January 1988: A 56-year-old woman from Spokane, washington, feels something bite her on the thigh. She soon becomes nauseated and develops a migrainelike headache. Her thinking becomes addled. In the days that follow, a patch of dead tissue sloughs from the spot where she was bitten. It is at least two weeks before she seeks help, and by then it is too late. She is bleeding from the orifices, even from the ears. Doctors find her blood deficient in several basic components. Her marrow stops making red blood cells. After lingering in the hospital for several weeks, the woman dies of internal bleeding.
There are other cases.
October 1992: A 42-year-old woman from Bingham County, Idaho, feels the burning bite of a spider on her ankle. She, too, develops a headache and nausea, as well as dizziness. The bite blisters and bursts, leaving an open wound that continues to grow. After 10 weeks, the crater, still growing, is big enough to accommodate two thumbs and is ringed with black flesh. More than two years after the bite, the wound heals as a sizable scar, beneath which veins are clotted. The woman’s ability to walk and stand remains impaired. The spider she found crushed within her clothing was a hobo spider, Tegenaria agrestis, a member of the family Agelenidae.
Agelenids are found in temperate places all over the world, in about 38 genera and 500 species. The hobo spider first appeared in the United States sometime before the 1930s. It spread across the Pacific Northwest and adjacent areas of Canada by attaching its egg sacs to shipping crates that were loaded on trains, hence its name. Its genus name, Tegenaria, means “mat weaver”; its species name, agrestis, suggests the agrarian life it leads in Europe. But in North America the hobo spider can often be found in cities and has made its presence known in ways its European experience never suggested. Hobo spiders, like this young female, have never been known to cause medically significant injuries in Europe. But in North America, hoboes have been blamed for serious symptoms and a few deaths.The hobo, clad in brown herringbone, has a body about half an inch long and a leg span exceeding an inch. Others in its family are hairy or gray and often big enough to straddle the face of a pocket watch. They build flat webs with a sort of billiard pocket at one corner, in which they lie awaiting prey. In Europe and parts of North America, a type of agelenid, the lesser house spider (Tegenaria domestica), is found behind books on shelves, its thick web tearing when a volume is consulted. In the American Southwest, I’ve seen a gray agelenid with long black stripes. Its abdomen is typically an ovoid, tight and ripe as a September plum. This species has eyes that gleam like emeralds in the dark and webs that lie on ground cover like silk handkerchiefs—crisply white at first, but dirtier with time and use. I have seen these spiders rush out when an insect lands on the web and deliver what looks like a kiss to the prey’s head, whereupon it ceases to struggle with shocking suddenness.Soon the spider drags its prey into the funnel of the web, where it is hard for a nosy biped to watch. Usually all I can see are dark masses and an occasional shadowy scrabbling of legs, but I know that the spider injects a venom into the prey that turns its innards into a soup the spider can suck down. The next day I often find a few insect legs littering the edge of the web.
In the upper Midwest, where the outdoors is coldly inhospitable to spiders several months a year, I have often noted another species of agelenid residing in basements, in what looks like a frayed handful of cotton balls. In one such web I noticed a hummock shaped like a human grave formed over the body of some black creature. This carcass was apparently too much trouble to drag over the web’s edge. The spider had simply built over it. These northern agelenids are brown and rapid. I’ve found in their webs creatures as diverse as millipedes and mosquitoes. I touched one web, as delicately as I could, and saw the spider heave itself out of its funnel-shaped retreat and immediately collapse back into it, so fast I could have hardly told what it was if I hadn’t already known. It reminded me of horror stories I’ve heard about spiders emerging from bathtub drains. I withdrew my finger with considerable haste.
The web felt like cloth made of human hair. It didn’t stick to me. This is typical of members of the Agelenidae family, including the hobo spider—their webs aren’t gluey but depend on their deceptive surface to snare insects. What seems a solid, smooth place to land is actually a layered network of filaments. Most insects lack the footgear to negotiate this snare. Their feet fall between the strands, their claws snagging and delaying their escape long enough for the spider to seize them. The spider itself walks on the strands by clasping them between opposing claws.
It’s hard to say how many people have been hurt by hobo spiders because spider bites are remarkably difficult to diagnose. Part of the problem is that they often don’t hurt enough at first to draw any notice. Even when victims develop serious symptoms, they rarely bring the physician the guilty spider. A spider bite is easily classified as a wound or sore of unknown origin. Moreover, 80 percent of the so-called spider bites treated by physicians are estimated to be something else entirely—the bites of lice, fleas, or ticks; symptoms of diseases like Lyme disease and tularemia; or strep or staph infections developing around minor scratches. Even eczema or a vigorously scratched mosquito bite may cast suspicion on some innocent arachnid. When several Americans exposed to anthrax developed skin lesions in 2001, the symptoms were first attributed to brown recluse spiders.
Why do spiders so often get the blame? Part of the answer lies in arachnophobia. People who notice a sore and a spider in the house independently of each other may jump to the wrong conclusion. Serious arachnophobes often report the feeling, which they themselves may recognize as irrational, that spiders are malicious, bent on frightening and harming human victims. Even people without a full-blown phobia can fall into this way of thinking. Yet most spiders, if they’re capable of biting people at all, only bite in defense of self, territory, or eggs.
Another source of confusion is folklore. Stories of venomous arthropods circulate so frequently that scientists tend to dismiss them out of hand. A few years ago, after I wrote an essay on black widow spiders, I received e-mails warning of blush spiders—tiny but deadly red spiders that hide under the seats of toilets on airplanes ready to bite the unwary traveler’s most sensitive parts. There’s no such thing as a blush spider. It’s an urban legend based on a hoax. Its “scientific name,” Arachnius gluteus, which translates into something like “buttocks spider,” is an easy tip-off.
Last year, I received anxious queries about camel spiders, accompanied by a shocking photo of a massively fanged monster as long as a man’s leg. The camel spider, it was said, habitually runs along under camels, leaping up to feast on the flesh of their bellies. Its venom was said to dissolve flesh rapidly. It was claimed that these creatures represented a deadly menace to soldiers at war in Iraq. In fact, camel spiders are harmless, though scary looking. They are known variously as sun spiders and wind scorpions but are really a little-known arachnid order unto themselves, the solifugids. The largest solifugids in the world are about the size of a woman’s hand, which is certainly awe inspiring, but a mere fraction of the size suggested by a photo placed on the Internet. Solifugids rarely if ever bite people—their mouthparts aren’t hinged the right way for it—and they don’t carry toxin. Because their fangs are so massive for their size (proportionally the largest in the animal kingdom), they can rely on mechanical injury to kill their prey.
With such drivel perpetually circulating, it’s not surprising that many scientists and doctors have dismissed more credible spider lore. It used to be said that no spider in the United States is really dangerous, and this view held sway well into the 1920s, despite reports of deaths from the bites of the black widow. The prevailing opinion gradually changed after the experiments of William Baerg at the University of Arkansas in 1922 and Allan Blair at the University of Alabama in 1933. Both men subjected themselves to black widow bites in the lab and suffered horribly. After that, scientists blamed black widows for two sets of symptoms: extravagant pain that spreads rapidly throughout the body and the slow death of the flesh around the bite. We’ve since learned that the second set of symptoms is instead caused by the brown recluse spider.
That ought to have cleared everything up, but bogus new spider facts crop up routinely—that the average person inhales four spiders a year in his sleep, for instance, or that brown recluse bites can be cured with an electrical blast from a Taser. Many myths mix in a pinch of reality. The blush spider, for example, must have been inspired by the black widow, which used to infest outdoor toilets and bite people on the genitals. And the false reports of camel spider venom read like an exaggerated account of the true effects of brown recluse venom.
The truth behind hobo spider bites has been especially hard to determine. Hobo venom produces symptoms similar to those caused by brown recluse venom. When the brown recluse was first identified as dangerous in the 1950s, doctors in the Pacific Northwest began to attribute certain lesions to them. But the brown recluse lives in the Midwest and the South, with a few close relatives in the Southwest; no member of its genus is regularly found in the northern United States.
Graphic by Don Foley
VENOMOUS AMERICAN ARACHNIDSThe United States has five groups of spiders that can cause serious injury. The black widow and yellow sac spider are found throughout the country, although the latter’s range has yet to be mapped precisely. The hobo spider has expanded its range in the Pacific Northwest, while the brown recluse is found in the South and lower Midwest. Other recluses are found in the Southwest. (Legend: Purple, black widow; yellow, yellow sac; red, hobo spider; green, brown recluse; blue, other recluses)
In the late 1970s and early 1980s this mystery came to the attention of toxinologist Darwin Vest, an autodidact whose work on cobras, rattlesnakes, and other venomous creatures had won him respect. While working at Washington State University in Pullman, Vest learned that the local zoology department often received queries about necrotic arachnidism—flesh-killing lesions apparently caused by spider bites. Vest looked into the cases of 75 patients in the Pacific Northwest. He blamed most of the injuries on insect bites, cigarette burns, and other causes. But that left 22 cases. Vest and his team surveyed the homes of these patients, collecting thousands of specimens by hand and with sticky traps. None of the homes yielded brown recluses, but 16 of them revealed healthy populations of hobo spiders. Sometimes a single sticky trap would fill with hoboes in a week’s time.
The presence of hoboes in such numbers was suggestive, but it proved nothing. The average home in any temperate region is likely to host several dozen species of spiders. So Vest decided to bring hobo spiders, and several other suspect species, into the lab for tests. He and his team milked live spiders, using a mild anesthetic and micropipettes, under a dissecting microscope, working carefully so that the spiders could be released unharmed. The spiders were so small that the capillary action of the pipettes was often enough to draw venom from the fangs. When that didn’t work, the researchers sometimes resorted to mild electric shock, using a nine-volt battery to make the venom glands contract and prompt the release of a droplet or two. Since each spider produced only a minuscule amount, the researchers had to milk a great many to obtain a workable sample. Their result: The hobo spider venom produced necrotic lesions in rabbits. To confirm this result, Vest shaved the backs of rabbits and held a hobo spider down on each bald patch, forcing a bite. The lesions that formed were similar to those found in human victims.
The hobo spider is now widely recognized as dangerous. The Centers for Disease Control lists it as such, as do medical textbooks and publications like the The Journal of the American Medical Association. Doctors know the signs of hobo venom—a blistering wound ringed with yellow, like the moon in a halo of smog, often accompanied by headaches and, in rare cases, disturbed thinking.
SPIDER’S MILK Researchers at Lewis and Clark College in Portland, Oregon, draw the venom from an immature female hobo spider using electrical stimulation. The venom is drawn into a thin glass tube (bottom right). Female hoboes produce more venom than males. But the venom of the males is more toxic. The hobo spider is now widely recognized as dangerous. The Centers for Disease Control lists it as such, as do medical textbooks and publications like the The Journal of the American Medical Association. Doctors know the signs of hobo venom—a blistering wound ringed with yellow, like the moon in a halo of smog, often accompanied by headaches and, in rare cases, disturbed thinking.But skeptics remain. In 1998 evolutionary biologist Greta Binford of Lewis and Clark College and some of her colleagues at the University of Michigan tried to replicate Vest’s experiment. When they injected hobo spider venom into rabbits, however, the rabbits developed nothing worse than a red bump. Like several other prominent skeptics, Binford notes that the hobo spider is rarely caught in the act of biting and then taken to a competent specialist for identification. Its appearance is unremarkable, so its supposed victims can’t be expected to distinguish it from dozens of other spiders. In Europe the hobo has never been implicated in human injuries, although its venom is nearly identical to that of North American hoboes.
In four of the cases that Darwin Vest investigated, a hobo spider was captured or crushed near the victim. But Vest noted that one of these victims—the 42-year-old woman mentioned at the beginning of this story—had a history of phlebitis, a circulatory problem. According to Rick Vetter, an arachnologist at the University of California at Riverside, phlebitis sometimes causes necrotic lesions. Vetter also notes that the Australian white-tailed spider, once widely accepted by doctors as a source of necrotic arachnidism, has recently been exonerated. Researchers studied 130 cases of confirmed white-tailed spider bites and found not a single necrosis. Vetter would like to see hobo bites subjected to a similarly rigorous study. He points out that a mistaken diagnosis can have serious consequences: Certain skin cancers, for instance, look like necrotic arachnidism and can be fatal if left untreated.
Even if hobo spiders are responsible for the lesions, their bites may not always be venomous. It has long been known that black widow spiders, like some venomous snakes, can deliver “dry bites” to warn off larger animals without wasting venom on them. Typically, these are followed by a dose of venom if the harassment persists. Vest’s sister, Rebecca, who worked with him in his investigations, reports that hoboes often give dry bites. Widows vary in their toxicity with age, health, and gender, and these factors seem to come into play with hobo spiders as well. For example, male hoboes pack a more potent venom than females. It is typically the male hobo, wandering away from its web in search of a mate at the end of summer, that bites people.
People vary considerably in their reactions to venom. I have been bitten by brown recluses a number of times. Though the stinging sensation that developed after a short delay made it clear that I’d received venom, I never developed a sore or any systemic symptoms, and the same is true of most bite victims. The whole experience was less painful than a mosquito bite—and, taking into account the possibility of mosquito-borne disease, less dangerous. It may be that hobo venom is similarly selective. After all, its function is to subdue insects. It would be comforting to think that a few hundred million years of evolution have put considerable distance between us and our insect kin, but only some of us are immune to insect-killing venoms.
Although hundreds of medically significant cases are diagnosed as spider bites in the Pacific Northwest each year, hard evidence is elusive. Rod Crawford, curator of arachnids at the Burke Museum of the University of Washington, notes that a handful of human deaths have been attributed to the hobo spider but that even a physician’s diagnosis is shaky evidence in the absence of the culprit. Like the recluse before it, the hobo has become what Binford calls “a medical dumping ground”—a default diagnosis when a better one can’t be found.
Agelenids are remarkably tolerant of one another, as spiders go. I have seen a spindly male living on the fringes of a female’s web, suffering no abuse from its larger mate. Perhaps he was helping to guard the eggs. I have seen, too, a bed of wandering Jew covered with 20 or so funnel webs, the inhabitants apparently unconcerned about the proximity of neighbors. But I’ve also seen what happens when two come into conflict: a flurry of legs, then the sudden collapse of one spider, which folds up in the grasp of its enemy. The effect is something like a child’s hand crushed in an adult’s.
As it happens, this tendency for some agelenids to eat others may help explain why the hobo has apparently harmed people in North America but not in Europe. Darwin Vest, who considered pesticides an irresponsible way to control spiders, examined the question of what predators might naturally control hobo populations. The most effective predators proved to be other spider species, like the false black widow (Steatoda grossa) and the American house spider (Achaearanea tepidariorum). Most effective of all was the giant house spider, an agelenid with a leg span as broad as a human palm.
The giant is so closely related to the hobo that the two may interbreed, and it not only preys on the smaller species but also competes with it for food. Vest suspected it was the giant that kept the hobo out of European houses all along. In the past 25 years, the giant house spider has established itself in the Pacific Northwest. Rebecca Vest reports that hobo populations in southern Idaho have shrunk noticeably in that same period. It may be that the hobo, though equally venomous wherever it turns up, simply has fewer chances to bite in Europe. And perhaps the same situation will eventually prevail here as the giant house spider, an unrecognized ally long ago suspected of spreading the Black Death, expands its range across America.
参考资料：www.en8848.com
Many years ago, there lived a very rich man who wanted to do something for the people of his town. But first he wanted to find out whether they deserved his help. So he placed a very large stone in the center of the main road into town. Then he hid behind a tree and waited. Soon an old man came along with his cow.
许多年前，有一个很有钱的人想为他的乡亲做一些事。但是，首先他想知道他们是否值得他的帮助。于，他把一个非常大的石头放在镇上主要道路的中心。然后，他躲在了一棵树，等待着。很快，一个老人牵着牛走来。
"Who put this stone in the center of the road?" said the old man, but he did not try to remove the stone. Instead, with some difficulty he passed around the stone and continued on his way. Another man came along and did the same thing; then another came, and another. All of them complained about the stone in the center of the road, but not one of them tried to remove it. Late in the afternoon, a young man came along. He saw the stone and said, "The night will be very dark. Some neighbor will come along later in the dark and will fall against the stone. "
“谁把石头放在路中心了？ ”老人说，但他没有搬开石头。相反，费了点劲，他绕过石头，继续赶路。另一个人来了，做了同样的事情;然后来了一个又一个。所有这些人都抱怨石头挡在路中间，但是没有一个人试图将其搬走。黄昏时，一个年轻人来了。他看到了石头并且说， “晚上是很黑的。天黑时，邻居走来时，会被石头绊倒的。 ”
The young man then began to move the stone. He pushed and pulled with all his strength to move it to one side. But imagine his surprise when under the stone he found a bag full of money and this message: "This money is for the thoughtful person who removes this stone from the road. That person deserves help."
这个年轻人开始把石头搬走。他用劲所有力量连推带拉把石头推倒一边去。而让他吃惊的是，他在石头下发现一个装满金钱的袋子和这条讯息：“这钱是给从这条路上搬走这块石头的深思熟虑的人。这个人值得帮助。”
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Hello! Everyone. Here’s a photo of my family.Look! the girl in red is myself. I’m Gu Tingyan. My English name is Wendy. Please call me Wendy, because I like it. I’m tall and thin. My eyes are big. My hair is short. I like reading, skating, drawing and ...
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感恩节美文《谁是你的守护天使》Once upon a time there was a child ready to be born. So one day he asked God, "They tell me you are sending me to earth tomorrow but how am I going to live there being so small and helpless?"God replied," Among the many angels, I chose ...