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The Bug Picture

  • Written by  George McGavin
  • Published in Opinions
‘At what point does the web of life become so frayed that is starts to disintegrate?’ ‘At what point does the web of life become so frayed that is starts to disintegrate?’ Lara Zanarini
27 Aug
How many other species do we share our planet with? The truth is we don’t have the foggiest idea

Some early guesses of 30 million or even 100 million have been replaced in the last few years with more reliable estimates of somewhere between five to ten million species. But despite this massive uncertainty there is one thing which is indisputable – the vast majority of Earth’s inhabitants (~65 per cent) are invertebrate and most of those are insects.

It is therefore not very surprising that these creatures have a pre-eminent impact on the functioning of global ecosystems. Creatures like us – and I don’t just mean primates, but all back-boned animals from aardvarks to zebras and axolotls to zorrillas (a striped polecat in case you were wondering) make up less than three per cent of all species.

Yet it is these very animals that most people hold dear. I use a slide in my lectures which has images of all sorts of insects along with one face-on image of a female slender loris with a baby on its back. No prizes for guessing the first, and probably the only, thing audiences look at. It seems we can’t help ourselves. Attractive they may be, but in the great ecological scheme of things, they are pretty useless. If you really want to understand the world around you – you need to get down to some serious entomologising.

At what point does the web of life become so frayed that is starts to disintegrate?

Pollination is perhaps one of the most essential symbioses ever to have evolved. This plant-insect version of ‘I’ll scratch your back if you scratch mine’ has been around for 100 million years and it has given the world a rich diversity, and not just of flowering plants. Twenty thousand species of bee are responsible for the continued survival of the angiosperms, which includes a very long list of fruit and vegetables from pumpkins, plums and peas to cherries, cucumbers and cocoa.

What about herbivory and carnivory? Ecology really doesn’t get much more basic than this. The light energy from the sun is converted to chemical energy and the plants – the producers – that carry out this astonishing transformation are fed on by primary consumers – the herbivores. They in turn are eaten by secondary consumers – the carnivores.

But what does these jobs? It may come as a surprise to many that all the heaving, snorting herds of grazing ungulates are entirely ‘out-munched’, perhaps by a factor of ten to one, by myriads of tiny mandibles. What about the meat-eaters? Again, insects consume many times more animal flesh than all vertebrate carnivores
put together and ants alone are the major carnivorous species in any habitat you could mention.

If this sounds implausible, consider that although insects are individually small, there are an awful lot of them – an estimated ten million, million, million (1019) with an impressively large biomass. Insects are also the major food source for countless species. Many trillions of insects a year are eaten by birds and bats and a whole bestiary of other furry and feathery creatures. Space prevents me from extolling the role of insects in global decomposition and nutrient recycling.

But there is a problem looming – the first effects of which we are already feeling. Almost every study that has been done to date points to a steady decline in insect species richness and abundance. The loss of natural habitat and the prodigious amounts of pesticides used in agriculture are taking their toll. The decreases seen in well-studied insect groups such as bees and butterflies are surely taking place in many other groups as well. At what point does the web of life become so frayed that it starts to disintegrate? We may find out sooner rather than later.

Our planet could lose more than half of all its living species in the time it takes for a tiny acorn to become a veteran oak tree

It is thought that the world’s tropical forests hold more than half of all extant species. If these complex habitats are being felled and degraded at even the slowest rate that has been suggested, it will still only be a matter of a few hundred years before they are lost. It is therefore an inescapable conclusion that our planet could lose more than half of all its living species in the time it takes for a tiny acorn to become a veteran oak tree.

Should we be worried? Well, it all depends on your point of view. Ninety-nine per cent of all species that have ever lived on Earth are extinct and it was the occurrence of numerous extinction events that paved the way for the appearance of those creatures that led to human beings. The difference is that now we know enough to do something that might just prolong our own survival.

There’s no doubt about it – we are the most intelligent and capable species yet to evolve on Earth. In a very short time since our appearance we covered the entire globe, establishing colonies wherever it was possible to survive. A few of us have walked on the surface of the moon and visited the deepest abysses of the oceans. We spend vast sums of money to probe the very make-up of matter and remotely examine other parts of our solar system. We want to understand the science of everything from the infinitesimally small to the astronomically large. This truly is ‘big’ science and of course it’s expensive. But do we have to do it right now? What about understanding the biosphere a bit better? Perhaps what we actually need is bit more ‘bug’ science.

George McGavin is an entomologist and zoologist, and a presenter of various wildlife programmes for the BBC

This was published in the September 2016 edition of Geographical magazine.

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