A common urban legend holds that people eat eight spiders a year while sleeping. Anyone who shares the house with the occasional spider might have wondered how many spiders they eat per year.
Evidence of spider-like creatures dates back more than 300 million years, and it is difficult to believe that spiders would have survived this long if they made poor decisions such as crawling into human mouths.
The claim that humans regularly swallow spiders during sleep is a myth. That said, there is a good chance most people have unknowingly swallowed small spider parts when eating, as many countries allow a certain percentage of arthropod parts in processed food. Some cultures also include spiders in their diet.
We examine the physiology of human sleep and the behavior of spiders to illustrate why this statistic is unlikely to be true.
How Many Spiders Do You Eat in Your Sleep?
So far, scientific studies have not confirmed that people eat any spiders at all during sleep. Although it is not impossible for a spider to crawl into a person’s mouth while they are sleeping, there are multiple reasons why this is highly unlikely.
Busting the Myth of Swallowing Spiders in Your Sleep
It is safe to say that humans would like to avoid eating spiders in their sleep, but spiders would also prefer not to be swallowed. Experts know a lot about how spiders behave, and their insights may reassure people who are worried about spiders at night.
Spiders Keep Their Distance
Spiders are believed to be intelligent beings with a keen awareness of their surroundings. While virtually all spiders are predators, they are also potential prey for many animals. Spiders are generally solitary and would have good reason to stay away from a potential threat such as a sleeping human, which may easily roll over and crush anything beneath it.
Most spiders have poor eyesight, but they can sense vibrations and air currents, and they use these senses to navigate their world. A sleeping human gives off vibrations in the form of a heartbeat, breathing, and often snoring, which would likely warn away any spiders. If a spider did crawl or fall into a sleeping person’s mouth, it would probably crawl back out again.
You Would Wake Up From a Spider in Your Mouth
Sleep is broken down into four stages, each of which has specific characteristics that make it unlikely a person would unknowingly swallow a spider. Sleepers tend to swallow much less during deep sleep and rapid eye movement (REM) sleep, providing fewer opportunities to swallow spiders. Although people do occasionally swallow during light sleep, this is a period of relative alertness. It is implausible that someone would stay asleep if a spider crawled on their face during this time, let alone into their mouth.
Your Mouth Is Not a Target
Studies show that less than one-quarter of people regularly breathe through their mouth during sleep. The majority of people therefore close their mouth while sleeping, making it extremely difficult for a spider to find its way inside.
Why Do People Think We Swallow Spiders During Sleep?
Although most people have heard the myth about swallowing spiders during sleep, it is unclear where this belief originated. The modern popularity of the myth may spring from a 1999 list of trivia facts in The Guardian, which claimed that throughout their lifetime, people swallow eight spiders during sleep.
Experts use the spider-swallowing myth as a prime example of why people sometimes believe things that are not true. The systems people use to sort out fact from fiction include a bias to believe in new information, a willingness to believe stories that appear logical, and a tendency to use potentially erroneous prior knowledge when analyzing new information. Although generally effective, these systems also set people up to occasionally believe in myths like this one.
Arachnophobia — the extreme fear of spiders — is one of the most common phobias, and evidence suggests that the potential to be afraid of spiders may be ingrained from birth. Given how many people find spiders creepy or crawly, the idea of swallowing them while you sleep makes for exactly the sort of alarming fallacy that can easily turn into an urban legend.
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