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This year, give thanks for spiders

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A garden wolf spider (Lycosa) carries her brood of over 100 babies on her back for protection at Sydney Wildlife World on July 18, 2008. The baby spiders will stay on her back for 30-40 days before molting and moving off or staying and risk being cannibalised. (Photo credit: TORSTEN BLACKWOOD/AFP/Getty Images)

Chances are, you're already pretty upset before you started reading this post. Some of you are likely angry just at being exposed to the featured image for this story. Maybe you think this is some sort of elaborate troll.

It isn't.

It's probably only a slight exaggeration to say that human beings as a species could not survive without spiders; we could survive, but we certainly would not have thrived to the extent we have. The old saw goes that dogs are "man's best friend," but probably no other kind of organism on earth has been more important to the success of humankind as a species than the spider.

Why do we all hate spiders?

As a species, we do a pretty terrible job of properly identifying threats to our survival. We have survived and proliferated in spite of some pretty terrible instincts. We panic over perceived dangers that are loud, unusual, flashy, and cause immediate effect to the exclusion of dangers that are quieter, more common, and take a long time to come to fruition.

For example, the average human panics at the very idea of a tornado, even though the chances of death due to tornado are small (and vanish to almost zero for people who live in modern, brick-based structures and who take reasonable precautions like staying away from windows).

On the other hand, rain — even heavy rain — is accepted as a matter of course or annoyance, even though complications from rain claim far, far more lives than tornadoes. On average, about 80 people are killed per year in the United States in tornadoes, whereas 418 people have been killed by flooding in the last three years (an average of 139 a year).

Far worse, researchers have estimated that as many as 7,400 fatal car crashes occur every year from complications caused by ordinary old, non-scary precipitation. And yet, no one dares to leave their house if they are in the middle of a tornado warning, whereas driving in the rain usually doesn't merit even a second thought.

But the pattern holds: tornadoes are a) unusual, b) loud, c) visually jarring, and d) cause immediate damage. Therefore, they are an object that we fear far less than rain, even though ordinary rain does far more damage.

Thus it is with spiders. Getting bit by a spider is an unusual event. Spiders, for all their benefits, are visually jarring. And when you get bit by a spider, the venom causes some kind of instant reaction (although in almost all cases, also not life threatening or even serious). So we have developed an instinctual fear of spiders. Many of us will go out of our way to kill spiders even if they aren't interfering with our lives in any way.

This is a tragic mistake.

Are spiders really harmful?

Well over 99 percent of spiders pose absolutely no threat to humans whatsoever. The few species of spiders who are aggressive toward humans do not have venom that is dangerous to life or limb for humans, and the few spiders that have dangerous venom are not aggressive toward humans. The overwhelming majority of spider species are neither aggressive toward humans nor a serious threat to life even if a spider bite occurs.

Even the deadliest spider in the world, the black widow, is not nearly as dangerous as most people assume. In the first place, like almost all spiders, it will only bite humans if it feels threatened (which usually happens in freak accidents like someone unwittingly sitting on one). However, even if you happen to be one of the very few people unlucky enough to be bitten by a black widow, modern medicine has rendered this spider almost completely non-fatal. It has been over a decade since a single person in the United States has died from a black widow bite. Worldwide mortality rates for black widow bites have dropped to less than 1 percent.

If you get bitten by a spider, you are simply not going to die unless you are a) very old, b) very young, c) have an unusual allergic reaction, and/or d) refuse to avail yourself of any medical treatment. It really is that simple. In most cases, spider bites — even from extremely venomous spiders — do not cause serious, lasting harm.

What would life be like without spiders?

Pretty terrible. While a comparatively infinitesimal number of humans have ever been killed (or even seriously hurt) by spiders, they are the most effective predator of the deadliest animal in the world (to humans). No, I'm not talking about the lion, the tiger, or the bear; I'm talking about the mosquito.

Mosquitoes are responsible for more human deaths than all other kinds of animals (including other humans) combined. Some estimates suggest that mosquitoes are responsible for 700,000 deaths per year, and as much as 17 percent of the total spread of human infectious diseases. Before treatment for diseases like malaria became readily available, this number was surely higher, at least as a percentage of the overall human population on earth. In addition to the deaths, millions of people a year develop serious, debilitating illnesses from mosquito transmission — including hundreds of millions of cases of the serious Dengue Fever each year from mosquito transmission alone.

It should be noted that the symptoms of Dengue Fever are more serious — and more potentially lethal — than the bite of a black widow spider.

And researchers warn, mosquitoes are becoming resistant to current forms of chemical control, rendering the work of predators like spiders (and birds) even more important in advancing human welfare.

Apart from mosquitoes, spiders are also vital in controlling the population of other insects that are known disease vectors for humans, including fleas, cockroaches, and flies.

It is probably no exaggeration to say that spiders have saved hundreds of millions — or possibly billions — of human lives due to disease prevention alone.

But since getting bitten by a mosquito is a regular occurrence, and since the symptoms of the diseases they carry may take a long time to manifest and cause damage, we nonsensically view flying insects as pests or annoyances, while treating the spiders that eat them as objects of fear and loathing. People object strenuously to the presence of spiders inside their houses, never thinking that the presence of a spider inside almost certainly means the presence of insects that are far worse for you than the spider could ever be.

And actually, controlling disease isn't even the most important thing spiders do for humankind

Unbelievable as it may seem, spiders' work in controlling the insect population serves an even more important function than preventing the spread of communicable disease: It prevents what would otherwise be a massive, permanent global famine.

See, even the insects that don't carry human diseases love to eat. And the favorite foods of many of the most populous insect species are the tasty plants humans grow to eat and feed their livestock as well. Researchers have suggested that without spiders to control the population of crop-consuming insects, the globe would not be able to grow sufficient food to feed the current human population (to say nothing of the fact that the human population continuously grows and encroaches on available farmland). And again, since flying insects are continuously adapting natural defenses to chemical-based pesticides, spiders' work in preventing mass human starvation is likely to be more important than ever in the future.

Furthermore, flying insects don't just carry diseases that affect humans, they also carry diseases that can ravage the herds of livestock that humans eat.

In conclusion, a world without spiders would be a world with rampant disease and famine; a world in which humans would have a much more difficult time surviving and thriving as the dominant species on the globe. Perhaps no other creature has been more vital to our success and happiness, and for that we all ought to be thankful, even if some of them do look like the stuff of your nightmares' nightmares.

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