Should You Panic About ‘Parasitic Eye Worms’ Or Face Flies?

My second-worst experience thinking about insects in my eyes was a real-life encounter, when I jogged face-first into a cloud of gnats while running on a trail. I couldn’t shake the feeling that there was something still in my eye, and hours later I finally extracted a dead(?) gnat from the inner reaches of my eyelid with a Q-tip. The only thing that beats that: reading about face flies on Gizmodo yesterday.

Recently, a woman in California ran face-first into a bunch of flies on a trail, and discovered later that one of them had expelled worms into her eye. “She recalls swatting the flies from her face and spitting them out of her mouth,” the case report says. Over the next month, she and two ophthalmologists found a total of four worms in her eyes.

I want to be clear about one thing: face flies and eye worms are two different things, and they work together to produce this particular body horror. Face flies drink animals’ tears. Eye worms live inside the face flies’ faces, in their mouthparts, and escape into the eye when the face fly feeds. Every now and then, if a face fly happens upon a human eye, a person like you or me or the California trail runner can end up with an eye full of tiny worms.

The good news: this is really rare

There are several species of eye worms, and in part this recent case is newsworthy because this and another case reported last year were caused by a different species (Thelazia gulosa) than the ones that have previously been found in human eyes (Thelazia californiensis).

These worms mainly infect animals; when they find a human eye, it seems to be a mistake. The worms cannot breed in your eye, so even if you do get infected, they will not live there forever.

The take-home message for you and me is fairly simple: seek medical attention if your eyes are irritated and you don’t know why, or if you find, you know, worms in your eye. You can see a photo of a Thelazia worm on this CDC page. They are little bitty guys, like if you shrunk a noodle down to a size where it was almost, but not quite, invisible.

For the doctors out there, the authors of the recent case study recommend that eye worms be sent to a parasitology lab, to be identified not as “yep, that’s an eye worm” but down to the species level. Because the scientists are wondering if two cases in two years means that T. gulosa is becoming more common, and if so, we should really keep an eye (sorry) on that.