Dry Storeroom No. 1 (35 page)

The systematic result is that the old order must be revised in the most literal sense: termites become social cockroaches and must be classified together with these large insects in the cockroach Order Blattodea. Goodbye Isoptera. This proves that the hierarchy of a classification is always just provisional, and dependent on the state of knowledge. Even an Order can vanish as evolutionary history is better understood. There had actually been hints of the close relationship between
Cryptocercus
and termites before the new evidence came along: they share some very distinctive tiny organisms in their gut “flora.” Science is often like this: an idea has been around for a while before new evidence suddenly pushes it forwards. And then researchers tend to think: maybe this example is not so surprising after all. The cockroaches are persistence incarnate; they have been around since the Carboniferous period, and will doubtless outlast mammals, and indeed just about everything else on our vulnerable planet. If there were a nuclear disaster of universal proportions, or global warming cooked us all, I can imagine cockroaches crawling out of cracks in the earth in the aftermath to clean up the mess. Nobody likes them much, but they are probably going to survive our passing. And if vegetation also survives in any form in the future, their relatives the termites will be there, too, demonstrating the strength of numbers and a prolific society—mindless but almost indestructible.

Some insects are particularly useful in monitoring the climatic changes that may yet secure the dominion of the cockroach. Steve Brookes works on chironomid midges. If you have seen a vaguely irritating black fuzz of tiny insects around the edge of a pond, the chances are that it will be composed of a mass of chironomids. Unlike the biting midges that drive one mad in Scotland in the summer, chironomids don’t need to take a nip of flesh to reach maturity. Their larvae feed in ponds on small organisms like diatoms described previously. As they grow, they moult. Their cast headshields are readily preserved in the soft sediments that accumulate in the bottom of freshwater lakes, becoming effectively tiny fossils. Since different chironomid species live in different climatic regimes, they change in harmony with changes in climate: their little fossils can provide a good proxy for fluctuations in temperature. Because they are so small, they can be recovered in significant numbers from the tiniest sediment samples. Where deposition of sediment in lakes has been continuous over thousands of years, the chironomid fossils give us an historical narrative of climate change. This can be matched to independent evidence derived from other continuous historical narratives, such as those provided by the Greenland ice cores, where variations in oxygen isotope ratios provide a measure of past temperatures, or the sediments of the deep sea, where the tiny shells of fossil foraminiferans perform the same function. Naturally, a standard is needed to calibrate a given fossil assemblage in terms of the ambient temperature of the time. Steve Brookes and his colleagues made a profile of chironomid species’ abundance in July running from the Arctic island of Spitsbergen, 80 degrees north, to southern Norway, 58 degrees north, and ranging in altitude from sea level to 1,600 metres. With the optimum requirements of any species so determined, these scientists were in a position to interpret cores through ancient sediments. The sampling can be down to a millimetre or two, representing time slicing of the order of a decade, applied over the last fifteen thousand years or so. There proved to be a large number of lakes that provided appropriate core samples for analysis. Thanks to their new methods, the oscillations of the climate through warming or cooling could be monitored in the shifts of populations of the tiny midge fossils from the sedimentary samples; as the surrounding environment fluctuated, so did the dominant species of these tiny creatures. Sometimes the small size of insects is their greatest virtue. Mammoths and cave bears cannot be used with such precision. And now with the attention of the world focussed on climate change, understanding what has happened in prehistory has never been more important, in our attempts to sift out man-made from natural climate fluctuations. Study of the smallest things can sometimes attack the biggest questions.

A microscopic slide of a midge head (
Heterotrissocladius grimshawi
)—an example of a chironomid used for studies of climate change

When celebrating the sheer exuberance of the insects the beetles always come to mind. I have mentioned that estimating the number of insect species in the world—most of them still unnamed—has been the cause of much disagreement. The best I can do is to offer the opinion of the International Entomological Congress held in Brazil in 2000, when a symposium on the subject finished up with a questionnaire: the majority of entomologists believe that there may be something like eight to fifteen million species on our planet. There are an estimated twenty-eight million insect
specimens
in the Natural History Museum, including about a quarter of a million type specimens. The largest component of these vast collections is the beetles, which comprise something like 30–40 per cent of the insects. Peering into a drawer of pinned beetles is like looking down at an immense miniature army, all shinily decked out in their battle gear. The footsoldiers are black and small, seemingly endless battalions of them, but here is a rank of larger iridescent green officers, and there a battery of rhinoceros beetles equipped with pikes, lances and halberds. A great number of beetle species remains to be discovered—no two coleopterists agree exactly on the figure. The 430,000 or so named species seem to be quite enough to be getting along with. Beetle specialists tend to be very specialized. They are likely to study just one family (or even a genus), not unreasonably saying that this is already a lifetime’s work. The world belongs to beetles, which can live anywhere and eat anything. The key innovation during their evolution was turning one of the usual pairs of insect wings into hard covers, or elytra, which are used to cover up the other, flying pair. They can wrap their wings away until needed. Beetles get under logs and down into the soil and into dung balls and all kinds of tough places because, as my coleopterist colleague Peter Hammond puts it, they are “crunchy.” I prefer to stick with my military analogy and think of them as armour plated. Anyone who has squeezed a ladybird and seen it walk away a few seconds later quite unfazed will know what I mean. And then the wings can be unwrapped and, delicate as a thistle seed, the little fellow flies away. They can feed happily on wood or pollen or mushrooms or oil spills, or whatever, and then fly to meet their mates when they need to. Some of the weevils don’t even need water—they can make it from the wood or grain they eat.

A parade of beetles: just a sample of the most biodiverse group of organisms

One of the largest and most distinctive beetles: the rhinoceros beetle

I might say that the only resemblance between Peter Hammond and his objects of study is his beetling brow. Otherwise, he is classically handsome, smokes a pipe, and has the splendid chisel jaw of a leading man in a 1950s detective drama. He is devoted to a family of beetles called staphylinids, better known as rove beetles. They are active, flexible beetles with very short elytra—under which the other pair of wings is folded. If you turn over a rotten log, the chances are a dark-coloured “staph” will run away from the light in a few seconds. This family alone has forty thousand described species, and Peter thinks that there may be half a million different kinds of them. The species are often told apart by details of the genitalia, as well as by more obvious things like colour and ornament; Peter’s colleague Jim Bacchus referred to monographs identifying these beetles as “prickture books.” A pun might make the task of getting to know tens of thousands of unnamed species a little less intimidating.

I wonder how entomologists cope with facing this Mount Everest of unnamed species. Some tackle the mountain by the north face, head on, by trying to describe and name as many species as a life allows. An American entomologist called Alexander may hold the record; he worked on the crane flies, Tipulidae, and is said to have named some twenty thousand species, using millions of words to systematize their endless variety. Noble though these endeavours are, they are doomed to failure; there is just too much to do. In 1971–72 four young men from the Museum—Mick Day, David Hollis, Dick Vane-Wright and Peter Hammond—set out on a major expedition to South-west Africa, to collect as much insect material as they could in five months. They adapted an army truck as a field laboratory. They managed to purchase the old truck for the mighty sum of £300; then they grafted an army fire engine on to the front so that there was room for them all in the “cab.” Dick Vane-Wright proved to be as good a carpenter as he was a lepidopterist and fitted out the laboratory in fine style; Mick Day turned out to be that most important person on any expedition, a talented field mechanic. Peter Hammond says he wasn’t good at anything so he acted as a porter. The whole expedition cost a mere £3,000, including the vehicle, a sum that now seems laughable even allowing for inflation. During the trek across Namibia, Botswana and southern Angola the team collected millions of specimens—simply too much to deal with, and much of it still hasn’t been. Then there was a project in Sulawesi organized by the Royal Entomological Society in 1985 to provide the first, and only, complete inventory of the insects of a tropical rainforest. Up to a hundred entomologists were involved. The canopies of trees were “fogged” with insecticide to bring down their hidden denizens. Rotting vegetation and soil were sampled—in fact every thing that could be sampled was sampled. Peter Hammond reckons he personally examined a million beetle specimens under his microscope. The idea was not to name everything, but to establish just how many species there were, to get some estimate of tropical biodiversity. The relevant specialist might be able to identify a genus, for example, and assign a dozen species to it, even if many of them were new to science. The exercise proved both that diversity was higher than anyone expected and that there was a host of unknown species living particularly in the lower canopy and in the litter layer.