Although many people suffer from at least mild arachnophobia, scientists are divided over the precise cause.
Some researchers attribute fear of spiders to an evolutionary survival instinct. In Africa, hundreds of thousands of years ago, our ancestors lived alongside several species of venomous spiders, whose bites, even if not fatal, could incapacitate an individual for days or weeks.
Other scientists say arachnophobia is a learned behavior, due to a childhood trauma or kids observing their parents and siblings getting freaked out by spiders.
Fortunately, arachnophobia is treatable. One study found that subliminal exposure to photographs of spiders could reduce people’s apprehension. (Also see "Tarantula and Bug Petting Zoos Help People Conquer Fears.")
Perhaps it also wouldn’t hurt to appreciate the astonishing beauty of these creatures—which you can now do in this photo gallery—just in time for Halloween.