Tambaqui are seed predators of huge appetite. They migrate into the flooded forest and gather in crowds beneath their favorite food-furnishing species, the rubber tree Hevea spruceana. Like most tree species in the Amazon, H. spruceana grows not in clusters or groves but as widely separated individuals, surrounded by other tree species yet with a large distance between each spruceana. Consequently, a whole gang of tambaqui may simultaneously address themselves to a single spruceana tree. They could conceivably eat every seed that it drops. To crush the hard nut walls of those seeds, tambaqui have evolved large jaws and strong, broad, molar-like teeth. They crunch up the spruceana seeds (which are about as tough as Brazil nuts) and swallow the nut shells as well as the seed tissue—though only the seed tissue gives them any nutrition. A single gorged tambaqui, weighing thirty pounds, might carry two pounds of ground-up seeds in its stomach. That’s like you or I tucking away twelve pounds of peanuts, shells and all, in the course of an afternoon ball game.
The seed-eating piranhas are a bit more fastidious, and it seems to be precisely those pointed, razor-edge teeth that make such fastidiousness possible.
Even the most notorious flesh-eating piranhas—for instance, that large species commonly known as the black piranha—evidently move up into the flooded forest on a seasonal search for food. They aren’t necessarily there for the seeds. In the igapó these flesh-eaters continue to function as secondary consumers, preying upon other fish, insects, occasionally a bird or a mammal or any other animal that might inhabit the forest waters or be so unlucky as to fall in. Black piranha do seem to be omnivorous rather than strictly carnivorous, opportunistic enough to make seeds and fruit a small fraction of their diet when those foods are easily available. But the piranhas that specialize in seed-eating, though closely related, are distinct.
Michael Goulding has identified at least two species of piranha—Serrasalmus serrulatus and Serrasalmus striolatus—that live mainly on a diet of seeds. Each of these species retains jaw and tooth structures almost identical to those seen in its infamous, flesh-eating cousins. Serrulatus and striolatus merely put those structures to different use. According to Goulding: “Piranhas shell the nuts they eat and ingest only the soft seed contents. . . . After the nut wall is broken, the endosperm contents are removed and the shell is discarded. By doing this the piranha does not fill its stomach and intestines with material that cannot be digested but that will take up space. The sharp teeth of piranhas allow them to masticate the soft seed contents into small bits that are usually of nearly equal size.” By slicing through the nut wall and rejecting it, eating only the seed tissue itself (and ignoring also the fleshy fruits in which some igapó trees wrap their seeds), the piranha maximize their nutritional benefit from each belly-load of food. It is a delicacy of appetite that, during the lean times when no seeds are falling, when the fish must live off stored fat, could make the difference for survival.
• • •
Take away those floodplain trees, though, and survival becomes far more problematic.
Timbering, slash-and-burn agriculture, clearing away floodplain forests with the notion of pasturing cattle or planting rice or for other development projects intended to make the jungle “productive” or “habitable” by our civilized standards—all these represent attacks not only on the lowland tree communities but also on the fish species that feed among them. And by Michael Goulding’s estimate, those seed- and fruit-eating species account for something like seventy-five percent of all the fish sold at markets in Manaus and other cities of the basin. Since fish are the primary source of animal protein for the human population there—not just for canny fishermen like Lorenzo, not just for tribes like the Cofan, but throughout both backcountry and urban Amazonia—this whole chain of interdependence is crucial by any standard.
Remove the trees, and you can expect the fish to disappear. Kill off the fish, and likewise some of those tree species (the ones that depend on fish for dispersing their seeds) may not survive. Contrary to common misconception, the soils from which grow the Amazon jungle are very poor, and the rivers draining those soils are also therefore infertile. So the fish that spend half their lives in those rivers depend utterly on the manna that falls in the forest, and on the floods that carry them to it.
It’s just another demonstration of what we already know. The great jungle ecosystems of Amazonia are not a symptom of the region’s richness. They are that richness. Wreck them, and you wreck everything.
SEE NO EVIL
The Fragile Truce Between Man and Scorpion
Allow me to confess an invidious personal bias: I don’t trust any animal with more than six legs and more than two eyes. No rational explanation for this, it’s just a cringe reflex from the murkiest subconscious, but there you are. Six and two. I go queasy with terror and disgust whenever confronted with a beast who flouts those magic limits. Six and two. Octopuses are suspect but acceptable. Insects, however bizarre, are fine. Snakes are among my favorite living things—beautiful, sleek, unadorned, binocular. A dizzying wave of repulsion passes over me, on the other hand, at the mere glimpse of a color photograph of a tarantula. One, two, three, four, five, six, seven, gack, eight—and then the legs. Am I alone or does anyone else experience this neurosis? Have you ever looked a black widow spider in the face? Poison isn’t the problem; a rattlesnake has poison, yet a rattlesnake is merely handsome and dangerous. Hideousness is the problem. I know it’s subjective, I know it’s unfair. But a creature with that many legs and eyes, Judas, you just never know what it might be getting ready to do. One on one, it already has you outnumbered. Spiders are bad enough. Consider, though, the scorpion.
My own heartfelt conviction is that scorpions are perhaps the most drastically, irredeemably repulsive group of animals on the face of the Earth, even including toy poodles. Maybe that’s part of what makes them so interesting.
Scorpions violate the six-and-two rule flagrantly: four pairs of walking legs, one pair of pincers, one pair of leg-like appendages modified to serve as jaws, another pair that are hidden beneath the abdomen like landing gear and perform some still-mysterious sensory function—which makes fourteen limbs altogether—plus anywhere from zero to twelve eyes, yipe, in most species eight, arranged in three widely spaced clusters like Cinerama cameras. The mere listing makes me sweat. And as if that weren’t enough, they also carry a nasty hypodermic stinger hanging overhead on the end of a long tail. Scorpions are more cluttered with obnoxiously useful hardware than a Swiss Army knife.
They travel under cover of darkness. They prey on insects and spiders, as well as the occasional small lizard or mouse. They kill people too—surprisingly many in some countries—though only while defending themselves, or by mistake. A scorpion drops from the thatched roof of a house into a baby’s crib, a young child runs barefoot through a garden, an adult carelessly picks up a piece of firewood, and whammo. In Mexico, at least until recently, more than a thousand humans died each year from scorpion stings. Most of those victims were kids. Another 69,000 Mexicans annually survive a sting that is at least bad enough to report. In Brazil the death rate for young children stung by scorpions is almost one in five, and a single Brazilian city recorded a hundred fatalities in a year. Algeria is another zone of high jeopardy, as are Egypt, Jordan, Turkey, and Trinidad. Scorpions can be found nearly everywhere in the warm latitudes, jungle and mountain terrain as well as desert, but among different species there is wide variation in the potency of the venom.
Some venoms merely cause local swelling and pain. Others attack the nervous system, resulting in high pulse rate, irregular breathing, feelings of fright or excitement, impaired vision, vomiting, and a range of other symptoms of which the final, if it comes to that, is complete respiratory failure. Death by suffocation, out there under the clear equatorial sky.
J. L. Cloudsley-Thompson, a British zoologist who spent part of his career as a museum keeper in the Sudan, described the whole baleful sequence: “First, a feeling of tightness develop
s in the throat so that the victim tries to clear his throat of an imaginary phlegm. The tongue develops a feeling of thickness and speech becomes difficult. The victim next becomes restless and there may be slight, involuntary twitching of the muscles. Small children at this stage will not be still: Some attempt to climb up the wall or the sides of their cot. A series of sneezing spasms is accompanied by a continuous flow of fluid from nose and mouth which may form a copious froth. Occasionally the rate of heartbeat is considerably increased. Convulsions follow, the arms are flailed about and the extremities become quite blue before death occurs.” This progression of symptoms, he says, closely resembles poisoning with strychnine.
Cloudsley-Thompson might be talking about a sting from Androtonus australis, the fearsome North African species said to have venom as toxic as a cobra’s—but he isn’t. He’s talking about an American scorpion called Centruroides sculpturatus. Most infamous of the forty species found in the southern United States, C. sculpturatus is familiarly known as the bark scorpion, from its habit of hiding beneath loose and fallen pieces of tree bark. During one twenty-year period it accounted for sixty-four deaths in just the state of Arizona.
• • •
The Cloudsley-Thompson scenario and that last statistic, though, may both be unduly alarming. C. sculpturatus is quite common in Arizona, and many people are stung by it without suffering any harrowing effects. One of those victims, Steve Prchal of the Arizona-Sonora Desert Museum near Tucson, describes the experience this way: “Take a sharp needle and jab it into your hand. Hold a match or a lighter to it for a couple hours. Then add the needles-and-pins sensation you have when a foot falls asleep. That’s what a bark scorpion sting feels like.” Evidently the reaction can range anywhere from modest discomfort to horribleawful death, depending upon the body size and general health of the person stung, as well as other obscure factors, including luck. Best to steer clear of scorpion habitat, then, when you feel especially frail or unlucky.
Steve Prchal got his sting during a family camping trip, five minutes after having warned the other family members to be careful of scorpions. He reached for a boat cushion that had been drying on top of a bush. Whammo. That pattern seems to be typical. But considering both the number of scorpions and the number of people at large in the state of Arizona, sting incidents don’t happen nearly so often as they might. What makes scorpions a threat to humanity is no special bellicosity on the part of the scorpions but the fact that, because of their shy inconspicuousness, you don’t see them until it’s too late.
They hide during the day, under bark or in rocky crevices or burrowed down into the sand, emerging nocturnally to hunt. They are discreet. If you have ever lain down in a sleeping bag on the warm Arizona earth, you have probably had a closer encounter with these creatures than you realized. Still, on visual evidence you might well conclude that they aren’t really there. Vivid remedy for any such happy illusion can be derived, it turns out, from another strange scorpion attribute: Under ultraviolet illumination, they glow in the dark. They fluoresce. Shine a black-light beam on them and (due to photochemical properties of the scorpion integument about which little seems to be known) they reflect back an eerie greenish-blue radiance. Like a zodiac image in garish neon except that the animal, and the sting, are quite real.
Steve Prchal designed the live-scorpion exhibits at the Desert Museum. He tells of going out on collecting trips, sometimes to a hilly area cut by a certain gorgeous little hidden canyon, down near the Mexican border west of Nogales. Like many collectors, he went at night and used an ultraviolet flashlight, shining his invisible beam along the steep walls of a wash. “It was like stars,” Prchal says. “It would scare the hell out of you to see how many you’d be sleeping with if you camped there.” He didn’t camp there, because he was too smart. I wasn’t, when I lived in those parts, so I did. Saw not a single scorpion. Carried no ultraviolet flashlight. Padded around on the gravel after dark in my stocking feet. Got an excellent night’s sleep. I believe that the phrase Thurber used, in a similar application, was “living in a fool’s paradise.”
Curious about how others have fared among those great scorpion multitudes of the Arizona outback, I decided to consult a couple of postdoctoral desert rats. First I called one Doug Peacock, an eminent monkey-wrench environmentalist and authority on the wild behavior of grizzly bears and humans. Peacock, in his many years of crashing around the desert outback, has collected three scorpion stings, and he remembers them all rather vividly. The first time was the worst. He was tucked into his sleeping bag, somewhere out on the Cabeza Prieta wildlife refuge, and in the middle of the night he chanced to roll over, flopping his arm out blindly onto the sand. Whammo. This one may or may not have been C. sculpturatus—he didn’t get a look at the perpetrator—but the localized pain was ferocious and he went through a few hours of bad headache, nausea, and fever. The third time, out scouting for billboards to chain-saw or bridges to dynamite, he sat down in a clearing and laid his hand back for support—right on a scorpion, which went off like a mousetrap. Either because it was a less toxic species, or because by now Doug was growing immunized, or for some other unplumbable reason, in this case the effects were no worse than those from a bee sting. The second time was perhaps the most interesting. Again on a solo ramble across the Cabeza Prieta, he was sitting up late to read Moby Dick by the light of his campfire. He set the book down, tossed a few sticks on the fire, watched the sparks rise into black eternity, picked the book up, leaned back comfortably on an elbow, and whammo. In his annoyance he pummeled this one to death—in fact, past all chance of taxonomic identification—but a reasonable bet makes it C. sculpturatus.
I also talked with Ed Abbey, whose credentials to speak in any matter of deserts or ornery critters are unequaled. Amazingly, Abbey has only been scorpion-stung once, and that time while sitting quietly on a couch in a trailer house, late one night about a dozen years ago. He was barefoot. He was reading Gravity’s Rainbow. He didn’t notice the scorpion that had come crawling peacefully up. He lifted one foot and set it down again, whammo, but Ed was so engrossed in Pynchon’s novel that all he recalls is tromping the scorpion to death with his stung foot, then quickly fetching a bucket of ice water, jamming the foot into it, and continuing to read. Yes, his assailant seemed to have been that species they call the bark scorpion. Yes, he had some sharp pain at the site, definitely, but nothing much more. On the whole, says Ed, it wasn’t nearly so traumatic as the time a tiny insect, species unidentified, crawled deep into his ear and refused to come out.
There are several morals to be drawn. First and most obviously, heavy reading causes scorpion sting. Second, a person is safer while remaining stationary than in making even the most innocent movement—and safer still if the person remains stationary somewhere outside the borders of Arizona. And a third point to note is that the obliviousness seems to be mutual: They don’t see a human hand or foot coming, those bumbling scorpions, until it’s too late. Otherwise they would surely, like us, prefer to avoid the whole experience.
• • •
They don’t see us coming because they don’t see much of anything. Ironically, despite their superabundance of eyes, most scorpions seem to be almost hopelessly blind. Scientists who study scorpion biology generally mention this handicap (“The eyes are too crude to be of much assistance. . . . The eyesight seems to be of secondary importance. . . . Scorpions have poor eyesight”), which is so pronounced, evidently, that it has been a mystery how scorpions could ever find their way to a meal. Stumbling around blindly out there in the desert, bumping into rocks and each other and Doug Peacock, the poor things should have long since starved to death and lapsed into extinction. Just lately, though, the mystery seems to have been solved.
In a recent issue of Scientific American, Philip H. Brownell has presented impressive experimental evidence for a new theory of how scorpions perceive the presence of food or danger.
They see with their feet.
More precisely,
they rely on pressure-sensing organs near the ends of each of their eight walking legs to detect subtle shock waves that propagate outward, even through sand, when another creature passes by on the desert floor. According to Brownell, the scorpion orients itself toward the focus of any such disturbance by gauging the minuscule differences in the times at which the shock wave reaches each of its eight spraddled legs. Spaced apart, those legs serve as stereoscopic receptors. Take away the sensory input from one or two pairs of legs, or from all four legs along one side of the body, and the scorpion becomes confused. Disoriented. Like a human with only one good ear, and therefore no sense of auditory direction—or with only one good eye, and therefore no sense of depth. Take away all the input from those leg organs, and the scorpion is functionally blind.
They see with their feet. No wonder they need all eight. Okay, this I can accept. But I’m still uneasy about all those sparkling eyes, which seem to serve no purpose except sheer decorative vanity. They don’t walk with them. They don’t depend upon them for vision. Couldn’t they be satisfied with just five or six?
TURNABOUT
The Well-Kept Secret of Carnivorous Plants
Plants that eat animals are looked at, by us animals, askance.
They are perceived as grotesque, menacing, unnatural, horrific—or sometimes just delightfully sinister, in the campy spirit of Vincent Price. Above all, they are seen as aggressive beyond their proper station in life. Their presumptuousness seems Promethean, with us for once on the side of the gods. Nature knows them in 450 different species, and the human imagination has been compelled to invent more. Those imaginary varieties grow to huge elephant-ear sizes and flourish in dense Hollywood jungles, feigning innocence among the other foliage, waiting to clamp closed on a cockatoo or a chimp. Minor-key organ chord while the chimp preens, oblivious, and the big ugly plant drools its caustic juices. Most recently we have Audrey II, the ravenous cabbage of The Little Shop of Horrors. But even Audrey is the epigone of an older model: On the island of Madagascar, according to legend, there lived a man-eating tree.
The Flight of the Iguana Page 5