If seeing a mere photo of a spider sends a shudder through your spine, you’re not alone. Arachnophobia (fear of spiders) is one of the more common phobias, and Western society seems to have a collective aversion to all things creepy-crawly—from insects like cockroaches and silverfish to myriapods like centipedes and millipedes. While some of these spineless characters can poison us or spread disease, you can usually take out your opponent with one well-placed swat or stomp. So why do they often evoke terror?

Survival of the Anxious

One theory of evolutionary psychology holds that our anxious ancestors had a better chance at survival than their intrepid counterparts. Someone who sticks their head into a bee nest while hunting for honey, for example, might not live to tell the tale—or produce any offspring to inherit their ill-advised audacity. Those who approach warily, on the other hand, may walk away unscathed and go on to procreate with other cautious people. Over millions of years, humans may have evolved a predisposition for anxiety towards bees, spiders, and other threatening organisms that we colloquially refer to as “bugs.” (Scientifically speaking, true bugs are species of insects in the order Hemiptera.)

“Of course, there's no ‘fear bees' gene,” Dr. Jeffrey Lockwood, an entomologist and the author of The Infested Mind: Why Humans Fear, Loathe, and Love Insects, tells Mental Floss. “But there is evidence that we are particularly prone to associate certain stimuli with danger in the form of ‘prepared learning’—not unlike how we readily learn language.”

What bugs lack in size they make up for with other qualities that, as Lockwood puts it, “push plenty of our fear and disgust buttons.” Their small stature allows them to infiltrate both our bodies and living spaces, and they’re capable of avoiding our swats and stomps with fast, erratic skittering (or flight). And although many can’t poison us to death—fewer than 30 of more than 43,000 spider species have been known to kill humans, for example—some, like cockroaches, pose other dangers.

"It's mine now."HAYKIRDI/iStock via Getty Images

“Because [cockroaches] feed on human feces as well as human food, they can spread germs that cause disease,” the World Health Organization reports [PDF]. “In addition, they carry the eggs of parasitic worms and may cause allergic reactions including dermatitis, itching, swelling of the eyelids, and more serious respiratory conditions.”

When it comes to injury, allergy, or disease, an innate sense of ‘better safe than sorry’ could help explain why some of us jump when we see any slight movement that might turn out to be a bug. There’s no significant downside to mistaking a tumbleweed for a spider, or even mistaking a harmless spider for a deadly one.

Creepshows of All Kinds

There is, however, a difference between simply thinking bugs are gross and actually fearing them.

“You can tell if someone’s bug-phobic if they check for bugs, freak out around bugs, or avoid bugs at all costs,” Dr. Jenny Yip, a licensed psychologist and the founder of the Renewed Freedom Center of Los Angeles, tells Mental Floss.

If you scan the nooks and crannies whenever you enter a room to make sure you don’t spot a many-legged guest, you might have entomophobia (fear of insects). Sometimes, the leap from “I’m creeped out by bugs” to “I’m scared of bugs” occurs because you had a bad experience with a bug, or you learned—by direct teaching or just by observation—to fear them.

“Perhaps your great-grandmother was badly stung, and she forcefully taught your mother that bees are terrible creatures capable of dispensing death,” Lockwood says. “Unless your mother had some good evidence [or] experience to override this parental message, she likely grew into a fearful adult. And when she had you, it would seem quite likely that she'd transmit this fearful message ... and so on.”

As Lockwood explains in The Infested Mind, media and entertainment franchises transmit fearful messages about bugs, too. Apart from butterflies, ladybugs, and a precious few others that we deem harmless, fascinating, useful, and/or beautiful, most bugs get a bad rap on screen. Between NBC’s Fear Factor, less-than-subtle films like 1990’s Arachnophobia, and all the innovative advertisements for pest control, our revulsion is continually reinforced.

These representations reflect a Western societal shift from earlier, rural communities that could differentiate between dangerous and beneficial bugs—and even valued some as food sources—to current, urban communities that are obsessed with cleanliness. “Disease, including insect-borne disease, took a serious toll on Western societies for centuries. So, we generalize that any insect is filthy—and living in cities, there's not much of a downside for making ‘false positive’ determinations of this sort,” Lockwood says.

Facing Your Fears

But avoiding all bugs isn’t a productive way to deal with a phobia; in fact, you could end up accidentally expanding it. “Over time, a fear of spiders, for example, can be generalized to other bugs, like flying insects,” Yip explains. Instead, she recommends exposure therapy, where you encounter the bug in a very hands-off way and work up to confronting it directly.

“Start by looking at pictures of bugs, watch videos of bugs, go to places where bugs could be, interact with a toy bug, and then eventually, you actually interact with the real bug,” Yip says.

If you want to get rid of your bug phobia, a clinical psychologist can help you set up a similar progression. And if you don’t exactly fear bugs, but would still like to dispense with your bad feelings towards them, you could always choose a bug-positive film for your next movie night—say, A Bug’s Life (1998) or James and the Giant Peach (1996).