peckers are a mixed blessing.

The ticks they eat are full of blood,

but sometimes they take that blood directly from an open wound.

By doing that, they don't improve the host's health, but damage it.

They keep the wound open long after it would otherwise have healed.

Even so, without them, giraffes would be more seriously troubled by skin parasites than they are.

We ourselves, of course, can also get infested with ticks and fleas if we're not careful.

They're everywhere, particularly in the rainforest.

One has a reasonable chance of getting rid of animals that settle on your outside.

I can flick off these ticks.

If YOU can't do it, an ox-pecker or cleaner-fish may do it for you.

But if the parasite manages to get actually inside your body, that's a very different matter.

The corridors and chambers of an animal's digestive system

offer great advantages to any creature that can dwell in them.

Inside here they are secure from enemies,

and washed by a nutritious soup that their host has already chewed, mashed and partially digested.

All they have to do is to absorb it through their skin.

They don't even need a mouth.

The animals that are best suited to this interior life

are those long, spineless, legless creatures we call worms.

Flat, ribbon-shaped tapeworms hang onto the walls of the gut

with a crown of hooks that encircles their head.

In the corridors of the intestines, roundworms proliferate.

Every backboned animal that has been examined, whether fish, amphibian, reptile, bird or mammal,

proves to be the host of a roundworm.

These, living in a gut, merely rob the host of some of its food.

But they may spread to cause severe damage to the liver and the lungs.

Other roundworms, too, cause serious problems.

Some, as thin as threads of cotton, swim along the blood-vessels and collect in the heart-valves,

blocking them so seriously that their host dies.

The young of such threadworms, swimming around in the bloodstream,

depend on biting insects to transfer them to another host.

During the day they swim in blood-vessels deep within the body,

but at night they move up into the capilliaries beneath the skin.

So when a mosquito sucks their host's blood, they are taken up.

They grow inside the mosquito and when it bites some other animal

they are transferred into a new host, a new home.

Others, smaller still, that wriggle among the blood corpuscles,

belong to the most ancient of all animal groups the protozoons.

They first got inside animals so long ago that most of their hosts have developed an immunity to them.

Human beings have not yet done so, and in THEM they cause sleeping sickness and death.

Internal parasites have a problem getting their offspring into another host.

Tiny ones may use biting insects.

Bigger ones, like this roundworm, have to use other methods.

The first stage getting their eggs to the outside world is easy.

This roundworm, full of eggs, sheds them into its host's gut,

so that they fall out with its droppings.

Once in the soil, they may lie dormant for some considerable time.

When conditions are suitable temperature just right and moisture reasonable they begin to hatch.

The tiny worms crawl up leaves of grass,

and await the moment when a hungry mouth will crop the grass,

carrying them into another stomach.

Transfers are not always simple. The complexities of some routes are almost beyond imagining.

Denmark. A morning in summer.

There has been a shower of rain.

Meadows and woodlands are drenched.

Snails are slowly crawling around through the wet leaves, grazing.

They are feeding on algae and rotting vegetable matter.

Early morning is the best time for them. The sun is not yet hot enough to dry them out.

They can explore parts of the vegetation they can't reach at other times.

But this one is different from the others.

Its left tentacle is swollen and pulsating. It has a parasite.

A few months ago, the snail took in, along with normal food, some bird droppings.

They contained the eggs of a fluke that was living in the bird's gut.

They hatched and the parasite grew, taking over the snail's body.

As the sun shines brighter,

the parasite extends a striped muscular bag packed with tiny larvae into the snail's tentacle.

It nearly always picks the left one.

Birds rarely eat whole snails. They are too big, and few can extract them from their shells.

But the larvae must reach the body of another bird to develop further.

The presence of the parasite changes the snail's behaviour.

As the day wears on, it does not, like uninfected snails, crawl into the undergrowth, out of harm's way.

Instead, it remains exposed, out in the open dangerously so.

Now there is a parasite in each tentacle.

Perhaps they look like caterpillars or tasty worms. Maybe they just look odd.

But certainly, the fly-catcher finds them interesting.

The connection has been made. The circle is complete.

Another bird has become infected.

Inside the bird, the striped bag releases its multitudes of larvae.

They move through the bird's body and take up residence in its gut.

And the whole cycle starts all over again.

Flukes are related to the flatworms that live independently in ponds.

But they found their greatest success as internal parasites.

Some reside in the liver. Other kinds anchor themselves in the bladder, lungs or gut.

Most are capable of causing serious disease.

But not all internal parasites injure their hosts. Some help them.

These microscopic organisms

undoubtedly alive and arguably animals, since they don't have chlorophyll to manufacture food

live in the stomachs of most animals.

They can break down cellulose the substance of most plant tissue.

That's something the digestive juices of most animals can't do.

Their free-living ancestors swam in ponds, as some of their relatives still do today.

These are members of the family that have simply found a warmer, darker pond.

This pond is extraordinarily rich in edible material. It's a stomach.

So a buffalo, like most wild animals, is not, as it might appear, a single individual.

It's a walking zoo.

Its ox-pecker friends are obvious, but if we looked closer, we would find ticks boring into its skin.

In its mouth, leeches it picked up when it drank from the river.

Tapeworms trail through its guts.

Flukes are moored in its liver.

Protozoons swim in its blood and swill around in its stomach.

It's a community of animals that have been committed by evolution,

for better or for worse, in sickness and in health,

to live together.