02 Taking to the Air | BBC Life in the Undergrowth
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00:30A summer evening on the Corrush River in central Europe.
00:36Its waters are mirror smooth, but on this particular day of the year, all that is about
00:41to change.
00:45Giant mayflies, Europe's largest, are starting to rise to the surface and struggle out of
00:51the skins in which they lived as larvae.
01:00At first they come in ones and twos.
01:03Soon there will be millions.
01:12For two years they've lived underwater.
01:14Now they must fly to find a mate.
01:17This should be the climax of their lives.
01:27The first to appear are quickly taken by predators.
01:37But soon the swarms are so huge that neither fish nor birds can make any impact on them.
01:43The first mayflies to emerge in this mass hatching on this river in Hungary are all
01:49males.
01:50As soon as they free themselves from the larval skin on the surface, they take off and seek
01:56safety in the banks.
01:58And there they hang in trees and bushes, or indeed on my finger.
02:03And the reason they have to rest like this is because they still have to make one final
02:09molt.
02:16Their wings that were transparent now have a handsome blue tinge, and the elegant filaments
02:22at the end of their abdomens are even longer than before.
02:34They're looking for mates, but they have a problem.
02:38They can't feed, for they have neither mouth nor stomach.
02:41They have to fuel their flight entirely from the reserves of fat that they built up when
02:46they were larvae feeding in the river.
02:50But that fat will only last them for about half an hour of flight time.
02:56So the race to mate now becomes a frantic one.
03:02The females begin to rise to the surface, and the males fly up and down the river searching
03:08for them.
03:14As soon as they find one, they all pounce on her, competing to be the one to fertilize
03:18her eggs.
03:27But the struggle of doing so saps their limited energy.
03:37Before long, they begin to run out of fuel, and though they flutter despairingly, they
03:41can't maintain themselves in the air.
03:50Win or lose, their lives are almost over, and dead bodies start to litter the surface
03:56of the water.
04:01But the females are still in the air.
04:04They're flying upstream, judging the depth of the river and the currents in it to find
04:11a place where they can lay their eggs so that they will float back downriver to the same
04:17sort of place where the adults themselves lived as larvae.
04:24The ancestral mayflies were among the first creatures of any kind to take to the air about
04:29320 million years ago.
04:32For them, as for their living descendants, flight was a brief but invaluable way of finding
04:38a mate and expanding their breeding territories.
04:42The river has also been the home of another kind of insect with an equally ancient ancestry,
04:48and it too is beginning to emerge from the water.
04:53Bigger and more ferocious than the mayfly larvae, it has been feeding on tadpoles and
04:58even small fish.
05:00But that phase of its life is over.
05:04Now each one has to haul itself out of the water and into the air.
05:09On the top of its thorax, it carries a bulging backpack.
05:23It hunches itself and its outer skin splits.
05:29A very different creature begins to appear.
05:34White threads are drawn out of its flanks.
05:36They are the linings of thin tubes that penetrate deep into its body, air tubes that will enable
05:42the insect to breathe now that it is out of water.
05:53It gulps air, inflating its body, forcing fluid into the bundle on its back.
06:05Its wings begin to unfurl.
06:20Ten minutes later, the wings open.
06:24They'll never close again.
06:28Next, the huge muscles within its thorax must be exercised to prepare them for action.
06:42And it's away.
06:52Dragonflies, like mayflies, belong to the most ancient group of insects that flew over
06:58the land.
06:59And here in the museum in Harvard, there are fossils of them that are 150 million years
07:05old.
07:10They're almost identical with species that are still flying today.
07:14However, they're by no means the oldest.
07:20We know that there were other dragonflies even earlier, 225 million years ago, that
07:27were flying through the coal-mesher swamps.
07:31We don't have complete specimens of any of those, but there are some tantalizing and
07:37amazing fragments.
07:39Here's one.
07:54This marvelously preserved wing has very much the same pattern of veins supporting panels
08:01of membrane as living species.
08:05The thing that makes it different is its size.
08:10From base to tip, it measures 12 inches, 30 centimeters.
08:17Little imagination is needed to replace the membrane that must have been there.
08:21This insect must have had a wingspan as big as a seagull's.
08:30Vibrating these wings, preparing for flight, must have been a formidable business.
08:45A creature this size must have been at least ten times heavier than the largest insect
08:50flying today.
08:51How did it manage to get into the air?
08:54One suggestion is that in those far-off times, there was much more oxygen in the air, and
09:00that would have given the extra power needed to beat these huge wings.
09:06But it's a fair guess that this ancient pioneer of the skies flew with much the same technique
09:12as dragonflies do today.
09:21Living dragonflies can reach speeds of nearly 40 miles an hour and fly several miles in
09:26their search for new territory.
09:38They're all aerial hunters, relying on their supreme aeronautical skills to snatch their
09:44prey from the sky.
09:53Their great agility in the air comes from being able to beat each of their two pairs
09:58of wings quite independently.
10:06You can see clearly that they do this when the camera slows down the action 400 times.
10:14This one is coming into its perch.
10:18That control is essential to make all the tiny adjustments needed for an accurate pinpoint
10:24touchdown.
10:37All dragonflies, when they perch, hold their wings outstretched.
10:42But they have close relations to damselflies, and they perch with their wings closed above
10:47their backs.
10:49Mosquitoes stand little chance when damsels go hunting.
11:03But flight for damsels, as for dragonflies and mayflies, is primarily the means to find
11:08a mate and to breed, and to do that they, like the others, need water.
11:17Flight is itself an important element in their courtship.
11:21These blue males must first establish a territory for themselves above open water, and that
11:27involves aerial jousts that can last for hours.
11:37Mature females, whose wings in this species are not blue but golden brown, are attracted
11:42to those males who control good places for egg laying.
11:46But the males must nonetheless display the correct wing signals.
11:53This one, patrolling his territory, is using a special flight to flaunt his handsome wings,
11:59inviting females to join him.
12:06A female signals her willingness to consider doing so with a flick of her wings.
12:19So now he treats her to his full display.
12:30The female's tail-up posture is apparently a signal that declares that she's not yet
12:35sufficiently impressed.
12:44Now it seems he's got it right.
12:46Her tail is pointing downwards.
12:49He grabs the back of her neck with the claspers at the end of his abdomen.
12:57She brings her abdomen forward to reach a chamber under his thorax where he stores his
13:01sperm.
13:03His first action, though, is to scour out her genital tract to remove any sperm that
13:08might be there from a previous mating.
13:12Only when he's done that will he inject his own sperm.
13:21And now he must show her the best places in his territory for laying eggs.
13:31He flies up and down with his tail curled and lands on a suitable piece of vegetation.
13:41The female settles down to lay, cutting slits in the plant stems with her ovipositor and
13:48inserting an egg into each one.
13:51She may lay as many as 30.
13:55And all the time, the male keeps guard lest rival males should try to mate with her.
14:06In other damsel species, the males make sure that no other male can reach their partners
14:11by keeping hold of them throughout the whole process.
14:24The young that hatch from the eggs of these insects, the larvae, look very unlike their
14:29parents.
14:30This is a dragonfly larva, and it's in this form that dragonflies spend most of their
14:34lives.
14:37The larvae of both dragonfly and damselfly are savage predators.
14:41They'll even feed on their own kind if they get the chance.
14:54This particular larva has a very special problem.
14:58It's a cascade damsel, and it has to snatch prey that is swept past it by the rushing
15:04water.
15:08Cascade damsels are very rare and live around just a few Central American waterfalls, like
15:13this one in the mountains of Costa Rica.
15:25The adult male has to perform his courtship flight under very difficult conditions indeed.
15:49Somehow he's able to fly even when he's dripping wet.
15:53And he shows off to the females by actually flying through the cascades of water.
16:03To be a good breeding territory, the vertical rock surface has to be covered by just the
16:08right amount of water.
16:10Too deep and prey may be out of reach.
16:13Too shallow and the larvae could be picked off by birds.
16:19A female will only mate with a male if she approves of his choice of territory.
16:25And this one, it seems, does.
16:41This is it, and she carefully fixes her eggs to the rocks.
16:57But not all damsels need great areas of open water for breeding.
17:06In the rainforests of Central America, like this one here in Costa Rica, there's a damsel
17:11fly that has managed to break the link with open expanses of water like rivers and ponds.
17:17It's also one of the most spectacular members of the entire family.
17:26The helicopter damsel fly, the largest in the world, with a wingspan of up to 20 centimeters.
17:35The males tend to frequent sunlit patches where the females can see them easily, and
17:40they have a special lazy, flapping way of flying that is in itself an invitation.
17:59But although helicopter damsels can live away from rivers and streams, the females nonetheless
18:08require a little water in which to lay their eggs, and there is just enough in this little
18:15hollow here, and with luck, she'll come down.
18:34And into the water they go.
18:47But these eggs have watertight casings, so they can be laid in air.
18:52They are butterfly eggs.
18:54The link with water has been broken.
19:00Butterflies fly in a very different way from dragonflies.
19:04They overlap their two pairs of wings so that they flap as a single pair.
19:09They can't fly as fast or as aerobatically as dragonflies, but they nonetheless are tireless
19:15in their search for the particular food that will suit their young.
19:19And in the case of the cabbage white, that's cabbage.
19:31Now on the surface of this cabbage leaf, there's a patch of tiny little pillbox-shaped
19:37eggs, and when they hatch, the baby caterpillars will emerge and make an instant meal of the
19:44greenery.
19:49And they are already stirring.
19:54But the first dish on the menu is not vegetables.
20:01It's the shells of their own egg capsules, protein-rich and far too nourishing to be
20:07wasted.
20:09That first course, however, doesn't last long.
20:13Now for the main dish, cabbage leaves.
20:17When cabbage plants are damaged, their leaves release a smell, and that quite often attracts
20:23the attention of a rather different insect.
20:33It's a tiny wasp called cortesia.
20:37She too is trying to make sure that her young have food immediately available, but they
20:42like living flesh, so she injects her eggs into the butterflies' caterpillars.
20:53She does this with such surgical precision that her victims are not mortally injured,
20:59and they continue feeding as if nothing had happened to them.
21:15But now, much of what the caterpillars so laboriously gather goes to nourish the wasp
21:20grubs that are developing within them.
21:25As the caterpillars grow, they shed their skins.
21:29They do so five times, until ultimately they are 800 times heavier than they were when
21:35they first hatched.
21:37This fully grown caterpillar must now find shelter.
21:46A strand of silk trails behind it, silk with which it ties itself to a twig, and here,
21:52after a couple of days, it changes into a chrysalis.
22:06Those caterpillars that were injected by the cortesia wasp don't get that chance.
22:10The grubs within them are now emerging.
22:23They too spin silk, which hardens to form a cocoon beneath the caterpillar's empty skin.
22:33Inside, the wasp grubs are transforming themselves, and two weeks later, out come the adult wasps.
22:42A different future awaits the chrysalis.
23:05Within its shell and over a similar two weeks, the caterpillar's body has been broken down
23:10and reassembled, and now the adult is ready to emerge.
23:20Its wings, like those of a newly emerged dragonfly, need pumping up with liquid.
23:30The creature that was once an egg, then a caterpillar, then a chrysalis, has attained
23:42its final incarnation.
23:49So another generation of cabbage whites set off to find good places for their young.
23:57With their fragile-looking wings and apparently erratic flight, butterflies might not seem
24:03to be the most powerful of flyers, but in fact they are extremely accomplished aeronauts,
24:10and they can fly hundreds of miles, if necessary, to find the food they need.
24:24Some butterflies use the power of flight for another purpose, to escape bad weather.
24:31These lush subtropical valleys in southern Taiwan are warm and green all year round,
24:37and in winter they're filled by literally millions of butterflies.
24:53They've all come from the north of this great island, 500 miles away, for there the cold
24:58weather has killed off the plants on which they fed during the summer.
25:10In the mornings they take off from their roosts and head for the forest canopy to warm themselves
25:15in the rays of the rising sun.
25:19They have to conserve as much energy as they can, so instead of using their stores of fat
25:24to warm themselves, they absorb the sun's heat.
25:35There are four species of crow butterflies here, as well as two species of blue tiger
25:40butterflies, and all find enough food to sustain themselves in these warm and fertile valleys.
25:49Butterflies feed on liquid, nectar and the juices of rotting fruit, and to suck it up
25:53they have, instead of jaws, an extraordinarily long but extremely thin tube.
26:09In a newly emerged butterfly, this tube is in two pieces, for it is in fact a highly
26:14modified pair of mouthparts.
26:17Each half has its own muscles and nerve supply, so that the whole unit is fully movable and
26:23controllable.
26:28As the young butterfly prepares for adult life, these two sections are zipped together
26:33to form a tube like a miniature drinking straw.
26:36A special fluid cements the two halves together.
26:41The tube is largely made of a material called resilin, which, when distorted, springs back
26:46to its original shape, in this case a spiral like a watch spring.
26:51When the muscles within it contract, it straightens into a long probe that the butterfly can then
26:57insert deep into a flower.
27:14Butterflies and moths have the largest of all insect wings, and their great size means
27:19that they can be used very effectively as billboards on which to display patterns proclaiming
27:24the species of their owner.
27:27The patterns are produced by tiny scales that cover the wings like tiles on a roof.
27:33Some have a microscopic structure that refracts the light and gives the wing a brilliant iridescent
27:38shimmer.
27:41Others contain chemical pigments.
27:48With these lovely advertisements, a male butterfly displays to females and warns off rivals.
28:00Vivid patterns and bright colours are used to a much lesser degree by moths, for many
28:05are only active at night when colours, of course, are not easily seen.
28:14Moths also feed primarily on nectar, which they suck up in the same way as butterflies
28:19do.
28:21But one moth manages to tap a food source no butterfly has yet exploited.
28:28It comes from lantern bugs, which feed by drilling into the bark of a tree with their
28:34proboscis and sucking out the sap.
28:37This contains a little protein, which the bug wants, but a lot of sugar, most of which
28:42it doesn't want.
28:43So it squirts out the sweet excess.
28:46And to make sure that this doesn't attract ants that might attack it, it fires the droplets
28:51well away from the tree trunk with a tiny spring-loaded spatula at the end of its abdomen.
29:06One enterprising species of moth regularly sits behind the bug all night with the curled
29:12tip of its proboscis delicately placed in the stream of droplets.
29:30As sugar water accumulates, so the moth sucks it up.
29:44Most moths, however, feed by the rather more laborious method of flying from flower to
29:49flower.
29:50A few, the busiest, do so not only at night, but during the day as well.
29:55These are the hawk moths, and there are several species of them gathering nectar from this
29:59bud-near-bush in the south of France.
30:05This hawk moth can fly very fast indeed when it wants to, but it can also hover, as it's
30:11doing now, to sip nectar from each one of these small flowers.
30:18Beating its wings as fast as this, of course, takes a great deal of energy.
30:24So these hawk moths have to spend much of their day going from flower to flower, sipping
30:29the nectar, which is so rich in the carbohydrates they need to power their flight.
30:39They have huge forward-pointing lines that enable them to aim their proboscis with such
30:44accuracy that it slips into the exact center of each tiny flower.
30:51With so many minute flowers so closely bunched together, it would be easy for the moth to
30:56visit some twice, but that would waste energy, and if we mark each flower as the moth drinks
31:02from it, it's clear that the moth somehow or other never does this.
31:13Hummingbird hawk moths have no difficulty in hovering.
31:19Sea hawks, however, have heavier bodies, and they sometimes use their legs to help
31:23support themselves as they work.
31:32Their need to keep drinking is so pressing that a female will continue to do that, even
31:37when the male with whom she's mating seems to be trying to fly in the opposite direction.
31:47The Buddleia plant may be a particular favorite of hawk moths, but it is, of course, a foreigner
31:52introduced into our gardens from China in the 19th century.
31:57The hawk moth's original supplies of nectar came from the flowers of the meadows, and
32:02they still feed there, alongside many other insects.
32:06This is a carpenter bee.
32:08Bees also have two pairs of wings, but they're hooked together, so like those of butterflies,
32:14they operate as one.
32:20Bumblebees have particularly large and heavy bodies, and flight for them can be a real
32:25effort.
32:26That's particularly so in spring, when the mornings are cold, and queen bumblebees are
32:31just emerging from their winter sleep.
32:34It's only a few degrees above freezing, but a queen needs to get started early to look
32:40for food.
32:42The thick, furry hairs on her body help to conserve what heat she manages to generate.
32:49At the moment, she's only a few degrees warmer than the surrounding vegetation, as the thermal
32:54camera clearly shows.
32:56Her body is only marginally more pink than the blue leaves and moss around her.
33:03But she has a special way of warming up for flight.
33:09She can put her wings out of gear, so that, without moving them, she can rev up the wing
33:15muscles inside, and that raises the temperature within her thorax by 20 degrees centigrade
33:20or even more, as the expanding yellow image on the thermal camera indicates.
33:29Her body temperature is now over 30 degrees centigrade.
33:40At last, she has a chance of liftoff.
33:56She will now be able to visit the spring flowers while it's still too cold for others
34:01to do so.
34:18The long trumpets of the daffodils retain heat very well, and they're still warm even
34:23after their hot-bodied visitors have left.
34:34Flies, back in their distant evolutionary past, also had two pairs of wings, but their
34:39back pair have been reduced to simple knob-ended rods.
34:46These are particularly long on crane flies.
34:49They're part of the fly's flight instrumentation.
34:53Microscopic sensors on their upper and lower surfaces tell their owner about the air currents
34:57around its body, and so help in flight control.
35:01They start up even before take-off.
35:10Flies are such accomplished flyers that they can land upside down on a ceiling, or, in
35:15this case, the underside of a twig.
35:30Only when you slow down a fly's flight here by a hundred times can you fully appreciate
35:35what superb aerial control they have.
35:46Some species, like these long-legged flies, flaunt their wings in courtship just as damselflies
35:52do.
36:03These danceflies are voracious hunters, and it's particularly important for them that
36:08they perform their dance correctly.
36:10If one doesn't get it right, its partner might well eat it.
36:29This performance, however, seems to have been up to standard.
36:56For hoverflies, arguably the most accomplished of all insect aviators, immaculate aerial
37:17control is what makes a male attractive to a female.
37:23A male lays claim to a mating territory by trying to stay in exactly the same position
37:28in space for as long as possible.
37:31That's not easy when there are others all around you trying to do precisely the same
37:35thing.
37:36It might seem that he's absolutely motionless, but in fact he's having to make continual
37:44changes to adjust for slight currents in the air.
37:48It's an amazing piece of acrobatics, far better than anything that we can do in a helicopter.
37:57And it's all done in order to impress the female, to show her that he is superb at holding
38:06his territory.
38:13Trying to chase away rivals that come too close is an exhausting business.
38:18And when you're trying to maintain your hold on a particular point in mid-air, even a small
38:22midge has to be chased away.
38:33After a morning spent doing this, a male hoverfly may have lost as much as a third of his bodyweight.
38:39It's no wonder that he takes a break at midday in order to rest and refuel.
38:45He dabs up nectar with mouthparts that are shaped like a pad.
38:59Having refilled his fuel tank, the male returns to his territory for the afternoon session
39:05of hovering, in the hope of attracting yet another female and mating with her.
39:15Once again, with his superb eyesight, he's ready to spot anything that might whiz by
39:21him at high speed that could be a female, and I might just be able to fool him with
39:26a pea-shooter.
39:49Although there may seem to be an extraordinarily large number of different flies in the world,
40:14it's actually the beetles that are the most varied of all insect groups.
40:19There are 300,000 species of them.
40:23Most find their food by crawling and burrowing on the ground, and to prevent their wings
40:27from being damaged in the process, they've turned the front pair into protective shields.
40:33Some, like weevils, keep their wing covers permanently closed and before take-off push
40:39their functional wings out of special slits.
40:44Ladybirds, like most other beetles, raise their wing covers and hold them clear of the
40:49hind wings throughout their flight.
40:51The result could hardly be called aerodynamic, and consequently their flight is rather lumbering.
41:02Blister beetles are scarcely any better.
41:12When a flight is over, the hind wings have to be packed away beneath the covers, a process
41:16that can be so complex that it demands all the skills of a Japanese master of origami.
41:40With flight playing a relatively small part in their lives, many beetles have grown very
41:45large.
41:46This one, the titan beetle that lives in the forests of the Amazon, is almost certainly
41:51the biggest of all insects.
41:55I have to handle him with considerable care because those huge mandibles at the front
42:03are powerful enough, it's said, to be able to cut straight through a pencil.
42:09He can fly, but he can't get into the air from the ground.
42:13He's too heavy to do that, so he has to climb trees and launch himself into the air that
42:19way, and that's why he's got such powerful legs armed with sharp claws.
42:25The titan is now known to be the biggest of all beetles.
42:30The champion is seven inches long from the tip of the mandibles to the tip of his abdomen.
42:36The larva of this great monster has not yet been found, but it must be at least twice
42:42as big as the beetle, a really huge grub.
42:48Beetles and many other insects spend so much of their lives as flightless larvae that it
42:52would be more accurate to think of them as creatures of the earth rather than the sky.
42:58Flight for them, as it is for the mayflies, is a relatively brief episode at the end of
43:02their lives.
43:04These cicadas in the eastern United States spend 17 whole years below ground, sucking
43:10sap from tree roots, and then, within a few days, a whole population emerges.
43:32There may be millions of them in a single acre of land.
43:43They clamber up the trees, whose roots have provided them with sap for all of those seventeen
43:49years.
44:08And here they change into their adult costume.
44:36Now they have the wings they need to search for a partner.
44:44Empty larval cases cover the tree trunks and the ground beneath.
44:53And above, in the branches, the millions have started to sing.
44:58The noise is ear-splitting.
45:17After seventeen years of living underground, the cicadas are now approaching the climax
45:23of their lives.
45:25And for the males, that means this.
45:34The call is his way of attracting a female.
45:45The females reply with a quite different sound, a click made by flicking her wings.
45:56So that's what the males are listening out for.
46:00I can imitate the female's wing-flip with a snap of my fingers, and that causes them
46:07to follow me anywhere because they're so determined to find a female.
46:27Now, can I bring you back?
46:34How about coming this way?
46:45Oh, the noise is awful.
46:48Come this way.
46:50Come on.
46:51Yes, I can hear you.
46:54Oh, quite right.
47:00At last, a male finds his partner, and as he does so, his call alters.
47:08He's indicating to her that, after seventeen years, the time has come to get down to business.
47:31How do these cicadas all emerge simultaneously after seventeen long years?
47:38Well, we know that they can appreciate changes in the contents of tree sap, so they're able
47:45to detect the passing of a year.
47:48But how do they count up to seventeen?
47:51We have no idea.
47:53But even if we did, this surely would remain one of the most astonishing, amazing events
47:59in the insect world, and it'll all be over in a couple of weeks for another seventeen years.