Nonfiction | September 01, 1998
We must have . . . objects themselves to serve as the factual basis for knowledge, the final arbiter in matters of contested identity or meaning, the ‘ground truth’ that underlies our understanding of the world we inhabit.
–Anna K. Behrensmeyer, Acting Associate Director for Science, National Museum of Natural History, the Smithsonian
During a stretch of Washington months I got to know, tolerably well, a big beautiful spider. She was blotchily orange and tan with darkly banded legs. Each day she spun a fine new round web somewhere in the garage, or occasionally on the back porch. She usually sat off the web, hidden against the ceiling or a protecting beam. Her eyesight was none too good, but when moths and flies blundered into her trap, she could feel the vibration of one of the web’s guying threads and she would rush out onto it. She would eat the first of her catch and wrap the rest in silken winding sheets to keep for later. I always tried to avoid tearing her web and save her repair work, but she was a quick and efficient spinner. Jonathan Coddington, Curator of Spiders at the Smithsonian’s Natural History Museum, told me that she ate each day’s web and reprocessed the protein in it. Within twenty minutes of munching it down she was capable of recycling the silk.
Her common name is barn spider. Her scientific one is Araneus cavaticus. Her genus, Araneus, includes a greater number of spider species than any other spider genus. It, and the name of her family, Araneidae (the spiders who spin orb-shaped webs), as well as that of her order, Araneae (all spiders), and even her class, Arachnida (spiders plus a lot of their kinfolk: ticks, daddy longlegs, scorpions and suchlike), echo the name of Arachne, a Lydian princess. Arachne was such a skilled weaver that the goddess Athene, who fancied herself as the best at that art, grew jealous of her. The goddess, determined to find technical fault with Arachne’s work, examined one of her tapestries, into which she had provocatively woven a story of the love affairs of the gods. But Athene could find no technical fault, none whatsoever, no matter how hard she tried. That made her even crosser and, furiously, she tore up the work (No one ever said the gods were nice). The princess, terrified at having aroused the fury of a goddess, hanged herself with a rope on a rafter. Athene, still irritated and not sufficiently satisfied with the mere death of an irreverent rival, turned her into the animal she hated most of all, the spider, and transformed her rope into a cobweb.
As spiders go, A. cavaticus is famous. She is the heroine of E.B. White’s book, Charlotte’s Web, in which she saves the life of Wilbur the pig by writing messages in her web. I never did see TERRIFIC embroidered in the garage, but for someone like Jon Coddington, the barn spider’s web does have messages. Jon is a specialist in spider taxonomy and behavior.
Today’s taxonomists aren’t just in the business of assigning names to newly discovered animals; instead they are folding into the classification scheme everything heritable known about a particular animal and its relationship to all other animals. They ponder zoological principles and ask questions. What constitutes spiderishness (Order Araneae)? How does one family group of spiders differ from or resemble the others (Families Araneidae and Theridiidae)? What is the evolutionary relationship of the groups of spiders that spin different kinds of webs (Charlotte and all the rest)? The pictorial representations that result from asking these questions are not simply a classification scheme but are more like a densely packed encyclopedia of current biological knowledge, subject to revision and editing as new discoveries are made, and readable by anyone with some understanding of the animals diagrammed. They are family trees that show which animals are “sister groups”; degrees of cousinship; who kept certain anatomical features or ways of doing things; who invented new ones.
In asking these questions, Jon settled a long controversy about spider phylogeny, or evolutionary trend. Spiders spin a variety of webs peculiar to their own kind. Sheet-web spiders (family Linyphiidae), for instance, make the webs that look like little flattened hammocks that you often see in the shrubbery in the early morning when they are frosted with dew. Spiders of the family Theridiidae spin those cobwebs that people tidier than I am dust out of basement corners. My A. cavaticus and others in the family Araneidae spin those familiar orb-shaped webs of Halloween art.
It had long been assumed that orb webs were the highest achievement of spiderly craft and were the most advanced. Such webs look so perfect to our eyes that they were thought to be maximally efficient, possessing such adaptive value that their making had evolved independently in different groups of spiders. They were certainly worthy of the sort of spider who could lay out SOME PIG in her web.
After careful observation, however, Jon inferred that rather than being the ultimate web, the orb web is primitive, ancestral. It is the kind of web that spiders first started spinning. And the scorned, messy-looking (to our eyes) cobweb is more elaborately engineered, denser, more protective, and more efficient for trapping prey–which is, after all, the purpose of a web. All spiders are carnivores. Jon concluded that the cobweb evolved from the orb web; other more specialized webs are derived from the orb web, too. Earlier spider classification that separated orb weavers into different groups based on anatomical differences have been generally scrapped now, Jon told me, because putting all the orb weavers together better represents what we know about them.
I sat in Jon’s office on the third floor of the Smithsonian’s Natural History Museum as he explained all this to me. The sun flooded through his windows overlooking the Mall beyond. Jon is a tall, lanky, rumple-haired young man with glasses and a lopsided smile. He was dressed in an open-necked shirt, khakis, and Birkenstocks.
The Natural History Museum is one of the most popular stops for tourists when they visit Washington. More than five million visitors come there every year. Afterwards they probably remember the elephant in the rotunda, the nice lady at the Information Desk, or dinnertime for the tarantula at the Insect Zoo. But what they will not remember, for they will not have seen it, is the undisplayed 99% of the collections of 122 million “objects,” like millipede and earthworm specimens I’d seen on other visits to the Smithsonian and its support center in Maryland. Neither do they see the 400 scientists and technicians, people like Jon, who work with those “objects.” Together, the scientists, staff, and collections make up the largest museum in the nation and one of the pre-eminent research institutions in the world. Security in this non-public part of the Smithsonian is tight, as it is in all government buildings, and casual visitors, for obvious reasons, can’t just wander in and start pulling out drawers of collection cabinets. You need a special invitation, and even then you have to go through Security, turn over your driver’s license as bond, assume a visitor’s badge, and have an escort. The escort is needed to find your way through the maze-like hallways threading in between collection cabinets and tiny, crowded offices. The entire behind-the-display area smells faintly of moth crystals and preserving fluid. Jon is the first spider expert to be appointed at the Smithsonian, and his presence means that the spiders are getting a good and much-needed sorting out.
Zoologists’ offices are always stuffed with books, files filled with papers, and stacks of journals, and Jon’s is no exception. But it also has fanciful wire sculptures of spiders in their webs and real but dead spiders floating in alcohol in collection vials. Spiders, spiders, spiders. Spiders everywhere. He showed me a flat container with a web in it, but not its spinner. The web had been made by a brown recluse spider, whose bite is as dreaded by many people as that of the black widow. He had been working with researchers from Dupont, who were interested in developing threads that would have the same strength and other qualities as spiders’ silk.
They had been concentrating their research on the golden silk spider, a neotropical orb weaver famous for its strong web. “But I think there are others worth studying,” said Jon. “The brown recluse may be a better bet.” The web in the flat container looked dense. He showed me some scanning electron microscope photos of the unusual, blunt spinneret that is part of that spider’s silk-making equipment. The silk from it comes out flat and ribbon-shaped, not thread-like as with other spiders. “We don’t know much about its qualities yet, but it is worth investigating,” Jon said.
Jon’s desk was covered with collection vials containing specimens he had found in East Africa. He spends about half of his time out in the field collecting and studying spider behavior. He identifies them to, usually, no more than the family or genus level. “I leave the determination of species to someone who specializes in that group,” he told me. He notes down the collection data and then passes the spiders along to a colleague who enters the information into the computer record and prints out labels that identify them and tell the when and where of their collection. Groups of individual vials containing the new specimens are packed into straight-sided, half-liter, alcohol-filled bottles resembling old-fashioned canning jars because they are closed with rubber gaskets and metal clamps.
Jon took me back to a room filled with tan metal cabinets that looked like map cases with fat drawers, the ones I’d seen millipedes stored in previously. Within the drawers the half-liter jars of spiders are stored, arranged alphabetically by family and subdivided into genus and species, if those are known, and geographic origin. Jon pulled out a drawer containing A. cavaticus specimens. There were two vial-filled jars of them, but many more of other species of Araneus. All told, Jon estimated, the museum’s spider collection contains some 116,000 specimens.
The entire entomological collection, which includes not only spiders but insects and myriapods, contains thirty times that number, or 31 million specimens. “It is,” Jon told me, “one of the most inclusive and accessible entomological collections in the world. The only other one of equal importance is the one at the British Museum.”
Specimens, preserved and classified, make up what is called a synoptic collection. That means that it is made up not of every single thing that is, but of a synopsis of everything, a holding of representatives of taxa from all over the world. “Our museum,” said Jon, “contains the greatest synoptic collection of spiders and other terrestial arthropods on earth. This is where biodiversity can be studied.” Each year some nine thousand scholars visit the museum to make use of collections such as this one.
One famous researcher who made just that sort of visit was Hirohito, better known then as a divine emperor than as a marine zoologist. When he came to Washington on a state visit in 1975 he was keen to examine the museum’s coelenterates, a sampling of the hydra, jellyfish, sea anemones, and corals of the world, to clarify some of the species in his own collection. So keen was he, in fact, that once he began work he overstayed the brief time his State Department handlers had allotted and, to their distinct annoyance, refused to leave until he was done. Ellis Yochelson, the museum historian who tells this story, commented, “This may be one of the few times that protocol has given way to natural history.”
Researchers can borrow from the museum. In 1996, more than 140,000 specimens from the entomological collections were sent out on loan. “Let’s say someone is trying to revise a group,” Jon said. “He has two females at a certain taxonomic level and no males. He needs a series to make the identification, so he borrows what we have.” A loan is normally made for two years but can be renewed, and sometimes specimens are kept ten, even fifteen years by qualified researchers.
Back in his office, Jon pointed to the fancy work of the brown recluse and said, “Good taxonomy has predictive value, which is often useful. For instance, there is a spider in South Africa known as Sicarius [the name means “murderer”] that can give a serious bite. No one has done much work on it and we don’t know about the species, but we think the genus Sicarius is sister to genus Loxoscelles, the genus to which the brown recluse belongs. We do know rather a lot about the brown recluse, so we can make predictions about the biology of Sicarius and know how to treat the bites.”
Bad taxonomy, on the other hand, can be expensive. Many millions of dollars have been spent to attempt to eradicate the gypsy moth in this country; it was imported from Europe a little over a century ago as a consequence of what we now know was mistaken taxonomy. Leopold Trouvelot, a French amateur naturalist and astronomer, was using the gypsy moth in an experiment to develop a better silkworm when his European specimens escaped from his laboratory near Boston. Undeterred by natural predators, gypsy moths have been eating their way through our eastern forests ever since. At Trouvelot’s time, the gypsy moth was classified in the genus Bombyx, that of the silkworm, which was, and still is, Bombyx mori. The gypsy moth was, but no longer is, Bombyx dispar (which means “silkworm with males and females that look different”). Trouvelot thought that the two moths were close relatives because of the taxonomy, may even have considered attempting to interbreed them. He probably would not have experimented with the gypsy moth (kept in fair check in Europe by its natural predators) had he known it by today’s name, Lymantria dispar. The genus name means “destroyer.” Today’s taxonomy takes into account its evolutionary history and puts it, along with the other tussock moths, in the family Lymantriidae, a considerable relational distance from the family of silkworms, the Bombycidae.
All the invertebrate zoologists I have ever talked to have lamented the state of taxonomy in their own particular fields. In many of them the basic relationships have never been worked out at all, and others need to be brought up to date–the process is called “revision”–to be adjusted to evolutionary thinking and to incorporate the considerable new information that tools such as molecular analysis are able to give. One eminent authority, E.N.K. Clarkson, has estimated that of all the described species known, only about one-sixth of them are “good,” that is properly defined species in the sense that we know for sure that its members don’t interbreed with others.
“The folks who think taxa are hypothetical or human constructs,” Jon said, “are just wrong. Many taxa on earth are a programmed to need, hunt and depend on other particular taxa. So flies, molds, viruses, worms, bees, and so on ‘agree,’ as it were, with human taxonomists. When specific identity is important, it usually turns out that we are all (humans and whatever else) in agreement. We are a natural order that exists independently of the observer.”
But, in addition, the bits and pieces of life are so many that we need to order and classify them before we can think about them. We have the sorts of brains that cannot handle the world in the raw. We have to arrange all the bits into piles, and if there are too many piles, we arrange those into clusters. Without ordering systems, which is what taxonomies are, we can’t think, live, or work with our world. We would find it hard to make our way through a shopping list at the grocery store if we didn’t have mental categories.
Without, say, the category “orange,” we would have to remember each time we shopped that we wanted those orange-colored things with sweet pulp inside, and not the yellow-colored things with tart pulp inside. What is more, we want the oranges and lemons grouped together so we can think of them as “citrus.” And please put all the fruit and vegetables together in one big section and call it “Produce,” not mixed up with the coffee and kitty litter. That’s taxonomy. And the categories, whether they are called Oranges, Citrus, and Produce, or species, genus, family, order, and class, are taxa. Singular: taxon.
From Aristotle to Foucault, the world’s heavy (and sometimes not-so-heavy) thinkers have seized upon taxonomy and ordering systems as an intellectual and practical joy. It is so much fun to create neat systems! In another part of my life I was a librarian. Librarians make a profession out of arranging things. They put those mysterious letters and numbers on the spines of books so that they can be arranged on shelves in order of the subjects of their contents. The systems of arrangement in this country, usually, are either the one used by the Library of Congress, a couple of letters and then a number, or the Dewey Decimal System, numbers only. But other systems have been invented by classificatory minds at work. I remember learning in library school about one particularly stunning system called Faceted Classification; it was invented by an Indian whose name I no longer remember. In his system, books were assigned a number that put them on shelves so that they had a relationship by subject not only to the books on either side of them, but also to those on the shelves above and below. The only trouble with his system, and that was perhaps considered a minor one to such a systematist, was that books could never be removed from the shelves because that would break the pattern of relationship. In hindsight, many historical attempts to arrange the natural world seem as contrived and as bizarre as the Facted Classification System, but then two hundred years from now our systems, reflecting as they do the way we look at the world, may seem equally as amusing.
Aristotle’s approach to animal classification, using a single characteristic (those with blood, those with hair) dominated scientific thinking down through the centuries and still, in many ways, influences the way we look at the world to this day. Linnaeus was also a single-characteristic classifier. He divided insects by their wing style, for instance. And we still use several of his names for the insect orders, such as Lepidoptera, the scaly-winged, for butterflies and moths. When you use just a single characteristic you can arrange things by other single characteristics, too. Linnaeus thought wings were important, but a pupil of his, Fabricus, thought that when it came to insects, jaws were all, and he regrouped the insects into piles by the kind of jaws they had. In the Linnaean world it was believed that there were only 9,000 species of all living things, so it was comparatively easy to restack the piles. A relict of Fabricus’ classification scheme lives on in our name for the order to which dragonflies belong, Odonata, the tooth-jawed.
These single-characteristic ordering schemes, Aristotle’s, Linnaeus’, Fabricus’ or any of the others are rather like a game of Twenty Questions and are still found in botanical keys: stems: fuzzy or smooth? leaves: opposite or alternate?
We’ve mostly discarded Linnaeus’ original classification system but we’ve kept his most important invention, which was the custom of giving everything a two-part scientific name. Those names may seem hard ones in these days when people are no longer familiar with Latin, but they are an enormous improvement over the kinds of names given before Linnaeus. Before his time, for example, the honey bee was known as Apis pubescens thorace subgrieseo abdomine fusco pedibus posticis glabris utrinque margine ciliatis. But clever Linnaeus saw it could all be done with just two words. One word, the last, the species name, could isolate animals that were like no others; the first word in the scientific name, the capitalized one, the genus name, could group individual species with others to which they were similar. So the honey bee became simply Apis mellifera, the sweet bee.
Other thinkers had other ways of looking at the world. The eighteenth-century French naturalist, Michel Adanson, believed that those single-characteristic ordering systems were “artificial” and he developed a Universal System that made use of all known characters. He believed that such a system was more “natural,” but in his time it was considered too unwieldy, and Adanson was labeled an eccentric. He sounds like an endearing man. Toward the end of his life, he asked that his grave be marked with a garland of flowers from the fifty-eight plant families he had elucidated.
Many others looked for natural systems, too. They believed that life’s mystical unity could be revealed if only the presumed affinities between the bits of it could be arranged in the correctly discovered configuration. One such system was called the Great Chain of Being, a ladder-like arrangement with fire, water, and air at the bottom, extending through the “lowly” plants and animals with man triumphant on the top step. Then there were the Quinarians, who held that all life could be divided into systems of fives: five circles arranged in a greater circle. Affinities were found where the circles touched, or “osculated.” Each circle could be subdivided into additional fives. Take, for example, the circle of five six-pointed stars that represented the family of crows and ravens. Symmetry was maintained by declaring that certain unfilled points on some of the stars represented undiscovered crows (which tells more about the human mind than it does about crows).
Goethe is one of the best known of the thinkers who hoped to work out a natural system of ordering the world. Coiner of the word “morphology” to mean the study of organic form, his interests were botanical. With a bow toward Plato, he believed that all plant forms could be derived from an Ideal, a dawn-plant, an Urpfanze, which could be thought into a greater reality.
Goethe notwithstanding, no one until Darwin considered organisms except as they existed, fixed in form at the par-ticular moment. The most empirical classifiers examined body parts, measured genitalia, compared color, speculated on the function of organs of the dead specimens to hand. Darwin’s evolutionary thinking forever changed ordering schemes by in-troducing the principle of time, of history, into natural history. An animal’s origins, its lineage, began to be taken into account.
Today’s taxonomy goes by the name of cladistics and the pictorial representation of it is called a cladogram. It comes from a word in Greek for a tree’s branching. Cladistics is a process, an analysis by which taxonomists try to discover the valid evolutionary tree based on the search for traits shared by organisms. It is likely that unique characteristics evolved at different times, so the visual charting of their appearance in a group gives a branching diagram on which ancestral species are inferred at the branches. It defines a given taxon by making use of unique traits, thought to be of recent heritable origin, that set apart members of that taxon from any other taxa on the family tree.
The analysis makes use of everything heritable known about the animals within the group (the ghost of Adanson, this time equipped with a computer, walks): bodily form, biochemistry, manner of living, molecular profile, range, development. To demonstrate the scope of this knowledge with respect to one order, Jon pulled out from a pile of papers on his desk a computer printout that he called, proudly, “THE matrix.” It contains 49,000 “potential cells,” bits of information on spiders he and his colleagues have gathered. These serve as the characters for cladistic analysis among spiders. They are coded digitally so that they can be sorted and compared by computer.
At any taxonomic level, some characteristics are considered primitive, general, shared by all members of that group, and for that particular analysis they are ignored. All Arachnids have eight legs, so if you are studying spiders, the character “having eight legs” would be ignored. But other characteristics peculiar to spiders alone, such as having spinnerets at the nether end or having poison fangs, a head and then the rest, attached by a narrow waist, would be considered. Those help define spiderishness. Within the order of spiders, narrow-waistedness and spinnerets at the end would be ignored and considered primitive because all spiders evolved from animals of that sort, and some other more special characteristic would be considered derived.
I asked Jon what would separate the more efficient and more lately evolved cobweb spinners, the Theridiidae, from primitive orb weavers like my A. cavaticus. He said that cobweb makers hurl big droplets of sticky silk to attack their prey. A. cavaticus can only hang sticky silk in its web. The sticky silk trick is always the same for all cobweb makers, whatever their species. It is a unique character, a derived character.
Cladistic analysis is not even half a century old. Its basic underpinnings, called phylogenetic systematics, were worked out by a German entomologist named Willi Hennig, who died in 1976. Hennig knew that change and flux is characteristic of life; that a bug is often a little squirmy, worm-like thing when it is young and in larval form, but becomes a winged beauty as a mature, reproductive adult; that many marine invertebrates, such as the barnacle or sponge or coral, float freely in the plankton when immature but change in form and settle down as firmly as a plant after they grow up. He also knew that classification systems in the past had been based on dead specimens, fixed for all time in preserving concoctions at a particular stage of life, and that, as a result, sometimes the same animal, larva and adult, had been given separate species names. He wanted to develop, not so much a classification, but what he called a “general reference scheme of biology” that took change, took entire lives and the way they were lived into account. He wanted to incorporate paleontology, geology, and biogeography into biology.
Hennig was held prisoner by the British in Italy during World War II and it was there, in prison, that he started putting down his thoughts on the subject by hand in an Italian notebook. His massive Grundzüge einer Theorie des phylo-genetischen Systematik was not published, however, until 1950 by an East German publishing house (he lived in West Berlin but worked in East Berlin) on “poor paper . . . written in a style of language which is difficult to read, even for Germans,” according to Dr. Michael Schmitt of the Museum Koenig, who is working on a biography of Hennig. Dr. Schmitt, with whom I correspond, also wrote that Hennig’s work was “overloaded with philosophical . . . stuff.” Hennig’s ideas were pretty much ignored after its publication. In 1961, as a personal protest against the building of the Berlin Wall, Hennig quit his job with the German Entomological Institute in the eastern part of the city “on 13th August, the last day practically possible,” wrote Dr. Schmitt dryly, and sub-sequently became director of phylogenetic research at the State Museum of Natural History in Stuttgart. A decade later an English language version of his work appeared as Phylo-genetic Systematics and was taken up by scientists and began to be used. Today, in revised form, it is the standard tool for analyzing relationships in the living world for museum and university scientists nearly everywhere. Hennig did, indeed, create a “general reference scheme of biology.”
I asked Jon what he thought about all the huge numbers of species estimated to exist and what the effect of those estimates were for a museum curator. “Actually I’m not too interested in species,” he said with a dismissive wave of his hand. “It’s easy enough to extrapolate those numbers by keeping track of how many new ones turn up with each family or genus actually collected on successive expeditions to any one place. There are something better than 36,000 known species of spiders and perhaps another 100,000 as yet unknown. But the higher taxa represent reality.”
The reality Jon was talking about is apparent already to my four-year-old grandson, who recognizes, when I show him, the separate reality of an ant (Family Formicidae) as distinct from a wasp (Family Vespidae). I think I’ll have to wait a few years, however, before I explain to him the reality of their likeness within the order Hymenoptera.
“Look,” Jon said, “there are only 7,000 families of all kinds of life on this planet. Of those 7,000 families there are 105 that are spiders. We have, right here in the museum, representatives of nearly all of them.”
He is working hard to collect the rest.
“You know what I want to do?” Jon asked me. “I want to create, as quickly as possible, a synoptic collection of the chunk of life for which I am responsible. Because 200 years from now there’s going to be a news conference held here, in the museum. There will be this Minister of Environmental Affairs, who will announce that the Inventory of Life on Earth is complete, that there are 5,748,941 species of everything. And some reporter will stand up and say, ‘But Madame Minister, didn’t they say 200 years ago that there were twelve million, fifteen million, thirty million, even eighty million species?’ And she’ll answer in one of two ways. She’ll say ‘Well, we lunched them all,’ or she’ll say ‘They didn’t know what they were doing 200 years ago.’ I want to make it impossible for her to give that second answer.”
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