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When a Scorpion Meets a Scorpion

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The invention of the microscope revealed wonders to the world, and permitted Jonathan Swift to quip:

So, naturalists observe, a flea
Hath smaller fleas that on him prey
And these have smaller still to bite ‘em
And so proceed ad infinitum.

By the late twentieth century fascination with the minuscule had begun to pall, and now it takes an exceptional book indeed to reawaken our interest. Thankfully, in David Attenborough’s Life in the Undergrowth, Piotr Naskrecki’s The Smaller Majority, and Jeffrey Lockwood’s Locust we find three works that do so.

Life in the Undergrowth is Attenborough’s tribute to the terrestrial invertebrates. They are, he says, a group of creatures that make life possible for us—whether as scavengers, aerators of soil, or agents of pollination, to name only three of their functions—but because they are small we largely ignore them. As he succinctly puts it, “We are greatly prejudiced by our size.” This is the latest in a series of projects combining television and print in a unique manner that has become Sir David’s métier. His investigations encompass disciplines as diverse as paleontology, botany, zoology, and ethnography; and each is similar in scope to a doctoral dissertation. While most of us think of Attenborough principally as a television presenter, he is also one of the greatest ecologists, synthesizers of evolutionary science, and teachers of our age.

In each of his investigations Attenborough takes multiple parts, including instigator, researcher, scriptwriter, presenter, and author of a book summing up his inquiries. Because of the highly sophisticated recording equipment and laboratories at his disposal, and because he and his team spend long months in the field, fundamental discoveries have been made during the course of this work. Life in the Undergrowth was no exception, with Attenborough’s sound recordist discovering that certain caterpillars create sounds that charm ants into caring for them.

The land-dwelling invertebrates (animals without backbones) are so diverse that they make up most of the species on Earth. This makes producing an overview of them particularly challenging. Attenborough adopts an evolutionary approach, and as he tells his tale he picks out species that take a particular adaptation or behavior to an extreme. This allows him to capture the general direction of the group’s evolution as well as its breadth of diversity, without drowning us in detail.

Life in the Undergrowth commences with the descendants of the first creatures to clamber out of the water and onto land—the scorpions and their relatives. They made the transition some 400 million years ago, long before plants or our ancestors left the oceans. If you have never thought of scorpions as remarkable, Attenborough advises that you try to pick one up, perhaps with a pair of very long forceps. Whichever method you use it will not be easy, for scorpions possess advance warning systems that sense where you are and what you are doing. Their six pairs of eyes are strategically positioned so as to leave no blind spot, and while lacking sharp focus they are capable of detecting the tiniest variations in brightness—and thus movement. Yet they cannot be dazzled because each one has its own built-in “sunglasses,” composed of pigment granules, which cover the lens as light increases.

Before it sees you a scorpion will either have “heard” you through the minute hairs on its claws, or detected your advance through a slit-shaped organ on the upper part of each leg, which is so sensitive to vibration that it can pinpoint the footfall of a beetle a yard away. Or perhaps it will have detected you with its pectines. These comb-like organs have no parallel among other living creatures. They are packed with nerve endings and are probably capable of smelling or tasting minute traces of chemical compounds in the ground over which the scorpion passes.

When a male scorpion meets a female scorpion, his mind is very much on the ground under his feet. You can tell this from his pectines, which scan the earth while he shakes his body back and forth. He then approaches the female and stings her on the soft flesh in the joints of a pincer. This seems to relax her, allowing him to grasp her claw in claw, bring her face to face, and begin a scorpion waltz. In the laboratory, scorpion pairs have waltzed for two days. But in nature half an hour or so seems to suffice, with the dance terminating when the male locates a really choice piece of ground (the long laboratory waltz may occur because the male cannot find the right type of ground). Soil texture is important in scorpion sex because instead of a penis males have a detachable spike which must be firmly implanted in the ground if insemination is to occur. Once the spike is in place the male maneuvers his partner so that her genitals are atop it. As the spike bends under her weight two tiny valves open, through which the sperm is released.

It’s difficult for human beings to see scorpions at night, but it’s easy for scorpions to see other scorpions. That is because scorpions produce bright green fluorescent light, which is clearly visible to them but invisible to the human eye. These superb adaptations have been honed by 400 million years of evolutionary experience during which countless billions of individual scorpions with blind spots, less sensitive pectines, or poor fluorescence have been weeded out, until finally we are left with the seemingly perfect, yet utterly alien, creatures here described.

If you imagine that worms are any less intriguing than scorpions, Attenborough has surprises for you. The largest worms on earth inhabit an area of about eleven square miles in Gippsland in southern Australia. It’s difficult to establish just how long these creatures are, for they keep changing shape from (relatively) short and squat to long spaghetti-like strands. Attenborough settles on a meter; but their changing shapes are hardly their most surprising attribute, for the giant Gippsland earthworm is more often heard than seen. As these subterranean creatures move about in their tunnels they produce sounds like water going down a plughole, or more occasionally like a toilet being flushed. The town of Poowong in West Gippsland supposedly derives its name from an aboriginal word describing the sound of the worms as they shift about: Pwwwong!

Every year or so the giant Gippsland earthworm deposits a case holding a fertilized egg in the wall of its burrow. It’s about the shape and size of a cocktail sausage, and if you hold it up to the light, inside you will see a single baby worm. By the time it hatches twelve months later it will already be eight inches long—larger than a normal earthworm. Such slow reproduction indicates that the worms are long-lived. They may be as old as you or I.

Biologists were recently asked to relocate a colony of giant Gippsland earthworms that lay in the path of a new highway. Each worm had to be painstakingly excavated and released into a new burrow. To their surprise the researchers discovered that the worms had different personalities: some were placid, others agitated at the intrusion; one was actually described as “aggressive.”* No one seems to know why.

Attenborough raises an analogous question of insect personalities when he discusses the bolas spider:

When we were filming…we had in front of us a line of bottles, each of which supported a spray of leafy twigs in which crouched a small bolas spider. These tiny creatures catch moths by whirling a filament of silk with a sticky blob at the end, whenever one came near them. Kevin Fleay, the cameraman, had been working with them for nearly a week and he introduced them to me individually. This one, he told me, was very shy. The slightest vibration made her draw up her legs and stay motionless no matter how near a moth came. That one reacted in the same way if the light was too bright. A third didn’t seem to mind how much light was shone on her but on the other hand she was unpredictable. Sometimes she would hunt and sometimes not. But the one at the end of the line, no matter how much she had eaten, or how much light shone on her, would whirl her bolas whenever a moth came anywhere near and usually caught her prey. These tiny creatures half the size of my fingernail each had individual characters.

The fact that invertebrates have characters seemingly similar in their fundamentals to those possessed by ourselves is a theme to which Attenborough returns repeatedly, and as he does so the gulf between the least and greatest of living things diminishes. But Life in the Undergrowth offers another revelation that seems to close that gap further. At a time when our rat-sized ancestors were still cowering in the shadows of the dinosaurs it is probable that certain insects had already created cities, farms, and skyscrapers, and today their descendants have become highly sophisticated indeed.

Among the most thought-provoking of such creatures are the ranchers. These ants carefully tend herds of sap-sucking aphids, tiny pear-shaped insects, which they milk for a sugary substance that makes good ant food. Just like human farmers, the ants ensure that their herds get the best possible forage. They do this by driving their aphids to parts of the plant that are rich in sap, and when the aphids produce young (which are miniature versions of the adults), the ants carry them to fresh pastures. Ant shepherds drive off aphid predators such as ladybirds, and in bad weather build shelters of leaf particles and soil to protect their livestock. They have even been observed marking their herds with a substance specific to one ant colony; it resembles our branding of livestock, Attenborough says. But most astonishingly, the ants have discovered how to interfere with the reproduction of their herds so as to maximize production; just as we castrate calves, so the ants feed their aphids a fluid which prevents them from reaching sexual maturity.

Other ants and some termites have become farmers. They create great underground factory-farms of enormous complexity, within which they maintain conditions that promote the growth of nutritious fungi. The Bible commands us to look to the ant, but few would think to find there industries of such complexity and sophistication. The greatest of Earth’s architects and builders are the termites. These distant relatives of the cockroach build cities whose spires tower far higher above their inhabitants’ heads, relative to their size, than do our tallest skyscrapers. Some species in northern Australia build razor-backed structures that point north, maximizing the thermal comfort of those within. And in many species of termites the water provisioning, highway construction, and air conditioning of their great edifices rival in sophistication anything built by humanity.

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    The Age, December 2, 2005.

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