Fact check: False claim that morning sleep crust is caused by 'male spider milk'

The claim: Sticky eye gunk is caused by 'male spider milk'

Arachnids are becoming a topic of misinformation on Facebook.

The Facebook page Horror Zone shared an image on Sept. 6 of a spider with the caption, "Its spider mating season and its a well known fact that at night male spiders mistake eyelashes for female spiders and thats why in the mornings we sometimes wake up with our eyelashes stuck together or a grittyness in the corner of our eyes, its all due to male spider milk."

The post generated about 5,800 shares and 2,000 comments in a week. 

But the claim is false. Experts say the gritty or waxy gunk in our eyes when we wake in the morning – sometimes called morning sleep crust – is not caused by "male spider milk."

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USA TODAY reached out to the page for comment.

Glands in eyelids release meibum

The crust that people find in their eyes when they wake in the morning comes from glands in the eyelids that release an oily substance called meibum, said Vicente Diaz, an assistant professor of ophthalmology and visual science at Yale School of Medicine.

When a person sleeps, the meibum dries up and becomes crusty so that when people wake up in the morning, they find their eyelids sticking together with a gritty feeling, Diaz said. The dried meibum is like wax.

"As it (meibum) hardens, it can make it hard for the eyelids to open in the morning, to make them feel stuck together," Diaz said. "As people sleep and they're not moving their eyelids, it kind of dries up that way."

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Occasionally, people can have an infestation of a tiny parasitic mite called Demodex louse on their eyelashes, which can leave a flaky substance called scurf and cause serious inflammation, Diaz said.

But there is no evidence that male spiders mistake human eyelashes for female spiders. 

The process of inseminating a female spider involves a complicated interaction of intricately structured body parts, said Rod Crawford, curatorial associate and a member of the arachnology & entomology team at the Burke Museum. It couldn't happen with an eyelash.

"Most importantly, male spiders detect the right female to mate with by contact pheromones," Crawford said. "Not something they are going to find on a human eyelash."

And "male spider milk" likely is in reference to a behavior seen in some species of spiders in which the male extracts the sperm fluid of a previous male from the genital openings of the female and then drinks it, according to Jerome Rovner, professor emeritus of biological sciences at Ohio University.

"It's as if he is 'milking' the fluid from the female," Rovner said. "He then inserts his own sperm fluid, which will be the basis for fertilization of that female's eggs, instead of the sperm of the previous male who had mated with that female."

There is no known "male spider milk."

Our rating: False

Based on our research, we rate FALSE the claim that morning sleep crust is caused by "male spider milk." Sleep crust is caused when meibum released by glands in the eyelids dries in the eyes as we sleep, causing a gritty feeling in the morning.

• Dr. Vicente Diaz, Sept. 9, Phone exchange with USA TODAY
• Dr. Scott Barron, Sept. 9, Phone exchange with USA TODAY
• Jerome Rovner, Sept. 10, Email exchange with USA TODAY
• Rod Crawford, Sept. 10, Email exchange with USA TODAY

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