The creepy-crawlies. The heeby-jeebies. Makes my skin crawl. Many of us have these reactions when we see spiders:
Logically we know that spiders are unlikely to hurt us - in fact we can kill them quite easily - and that spiders are important parts of the ecosystem. Illogically we fear them and may be gripped with an illusory sensation that they are crawling upon us...producing itching that is very real. Why is this?
Some suggest that we may be evolutionarily wired to notice spiders and perceive them as a threat. New and German (2015) asked undergraduate students to perform a perceptual task: indicate if two crossed lines were equal or unequal in size each time they were briefly flashed on a screen. For most of the trials all that appeared on the screen were two lines in a cross shape, but for one trial another image was sneaked in next to the cross. This other image was either: a spider or a spider-like shape; a housefly or a fly-like shape; a hypodermic needle or a shape that was similar to a hypodermic needle. This is an "inattentional blindness" test because the participants have not been instructed to look for these things: their attention has only been directed to the lines so they should be "blind" or not notice other things. If participants do notice the other images, we can know that those images really stood out to grab their attention.
New and German found that the participants were much more likely to notice the spider or spider-like shapes than the other options. This was true even of participants who reported low fear of spiders and participants who reported high fear of needles. The authors believe that this represents an evolutionary wariness of spiders that has been passed down from our earliest ancestors in Africa where venomous spiders likely posed daily threats. In our modern world we are more likely to feel pain from an injection than truly be at risk from a dangerous spider bite - yet, spiders grab our attention more than needles.
If spiders grab our attention and make our skin crawl, when are we most likely to start scratching that imaginary itch? Llyod, Hall, Hall, and McGlone (2012) showed female undergraduates images related to itching, such as insects and skin rashes, and itch-neutral images, such as flying birds. As predicted, when participants viewed the itch-related images their self-reported levels of itchiness were significantly higher.
In addition to the self-reports, Lloyd et al. observed the participants' own scratching behavior and noted any scratching movement that lasted for more than one second. Out of all of the itch-related images, the photographs that included a person scratching him- or herself were associated with the most scratching from the participants. The authors suggest that feeling itch may be automatic but a scratching response may be triggered by a social situation that activates mirror neurons: brain cells that react the same to doing or watching a behavior.
When we put this all together, we know that your eyes are likely to be drawn to this guy if he is hanging out in your living room:
If your skin starts to crawl, you are normal: seeing insects and spiders makes us feel itchy. But you are most likely to scratch if you see your friends start scratching.
Further reading:
The New and German (2015) article is published in the journal Evolution and Human Behavior but is available online in draft form; the Lloyd et al. (2012) article can be accessed through your local college library.
Some individuals suffer from chronic, not just creepy-crawlies-induced itching. You can read more about recent findings related to this debilitating condition in this National Institute of Health article.
If you are thoroughly creeped out and itchy from reading this post, here is a totally unrelated video of a baby laughing to cleanse your palate. You are welcome.
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