- It is summertime, and the air is buzzing with the sound
of flying bugs. Others are crawling in the undergrowth, dangling by silky
threads or hanging out beneath stones. Some dare to venture on to our prized
roses or - even worse - become uninvited guests in our kitchens, where
the final ignominy awaits them under a rolled-up newspaper.
-
- There are some things we cannot tolerate, and the creepy-crawly
is one of them. Go to any garden centre and marvel at the range of sprays,
powders and poisons that can be deployed against the common enemy, whether
it be a six-legged aphid or a one-footed snail. Few of us mourn when these
diminutive annoyances get zapped by the latest addition to the chemical
arsenal. We support campaigns to save the panda, the whale or the tiger,
but whoever heard of anyone trying to save the weevil?
-
- Yet saving the insects and other arthropods - animals
with external skeletons - is precisely what we should be doing. This class
of life is more diverse than any other on the planet, and without them
we humans would simply not exist. Insects are not just the embodiment of
life on earth; they are to a great extent the reason why life is so rich,
and so beautiful. Without insects, we would have no flowers and no fruit.
As well as pollinators, insects are nature's refuse collectors: without
them, dead plants and animals would not be recycled and the land would
begin to drown in waste matter. If insects were to disappear tomorrow,
forget worrying about your pension - you wouldn't need it.
-
- But try telling the public this. The Royal Entomological
Society is having a stab at it by organising the first National Insect
Week, which began yesterday at the Natural History Museum in London.
-
- Perhaps the most eloquent praise for insects comes from
the veteran ant-watcher Edward O Wilson, the Harvard entomologist and Pulitzer
prize winner, in his 1992 book The Diversity of Life: "So important
are insects and land-dwelling arthropods that if all were to disappear,
humanity would probably not last more than a few months. Most of the amphibians,
reptiles, birds and mammals would crash to extinction about the same time.
Next would go the bulk of the flowering plants and with them the physical
structure of most forests and other terrestrial habitats of the world.
The land surface would literally rot.
-
- "As dead vegetation piled up and dried out, closing
the channels of the nutrient cycles, other complex forms of vegetation
would die off, and with them all but a few remnants of the land vertebrates.
The tree-living fungi, after enjoying a population explosion of stupendous
proportions, would decline precipitously, and most species would perish.
The land would return to approximately its condition in early Palaeozoic
times, covered by mats of recumbent wind-pollinated vegetation, sprinkled
with clumps of small trees and bushes here and there, largely devoid of
animal life."
-
- Life without insects is a bleak prospect, so why do we
persist in treating them so badly? Apart from butterflies, ladybirds and
bumble bees, insects seem to be universally despised, looked on as ugly,
dirty, disease-ridden and generally beyond the pale.
-
- Part of the problem is aesthetics. Something with six
or eight legs is just not cuddly enough for our photogenically obsessed
society. It has taken Sir David Attenborough years to persuade the BBC
to do something to address the public's entomological ignorance. He has
finally succeeded, and is now in the middle of filming Life in the Undergrowth,
his new series on invertebrates, to be shown in 2006.
-
- "We go on making films about lions and wildebeest,"
Sir David once told me while gazing into the back garden of his London
home, "when there are thousands of unbelievably dramatic stories,
totally unknown and untouched, just out there." To put it another
way, there is more sex and violence in the torrid heat of a compost heap
than there is on Channel Five.
-
- To understand the environmental significance of insects,
it is necessary to know their story. They first appeared about 400 million
years ago as the dominant form of life on land, long before the first animals
with backbones crawled out of the sea, and about 380 million years before
the first human-like apes began to walk on two legs.
-
- Their basic body plan has proved an unbeatable blueprint
for success. Insects typically consist of three segments - a head, a thorax
and an abdomen - propped on six legs with a set of wings. They go in for
a phenomenon called metamorphosis, which allows them to transform from
one type of organism - a leaf-eating caterpillar, say - into another, such
as a sexually mature butterfly that sips nectar for high-octane fuel. This
allows one species to exploit two quite different diets and habitats.
-
- Fortunately for human beings, the size of insects is
constrained by their external skeleton. They breathe through holes in their
waxy cuticle, which restricts the amount of oxygen that can be diffused
to their tissues. This severely limits how large they can be - which is
just as well, because if ants could grow even as big as rats, kitchen invasions
from the garden would take on a whole new meaning.
-
- Perhaps the most amazing thing about insects is their
diversity. Metamorphosis, their small size and their mobility have allowed
them to exploit just about every habitat on land and fresh water. It is
reckoned that there are about 900,000 species of insect formally described
by science - more than all other known animals, plants, fungi and bacteria
combined.
-
- But these are only the known insects. Scientists can
only guess at the ones that have yet to be discovered. Some entomologists
suggest that there are between three million and six million insects and
arthropods still unnamed. Others think the total could be as high as 30
million.
-
- Such abundance is staggering. Wilson says: "Entomologists
are often asked whether insects will take over if the human race extinguishes
itself. This is an example of a wrong question inviting an irrelevant answer:
insects have already taken over."
-
- By far the biggest group of insects is the beetles, with
something like 330,000 named species - more than all non-insect animals
together. Why beetles should be so diverse
-
- remains something of a mystery. Indeed, the great British
biologist and atheist JBS Haldane once said, when asked whether studying
biology had taught him anything about the Creator: "I'm really not
sure, except that He must be inordinately fond of beetles."
-
- More recently, the diversity of insects, and in particular
beetles, has been linked with the wider diversity of life on earth, particularly
the flowering plants. Biologists believe that a struggle between insects
and the plants they live on has led to them both becoming more diverse
by a process called co-evolution, when the evolution of one species drives
the evo- lution of another.
-
- A good example of this is an orchid called Angraecum
sesquipedale, found on the island of Madagascar. The unusual feature of
this orchid is that its pale white flower is shaped into a narrow, 16-inch
deep shaft, at the bottom of which nestles a few drops of nectar. No known
insect at the time this orchid was first discovered would have been able
to reach this nectar, which gave rise to the question: why was it there?
-
- Charles Darwin, who was fascinated with flowers and the
insects that pollinate them, first came across this orchid in the middle
of the 19th century and predicted that there would be a species of moth
with a tongue long enough to reach down to the nectar. Sure enough, in
1903, after Darwin had died, entomologists found a moth on Madagascar that
could unfurl a 16-inch tongue that was perfectly adapted to feed on the
orchid's deep-seated nectar. They named it Xanthopan morgani praedicta
- praedicta in honour of Darwin's prediction.
-
- The point about the tale of the moth and the orchid is
that it shows how each co-evolved for mutual advantage - of pollinating
the flower in the case of the orchid, and of gaining the nectar in the
case of the moth. Other cases of more cut-throat co-evolution between plants
and insects, where one is trying to out-do the other, are now thought to
have driven evolution to produce today's breathtaking biodiversity.
-
- Take, for example, the diversity of the beetles. Why,
or how, could it have arisen? Brian Farrell, a Harvard entomologist, conducted
a series of studies in the 1990s to try to answer the question. His findings
clearly point to co-evolution, this time the result of a 300-million-year
war between beetles and the plants they want to eat.
-
- Plants have evolved many mechanisms to prevent them being
eaten by insects, notably physical defences, such as spines, and chemical
defences, such as toxins. The most primitive beetles - our friends the
weevils - were not primarily plant-eaters but fed on fungus and smaller
insects. But, about 230 million years ago, a new group of beetle moved
to a more exclusive diet of plants. As a result, they soon diversified
into many different species - leaving the weevils stuck in an evolutionary
rut.
-
- Later, when flowering plants first evolved about 120
million years ago, these plant-eating beetles diversified even further
than their cousins who stayed behind eating non-flowering plants such as
ferns. Farrell had shown that diversity went hand in hand with co-evolution.
As insects invented new ways to devour flowering plants, so flowering plants
invented new ways to keep them at bay. This helped to generate new species
of flowers, demonstrating that diversity led to more diversity.
-
- It is perhaps a salutary lesson that the ugliest organisms
we can imagine - insects - have helped to shape and give us the most beautiful
things in nature. But the tiny creatures can be credited also with shaping
history: the midge drove English soldiers to distraction in the Scottish
Highlands, and the mosquito helped to turn West Africa's forests into a
white man's graveyard.
-
- Insects carry disease, and they have proved a formidable
foe by spreading some of the most debilitating infections known to man,
from malaria to Chagas disease. By pollinating our orchards and crops they
have created plenty, but they have also wreaked havoc by eating our food
before and after it has been harvested.
-
- For as long as people have farmed the land, insects have
been the greatest pests. And for as long as we have sprayed pesticides,
as the Sumerians did 4,700 years ago when they sprinkled sulphur on their
fields, insects have fought back - just as they had devised ways of co-evolving
with a plant's natural toxins over many millions of years.
-
- For many years, the battle went the insects' way. Now,
with modern pesticides and GM crops, insects find survival increasingly
difficult. Intensive agriculture in Britain has made farming more efficient,
leaving less food for insects and helping to starve out the more photogenic
creatures, such as skylarks, that depend on them.
-
- A study by Jeremy Thomas of the Centre for Ecology and
Hydrology in Dorset has found that butterflies have suffered greater declines
in Britain in the past 40 years than either birds or plants. The findings
have demonstrated that insects are not immune to global mass extinction.
-
- This is why we must celebrate our six-legged friends
and not swat them whenever we can. As EO Wilson says, we must give respect
where respect is due. We humans are newcomers among the ancient six-legged
masses, and we have only a tenuous grip on the planet. "Insects can
thrive without us," Wilson says, "but we and most other land
organisms would perish without them." Small wonders: the amazing world
of insects
-
- * About one billion billion insects are alive today,
weighing considerably more than the mass of all humanity
-
- * There are about 900,000 known insect species, and millions
more yet to be discovered
-
- * They have dominated the land for more than 400 million
years
-
- * Scientists estimate that more than 160 species of beetle
can live in the canopy of a single specimen of one species of tropical
rainforest tree
-
- * The biggest insects include the stick insects of Borneo,
which grow up to 14 inches long, and the long-horned beetles of South America,
whose bodies are six inches long
-
- * The longest-living insect is probably the cicada, which
lives underground as a sap-sucking juvenile until it emerges to breed at
the end of a 17-year life-cycle
-
- * Cockroaches can survive a blast of radiation strong
enough to kill a man outright
-
- © 2004 Independent Digital (UK) Ltd http://news.independent.co.uk/world/science_technology/story.jsp?story=531243
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