There's an insect in this garden
that all gardeners loathe...
aphids.
They've made enemies of gardeners,
but in the undergrowth they have friends...
ants.
Ants herd aphids to the best possible feeding places
just as human shepherds will herd their sheep to the best pastures.
And just as shepherds protect their flocks against wolves
so ants protect the aphids against their insect enemies.
Ladybirds are among the most dangerous. They, after all, eat aphids.
So the ants must get rid of them.
That's not easy. It's quite hard to get a grip on the polished shell of a ladybird.
But eventually, success.
Aphids excrete a liquid that ants relish, honeydew.
That's why ants protect them.
Such close relationships are frequent among insects,
perhaps because they've had so long to develop them.
They appeared on land, after all,
about a hundred million years before any backboned animal.
And they can also evolve much faster
because they can produce several generations within a single year.
So, perhaps it's not surprising
that they have developed relationships between one another
of a complexity that blows the mind.
These associations extend not only to other insects but to plants.
They were established at a very early period.
Plants are the basis of all life.
For only they can combine minerals in the ground with gases from the air
and produce something worth eating.
Insects, however, not only eat them
they also exploit them in much more devious ways.
Tropical rain forests are famous for being thick, tangled masses of vegetation.
But in this one, in Peru,
there are mysterious clearings
where only one or, at the most, two kinds of trees will grow.
The local people call such places as this Devil's Gardens
and believe that spirits kill other kinds of trees.
And the real killers of those trees?
Well, they've only just been discovered.
The leaves of the surviving trees
all have these swellings on their stems.
And going in and out are armies
of tiny, tiny ants.
The swellings are their homes.
Specially developed for them by the tree.
And in them, safe from predators, the ants keep their eggs and larvae.
They even keep domestic livestock,
white scale insects, which, like aphids, supply the ants with drinks of honeydew.
Producing this accommodation also benefits the tree,
for the ants provide their landlord with a valuable service.
They guard it against its enemies.
All kinds of insects will eat a plant's leaves given the chance.
But they don't get a chance, not on this tree.
So the caterpillar goes elsewhere.
This is a more formidable leaf muncher,
a kind of giant grasshopper,
several thousand times bigger than any individual ant.
That's not so easy to shift.
But it does have a weak spot.
If you can say that any insect has a heel,
then this one has an Achilles heel.
And the ants seem to know it.
Enough is enough.
The ants not only repel their host's animal enemies,
they also, perhaps more remarkably, keep competing plants at bay.
A squad of them leaves the barracks
and sets out on one of their regular patrols of the neighbourhood.
They've found a newly-sprouted sapling.
Perhaps it's grown from one of their landlord's seeds. In which case, all well and good.
But this one hasn't, it's an intruder.
They go into action, biting its stems.
Reinforcements arrive.
Hundreds of tiny jaws cut into its stems.
The sapling begins to wilt.
But bites alone are not enough for the ants to achieve their ends.
They lift their abdomens and inject formic acid into the crippled plant's wounds.
The poison spreads through the plant's tissues hastening its death.
And within a few days of being comprehensively stung,
all these plants are dead.
And the ants, or the "devils",
have extended their garden still further.
But the benefit of this drastic gardening, of course, is not restricted to the plants.
The ants also profit.
They have ensured that their plant landlord
can extend its territory without competition.
And that provides them with more homes, so they too can increase their numbers.
It's one thing to provide food and shelter in return for protection,
but it's quite another thing to be compelled to provide a home
where before there was none.
But some insects have the ability to force a plant to do just that.
They're called gall-makers and this oak tree is infested with them.
This odd wrinkled object at the base of an acorn, is known as a knopper gall.
Inside there is the tiny grub of a minute wasp.
To understand how it got there we have to go back to last spring.
This tiny insect, scarcely bigger than a mosquito,
is one of these gall wasps.
There are lots of them flying around the oak flowers.
Most of the flowers by now have been pollinated and are about to develop into acorns.
The gall wasps too have mated
and this female is looking for a place to lay her eggs.
She thrusts her ovipositor into the base of the fertilised flower,
and injects an egg.
And that triggers a profound genetic change in the growing oak bud.
It develops, not into an acorn but into something very different, a gall.
Within, the tiny larva whose secretions have caused the change
feeds on the oak tree's tissues.
As summer proceeds, the galls become increasingly hard and woody.
Autumn comes and the oak tree starts to shed its leaves.
It's shutting down for the winter.
And with its leaves go both acorns and galls.
Plant and insect life is suspended.
But unseen changes are nevertheless taking place.
Spring comes at last.
Inside the gall something starts moving.
The larva has turned into an adult wasp.
It has spent nine months within the oak tree's tissues.
It has only a few weeks of its life left.
Now as an adult it must look for another oak to inject with eggs.
A single oak tree may be afflicted by 70 different kinds of gall,
each produced by a different species of wasp,
and each with its own particular contorted shape.
These hard shells may seem to be effective defences for the little grub inside them,
but not necessarily so.
This is another kind of gall wasp
and she's not a genetic engineer, she's a burglar.
Behind her she trails her equipment for breaking and entering, a drill.
She carefully selects a site for her operations and takes aim.
She flicks away the drill's sheath and starts work.
Her aim has to be very accurate if she's to strike her target,
the larva at the gall centre.
The tip of her drill has a sharp cutting edge of metallic zinc
which pierces the gall tissues with ease.
When she detects that she's reached the central chamber,
a microscopic egg travels down the centre of the drill and into the larva.
The operation is over.
Her offspring will now hatch in the gall's centre,
consume the flesh of the resident larva and take over the gall.
Galls are worldwide.
California, for example, has other species of oak tree
and other kinds of gall.
These particular ones are relatively tiny, the size of peppercorns.
You'd hardly notice them except for one thing.
They jump.
And not only do they jump, they jump for three days.
The tiny larvae within flip themselves about inside their minute chambers.
Why they should do so is not clear.
Perhaps it's a way of moving their homes into cracks and crevices
where they're out of the reach of predators and parasites
and shaded from the hot Californian sun.
Another gall in Hungary protects itself in a more complex fashion.
It recruits insect guardians.
This gall is producing nectar.
It's sweet.
And it's producing it, not for the benefit of the oak tree,
but for the benefit of the tiny grub that lies within the gall.
Because the nectar attracts ants
and ants serve as defenders against any other intruders.
And if you want to see how valuable they are, let me remove some.
Within a few minutes a different kind of gall wasp appears.
It's another of those burglars looking for an existing gall
into which it can inject its egg.
But the ants have now returned and they attack the intruder.
Away it goes.
The ants, having driven off the wasp,
take their reward of nectar.
In the normal course of events, oak trees don't produce nectar,
but many plants certainly do.
It's a way of attracting insects
that will transport their pollen from one plant to another.
And the colourful flowers are advertisements proclaiming that nectar is there for the taking.
But the plants must also ensure that visiting insects
collect the pollen as well as nectar
and that leads to all kinds of complexities.
Like many plants, the pyramidal orchid has a way of ensuring that they do.
The burnet moth probes into the orchid's nectar store
and, as it does so, a horseshoe-shaped mass of pollen
clips on to its long proboscis.
Inconvenient it may be but the moth can't shift it.
Away it goes to another flower, taking the pollen with it.
And this time as it probes for a drink,
a speck of pollen is transferred to the female part of the flower.
The job is done.
The traffic of insect pollinators to and from flowers is so heavy
and, in particular, so predictable,
that it's not surprising that some invertebrates have learnt to exploit it.
A white crab spider sits almost invisible on a white flower, waiting in ambush.
And it catches a bee.
The spider is clearly taking advantage of the flower's advertising.
It looks superbly camouflaged to our eyes,
but insect eyes are different to ours
and see parts of the light spectrum invisible to us.
Under ultraviolet light we can get a better idea of how they see things,
and most surprisingly the spider looks more obvious to them than it does to us.
Why should that be?
Perhaps it's because ultraviolet markings on some flowers
serve to guide insects to nectar.
So maybe the spider's colour is a positive attraction for bees.
Certainly, honeybees seem more likely to visit flowers
with crab spiders on them than those without,
often with fatal consequences.
The relationships between the animals that live in the undergrowth
are full of such deceits and impostures.
Here in Australia there's an intriguing example
that has only just been discovered.
This...
is a feather-legged bug.
It too manages to persuade prey to come close.
But its invitations are aimed not at bees, but ants
and what the ants get is a very nasty surprise.
Like all members of the bug family,
this one has a long tube for a mouth.
Most stick it into plants to suck sap.
Using it to eat an ant is more difficult.
The bug starts by waving to passing ants.
The feathery flanges on its legs are so large they can be seen from quite a distance.
The ants are visibly intrigued,
but they're not yet close enough for the bug to attack.
So it reinforces its gestures
by producing a chemical perfume that the ants find irresistible.
They come closer still.
They climb all over the bug,
trying to find the source of this strange compulsive smell,
and the bug does nothing to stop them.
Where does that smell come from?
Is it on the bug's legs?
The bug now answers the ants' questions.
It lifts itself up and reveals a gland on its underside.
That's what's producing the smell.
The ant presses its head against the bug's chest
to actually taste the gland.
It's the perfect position for its own execution.
The bug stabs its mouth into the back of the ant's head.
So a tube can be used to suck nourishment from an insect,
as well as from a plant.
This is the rogue of the bug family, a killer.
Ants are among the most numerous, widespread
and frequently exploited members of the undergrowth.
These, in Australia, collect seeds and store them underground.
Plants encourage them to do so
by adding a tasty capsule to their seeds.
That may seem odd, but these ants don't eat all the seeds they store.
In fact, seeds are more likely to germinate below ground than above.
But not everything on this forest floor is what it seems.
When it comes to putting your eggs in a suitable place,
some insects persuade other insects to do the job for them.
This little object looks like a seed,
and certainly, it's fallen from above,
and that ant seems to think it's worth eating.
But actually, it hasn't come from a plant, it's come from another insect.
And this is it.
It's rather difficult to see because it looks exactly like a dried leaf,
but it's a stick insect.
There's its head, antennae, and that's the tip of its abdomen.
As an adult, like this, it spends all its time up in the trees eating leaves.
And when the time comes to lay, and this one is doing so,
all she does is simply to flick away the egg, and let it fall to the ground.
But that's not quite as risky as you might think.
Wherever you are, you can be pretty sure that some ants will turn up looking for food.
And that is exactly what the stick insect's eggs look like.
A nutritious seed, complete with that fatty capsule at the tip.
So the ants start to haul them away.
Although the ants certainly eat a great number of the seeds they store,
stick insect eggs don't seem to be quite as tempting.
At any rate, the ants, after all their labour,
usually leave the stick insect eggs untouched.
While the seasons pass, the eggs lie underground,
hidden from birds and any other predators that might eat them.
They may remain there, safe, for up to three years,
but eventually they hatch.
It's only at this early stage of its life
that a stick insect actually runs.
The youngsters positively scamper up into the tree branches.
There they will take up their adult life of leisure,
well-camouflaged, stolidly chewing leaves.
Giving your offspring a good start in life can take a lot of effort.
So some insects have evolved highly complex strategies
to induce other species to become nursemaids on their behalf.
This Californian desert hardly seems to be the best place to find nursemaids.
But blister beetles have an amazing way of discovering them.
It starts simply enough with the female beetle.
She has dug a hole and is now laying her eggs in it.
That done, she abandons them.
A few centimetres below the surface of the sand conditions are good for eggs.
Not too cold, neither too hot, even in the heat of the day.
Six weeks later, they hatch.
But these sands are very barren and scorching hot.
Somehow the tiny larvae have got to find food
and they won't find it here.
Their survival depends on teamwork.
Together, as a closely coordinated group,
they climb up a stem of withered grass.
When they get to the top, there's nowhere else to go.
They look dangerously exposed to the sun and to other predators,
but there they stay, in a tight squirming mass.
For those that can get there,
the top of this stem has become a stage for a remarkable piece of deception.
What these larvae want is a lift, a ride.
And they want it so badly that sometimes they'll even try and get it from a human finger.
But what they're really searching for is not a human finger.
They're searching for another insect.
Here it comes. A female digger bee
leaving a tunnel that she's just dug for her own young.
She's off to gather pollen.
She packs it into baskets on her back legs
and takes it back to her burrow.
It'll provide valuable food for her young when they eventually hatch.
And here comes a male. He's on the lookout for a female.
To him, the cluster not only looks like a female, it smells like a female.
For the beetle larvae are producing a perfume, a pheromone,
that is exactly like that emitted by a female bee.
He alights in order to mate, and in seconds is covered by the larvae
that swarm all over him.
At first, he seems stunned by the shock of his sudden increase in weight.
But then he's off again.
Now his luck improves. This really is a female.
And while he mates, his passengers jump ship.
Now they're all on board a female bee.
She, having mated, goes back to her nest to lay,
taking the larvae with her.
At last, the young beetle larvae have reached safety and food,
the store of pollen that the female digger bee worked so hard to collect
for her own young.
So they hop off and tuck in.
Not only do they consume the pollen,
when that runs out, they'll eat the young bee larvae, too.
Blister beetles are not alone in using couriers to take their offspring to food.
The young of this botfly, here in Brazil,
feed on the blood and tissues of living cows.
But how is a female to get them there?
She is a big insect. So big that cows would notice if she landed on them,
and would probably flick her off.
She needs a lightweight courier.
A housefly, a fraction of her weight. That will do nicely.
She drops down to stalk it.
She's got it.
She manipulates the housefly into the right position.
And now, one by one, she glues her eggs onto the housefly's abdomen.
Within a few seconds,
the housefly has been coated by about 30 cream-coloured eggs.
The botfly releases its hapless messenger.
The housefly seems well aware that it's carrying an extra load
but it can't get rid of it.
So, it goes back to its normal business
which includes visiting cows to drink their sweat.
A small fly, unlike the lumbering botfly, is no real irritation
and is able to feed largely unhindered.
The fly mops up the sweat with its pad-shaped mouth parts.
But as it feeds,
so the warmth of the cow's body causes the botfly's eggs to hatch.
The larvae are armed with tiny hooks
which help them get a grip on a cow's skin and bore into it.
So in a few minutes, a cow can acquire a dozen botfly larvae,
feeding away beneath its skin.
Licking won't get rid of them now.
A couple of months later, the full-grown larvae emerge and drop to the ground.
There they will burrow into the soil, pupate and turn into adults.
All kinds of creatures, great and small,
are exploited by insect parents in this kind of way.
This is Costa Rica.
And here lives a species of orchard spider.
They construct horizontal orb-webs
as lovely as those made by any spider.
But one individual has a hanger-on.
An anonymous looking grub is clinging to her abdomen.
She seems little affected by having a passenger.
And every day, as usual, she builds a new and perfect web.
She is just as efficient a hunter as ever
but every catch she makes, she shares, in effect, with her passenger.
For the grub is sucking her juices.
Her passenger stays with her for some two weeks,
slowly growing in size, at her expense.
And still, daily, she constructs a new web.
Then, one evening when, as usual, as she starts to spin,
something seems to have gone dramatically wrong.
She seems incapable of making her normal, beautiful orb.
What she produces has no shape, no radiating spokes, no sticky spiral.
It's just an untidy tangle.
The grub is responsible.
It has injected her with a hormone
that has spread to her brain and deranged her.
She has only an hour or so to live.
This is her last act.
Small claspers inflate on the grub's back.
With these it grasps the wreckage of the web
so that it will not fall as the dying spider loses her grip.
It sucks the remaining fluid from the spider's body.
Slowly the liquid is withdrawn.
Even the spider's legs are emptied
until the corpse is no more than a husk.
The grub has no further use for it.
And now the grub, clinging to the spider's last tangled web,
starts to spin for itself.
It needs a shelter in which to reorganise its body.
A cocoon.
Inside the lacy walls its body is breaking down,
for it has to be reassembled in a very different form.
At last the killer is about to reveal its true identity.
It's a wasp.
Now it must fly off to find a mate,
so that another wasp egg may be attached to another orchard spider.
The opportunity to find creatures to parasitize in the undergrowth
seem almost endless
and yet, surprisingly, there are some parasitic wasps
that find their victims in water,
in lakes and ponds like this one.
They're extremely small, about a quarter of a millimetre long,
in fact, one of the smallest of all insects.
And I've got some in this test tube.
And to give you an idea of just how small they are,
I'll drop this pin in alongside them to give a sense of scale.
Yet, these tiny specks have eyes, legs, feelers just like any other insect.
They're known as fairy wasps,
and spend nearly all their lives underwater.
They make a tiny water flea, itself only the size of a grain of sand,
look like a giant.
They're so minute
they can lay their eggs inside the eggs of other insects.
And they choose those laid by water beetles.
Water beetles lay their eggs inside plant stems.
A female fairy wasp, having located one,
uses its microscopically-thin ovipositor to inject up to 100 or so eggs
into just one of the beetle's.
And here they hatch.
The young wasps feed and grow,
consuming the water beetle's undeveloped young.
Not only that, they mate here.
Then, at last, they leave the shell of the beetle's egg.
The females must now lay.
And some will be able to do so in other ponds,
because, in spite of everything, they still have wings.
Other bigger parasitic wasps have totally lost their wings.
You can find them on many a British heath.
This one, Methoca, looks rather like an ant,
and insects that live by hunting ants easily mistake it for one.
The tiger beetle is a very active ant hunter.
It chases them and runs them down.
And very successful it is.
Earlier in its life, of course, as a larva a tiger beetle can't run around.
Instead the larva catches ants by waiting in ambush.
It plugs the entrance to its burrow with its armoured, plate-like head.
If an ant touches that, it's as good as dead.
It works every time.
Methoca, however, is a more awkward customer.
The beetle larva is waiting with jaws agape.
But Methoca is more agile than the usual ant
and it manages to slip out between the beetle larva's jaws.
It grabs the larva's soft body and pulls.
And now it stings it.
Methoca climbs out of the tunnel waiting for the poison to take effect.
The sting has only paralysed the larva
and the wasp drags the helpless creature farther down its burrow.
Now she lays her egg onto it.
To prevent anything interfering with her grub while it stays underground
feeding on the paralysed beetle larva,
she blocks up the entrance.
This is the longest and most laborious part of her motherly duties.
But now, without any more work from her,
her young will have all the food it needs to develop into an adult.
Underground nests are certainly among the best protected of all insect nurseries
and, indeed, they are very difficult for parasites to break into.
Ants defend their colonies against intruders with great ferocity.
And yet, here in this meadow in central Europe,
there are ants' nests where intruders live undetected.
And there's one right here.
This is the caterpillar...
of the blue butterfly
and it's lived in this nest undetected
and protected by the ants and fed by them for the last two years.
Indeed, it's been so thoroughly accepted by the ants
that they will try and rescue it in preference to the young of their own queen.
As in fact they are doing right now.
But how do these caterpillars get into the ants' nest in the first place?
Alcon blue butterflies begin their courtship in June and July.
They are surely one of the loveliest sights of a European summer
as they flutter and flirt among the flowers of the meadow.
Male and female meet...
and join.
Once they have mated
the female Alcon blue must find a gentian plant.
Here she lays her eggs.
The caterpillars, when they hatch, stay feeding on the gentian for a couple of weeks.
But eventually they fall to the ground.
There are ants everywhere in a meadow like this, and they soon find it.
It smells just like one of their own larvae
and they start to haul it back to where one of their larvae should be,
in their nest.
Other foragers from the same nest have found another.
During the next few weeks, as many as half a dozen may be taken back to the nest.
Here they are hauled down to the nursery chambers
and put with the ants' other eggs and larvae.
And because the caterpillars continue to produce a pheromone
exactly like that produced by the young ants themselves,
they are treated as if they were young ants.
Even though they are bigger and a different colour.
The caterpillars even mimic the sound the ants make
when they beg for food,
so the workers dutifully feed and clean them.
You might think that this caterpillar has protected itself very well
by deceiving these ants.
But life in the undergrowth is full of surprises.
An ichneumon wasp.
It too, like the blue butterfly,
wants to get its young into an ants' nest.
But not merely as lodgers.
It has a more sinister intention.
Somehow or other, in a meadow full of ants' nests,
it can detect which one harbours a butterfly caterpillar,
and this, it decides, is one of those.
Once inside, the ants start to attack it, as you might expect.
But then, the ants' behaviour changes. There is pandemonium.
The wasp has released a pheromone that makes the ants attack one another.
With the defenders fighting among themselves, the wasp is able to go deeper into the nest.
It's reached the nursery and here lie the caterpillars.
Now they are defenceless.
The wasp sets about injecting each of them with an egg.
A few ants do their best to prevent this.
But there is no real opposition.
While most of the ants continue to fight among themselves,
the wasp finds a second caterpillar.
Another egg is laid.
The wasp leaves.
With the wasp gone, the ant colony slowly returns to normal.
The caterpillars are still there, alive and apparently well,
and the ants continue to care for them.
Once the caterpillars are fully grown,
each starts to construct a chrysalis,
which all butterflies need as a protection while they turn themselves into adults.
Each chrysalis is cleaned and protected by the ants
as if it were one of their own pupae.
One begins to hatch.
Out of it comes, yes...
a blue butterfly.
It leaves its foster home.
Out in the open its limp wings can expand.
And now it's ready to flutter and flirt just as its parents did.
And the ants are still bewitched by the traces of pheromone
clinging to the empty shell the butterfly leaves behind.
But there are still others in the nest as yet unhatched.
And out of this one comes, not a butterfly,
but a wasp.
Hardwired into the microscopic brain of this ordinary-looking insect
are a whole series of skills, sensitivities and reactions
that will enable it, in its turn,
to give its own offspring a special start in life.
It can detect what the ants themselves find undetectable.
It can tell the difference between an ant larva and the butterfly larva.
What is more, in a meadow of 100 ants' nests,
it will be able to find the one that contains the butterfly caterpillar.
How it does it, we have no idea.
So it seems that among the animals of the undergrowth
there are many beneficial partnerships.
But exploitation and deception can work just as well.