Spiders, Michael Chinery, with illustrations by Sophie Allington (1996)
Spiders are special: they spin. And they’ve been doing so for millions of years. Their speciality is the root of their name: spider is from Middle English spither, meaning “spinner”. The root is even more obvious in German: Spinne. Not all languages call spiders spinners, but then not all spiders obviously spin. Some don’t make webs, though “all species protect their eggs by packing them in silken cocoons” (pg. 24). Not all spiders use venom either, but all of them are predators, mostly on insects and other arthropods, sometimes on larger prey like lizards, birds, and even fish. That is another part of what is interesting about them: like all predators, they are lurkers on the threshold between life and death. Spiders are dedicated death-dealers and sophisticated slayers. To see that dedication and sophistication in action, just watch a spider spinning its web. It will be using a minute brain to follow complex but flexible rules, because invariable webs would not fit an variable world. This is why spiders, like human beings, need nervous systems: web-making is an instinct, laid down in the genes, but instincts have to be triggered and adjusted according to the messages in sense-data.
One thing needing adjustment is the kind of silk used: you’ll learn from this book that in most species “individuals possess between three and six different kinds of silk” (pg. 25). It ranges from pyriform and ampullate silk, extruded from the “anterior spinneret” and used for webs and life-lines, to aggregate and flagelliform, extruded from the “posterior spinneret” and used, inter alia, for the sticky threads of orb-spiders’ webs. There’s also cribellate silk, produced by the cribellum, or “little sieve”, a special organ in the cribellate spiders:
The cribellate spider produces perfectly normal silk from its spinnerets and then covers them with the cribellum silk, which is brushed from the cribellum by a compact patch of bristles, called the calamistrum [Latin for “curling-iron”], on each hind leg. Each bristle carries several rows of microscopic teeth and acts like a minute hair brush. The cribellum silk forms ribbons but, because the legs vibrate rapidly when brushing, the individual threads – only 0.000015mm in diameter – are thrown into microscopic loops… Any insect unfortunate to touch the ribbons quickly gets its feet entangled in the loops and is held fast – without any glue. (“Spider Silk”, pg. 28)
Sticky aggregate silk is a chemical solution to the problem of catching prey; entangling cribellate silk is a physical one. Neither has been consciously designed: evolution did the work by selecting and rejecting millions of individuals down millions of generations. It’s important, and awe-inspiring, to remember that spiders and humans have a common ancestor that didn’t use silk. The spider-line, step by unconscious step, perfected the manufacture and manipulation of silk; our line, step by less unconscious step, perfected the manufacture and manipulation of mind. That’s why human beings write books about spiders and not vice versa. But both lines, the arachnid and the human, were undertaking a mathematical journey: we followed complicated trajectories in multi-dimensional information-space, or rather our genes did. Natural selection, and its odder and sometimes antagonistic cousin sexual selection, are editors of a microscopic text called DNA, which lays down recipes for brains, bodies, and behaviour.
Most natural history books describe what is cooked by DNA, not the genetic recipe itself, but then the cooked product is the most obvious thing and what we’ve been familiar with longest. But all biology, whether it’s studying bats or beetles, frogs or fungi (or dragonflies), is about evolutionary variations on an organic theme. DNA is like a giant recipe-book or giant musical score: each species is a particular dish or particular melody. Higher biological divisions are like styles or genres: spiders taste or sound similar, as it were, and they harmonize with scorpions, mites, and ticks, other eight-legged members of the class Arachnida. But the harmonies extend further and terrestrial life can be seen as a giant symphony played by the orchestra of evolution. If we discover life away from the earth, we’ll find it playing a half-familiar tune: mathematics, the Magistra Mundi, or Mistress of the World, will have been waving her baton there too and Richard Dawkins suggests that Darwinian evolution may be a universal principle, as the only means for life to arise from inanimate matter.
Or the only means until we can create life ab novo, that is: human beings are on the verge of being able to synthesize life from chemicals. Intelligent design, a fantasy of the anti-Darwinists, will soon become a reality in human laboratories. It will be further proof of the praeternatural nature of humanity, but this book provides proof of that too. Pages sixty-four to sixty-five, for example, illustrate the arachnid instinct of web-making using the human skill of drawing. One of the attractions of the book is that, apart from a photograph of the yellow-and-black orb-spider, Argiope bruennichi, on the front cover, all the illustrations are hand-drawn, from the anatomical cross-section of a typical spider on page twenty-three to the “balletic courtship dance of a jumping spider” on page eighty-seven. You can admire the sophistication of Sophie Allington’s drawings rather in the way you admire the sophistication of a spider’s web, though the credit of a human’s abilities generally accrue to the individual, rather than to the species. But is drawing a Darwinian activity like web-making? That is, is it a means of enhancing the survival of an individual and the transmission of the individual’s genes? One big difference between drawing and web-spinning, of course, is that not all human beings draw or create other forms of art. And human beings will not have specific genes for drawing in the way that we have specific genes for language. Which is another praeternatural part of human nature: all other forms of life use a symbolic code to survive, because DNA is a symbolic code, but human DNA allows us to use a second symbolic code, language – and sometimes a third, mathematics.
The mathematics in this book is implicit, but Michael Chinery supplies the explicit language. Although his prose is not as obviously and powerfully admirable as the illustrations, it provides the most meat for the mind and the imagination:
Bolas spiders, also called angling or fishing spiders, live in North and South America, Africa and Australasia. Odd-looking creatures whose squat bodies are often studded with horns and “warts”, they are among the very few araneid spiders whose bites are potentially dangerous to people. Typified by Australia’s Dichrostichus magnificus, commonly known as the magnificent spider, they cling motionless to leaves and twigs by day and don’t stir till nightfall. Hanging from a short thread attached to the underside of a twig, each spider pulls out a “fishing line” about 5cm (2 inches) long and carrying one or more blobs of very sticky glue. Whirling the line about with one of its legs, the spider waits for a moth to take the bait. This seems a bit of a hit-and-miss method, and pretty tiring as well, but the spider has a secret weapon in its armoury – a scent just like that released by certain female moths. The male moths can’t resist it and come flocking to the spider’s line… The bolas spider does not usually need to whirl its line around for more than a few minutes each evening. (“Finding Food”, pg. 71-2)
This hunting technique is ingenious, effective, and entirely undesigned: lying isn’t confined to human beings, because this type of spider is lying with a chemical, rather as human fisherman lie with baited hooks. Other spiders fish more literally: the European aquatic spider, Argyroneta aquatica, “inhabits ponds and slow-moving streams all over the temperate regions of Eurasia” (pg. 48-9). It builds a “domed web” underwater, fills it with air from the surface, and uses it as a base for hunting and chamber for feasting: “water would dilute the digestive enzymes poured onto the prey if the spider tried to dine in the water” (pg. 49). But digestive enzymes don’t just help spiders feed: they help spiders overwhelm their food. Like snake venoms, spider venoms are a kind of super-charged saliva, designed to deal death rather than simply help with digestion. Webs are not complete solutions to the problems of predation: large insects can break free, given time, or fight back when cornered. Venom is a force-multiplier, or rather a force-nullifier. And it is a sinister thing to see in operation, as a non-scientific observer of spiders, John Betjeman (1906-84), described in his poem “The Cottage Hospital”:
…Apple and plum espaliers
basked upon bricks of brown;
The air was swimming with insects
and children played in the street.
Out of this bright intentness
into the mulberry shade
Musca domestica (housefly)
swung from the August light
Slap into slithery rigging
by the waiting spider made
Which spun the lithe elastic
till the fly was shrouded tight.
Down came the hairy talons
and horrible poison blade
And none of the garden noticed
that fizzing, hopeless fight.
(from A Few Late Chrysanthemums, 1954)
The beauty of a web, and sometimes of the web-mistress too, combine unsettlingly with the deadliness of its purpose: spiders are like tiny vampires. But they aren’t very dangerous to man and it’s puzzling that one of the commonest phobias, arachnophobia, should be inspired by them. There are a lot of arachnophobes in countries that don’t have dangerous spiders and their phobia can seriously affect their lives. Is it an exaggeration of an instinct that was written into our brains long ago, when we were smaller and more vulnerable creatures living in the tropics? Perhaps. I like the idea that human beings have records of spiders not just in our books and idioms, but in our DNA too, transmitted from generation to generation since we left the trees of Africa. For example, I like and am fascinated by spiders, but I am still startled if I see a large spider unexpectedly close at hand, even though I know that no species in Britain is dangerous and that none will bite without being provoked.
But fear is a potent, and piquant, spice at the spider-feast. Spiders are like snakes and sharks: interesting in part because they are associated with pain, injury, and death. This book discusses that aspect of their natural history and much more beside. Its chatty text and attractive illustrations make it an excellent introduction to a strange and wonderful family of animals, and to biology and evolution in general. Spiders have existed long enough and widely enough to have diversified into all manner of ecological niches, from parasitism to mimicry. Some spin silk, some squirt it. Some catch prey, some steal it. Meet them all in this set of symbols and codes.