In "The X-Files" season 5, episode 19," "Folie à Deux," a vinyl siding salesman named Gary (Brian Markinson) is convinced that his boss (John Apicella) is a gigantic malevolent insect in disguise. Gary hears little chirps from his cubicle, and occasionally catches a glimpse of what his boss really looks like. Because this is "The X-Files," the audience can't be sure whether Gary is hallucinating, or if the insect really is a supernatural being of some kind. But we can be sure that Gary's delusion — or perhaps the insectoid conspiracy — deepens when his co-worker goes into their boss' office and emerges as a white-eyed zombie. Gary explains that these monsters are "hiding in the light," and doesn't understand why only he can see them.

Gary's use of the phrase attracts the attention of FBI agents and paranormal investigators Mulder and Scully (David Duchovny and Gillian Anderson), who are intrigued by the connection to another mass shooting. (That crime took place at a church where the pastor was convinced that one of his congregants was evil.) Mulder and Scully will end up becoming negotiators after Gary takes his office hostage, hoping to expose the insect among them. During the negotiation, Mulder will also see Gary's boss as a giant insect monster — albeit very briefly and with the lights turned off.

The always open-minded Mulder begins investigating Gary's boss, convinced that he is some sort of malevolent monster. The man appears to Mulder as a monster several times, and Mulder is eventually committed to a psychiatric facility after threatening to shoot him/it in front of his boss, FBI assistant director Skinner (Mitch Pileggi). By the end of the episode, Mulder will be driven to the brink of insanity by an insect only he can see and hear.

In the episode's epilogue, Scully admits that she too saw the insect. But she chalks up the incident to a phenomenon known as Folie à Deux — literally, "madness for two" — wherein two people appear to share a psychosis.

Shared Psychiatric Disorder

Folie à deux is an actual documented psychiatric condition with the clinical name of Shared Psychotic Disorder (DSM—IV–297.3). It's not the same as parasitic manipulation, akin to what we'd call "gaslighting." Nor is it the same as mass psychosis, which is a more frenzied form of groupthink. Shared Psychotic Disorder is a phenomenon where two people, often stuck together in close quarters with little exposure from the outside world, begin to share common delusions and even hallucinations. The 1996 Tracy Letts play "Bug" and its subsequent 2006 film adaptation by William Friedkin are explicitly about the phenomenon.

SPD is often marked by a "dominant" personality who brings an existing delusion into a shared scenario, and a "submissive" personality who absorbs it and shares it. And while it doesn't necessarily involve hallucinations (i.e., imagining your boss is a giant evil bug), they can be part of the delusion. Rampant paranoia seems to be the most common symptom of SPD: One recorded case involved a woman who became convinced her food was poisoned, and who spread that paranoia to her adult daughter. The two nearly starved themselves and the adult daughter's young son, who they tortured by denying the boy food. SPD is also not restricted to two people, and can be referred to as folie à trois, folie à quatre, and so on.

A group of people are locked together in a room and all start to believe weird, paranoid conspiracy theories. Where have I heard that before? Perhaps, given the shared isolation of social media, Reddit, and the like, more studies should be made into folie à deux becoming a folie à masses.

What Is The Cause?

The cause of SPD is not known. It's tempting to tie it to the abstract notion of human willpower, but that's hardly scientific. It's been observed, and it's been treated. But there is, as of this writing, no scientific origin for SPD.

It's highly likely that "Folie à Deux" writer Vince Gilligan knew about the unknown origin of SPD, and spun that uncertainly through a scientific loophole into creepy supernatural fiction. The insect conspiracy in "Folie à Deux" is far-fetched — insects only grow to that size in Guillermo del Toro movies. But, like many paranoid delusions, it actually has a toehold in reality. Researchers have discovered insects that come armed with mind control venom they use as a self-defense measure, and the idea of being injected with such a substance is just scary enough to inflame the imagination.

But don't fear, dear reader: Your boss is not a giant insect. "They" are not injecting you with mind-control venom. And "they" are not hell-bent on taking over your mind. Giant insects have better things to do with their time.

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