If you spot a tiny drain fly resting in the corner of your bathroom, and your first instinct is to swat it away with your bare hands, you might want to think twice.

According to Chinese media reports, a man in China had a drain fly land on his lower left eyelid. He casually swatted it away and instinctively rubbed his eye. Soon after, his eye became swollen and painful.

After seeking medical attention, he was diagnosed with seasonal conjunctivitis. But things quickly took a turn for the worse. 

His vision deteriorated rapidly, and he developed signs of a Pseudomonas aeruginosa infection — a type of bacteria that can cause infections in the blood, lungs and urinary tract.

The infection eventually caused severe tissue damage around his eye, leaving doctors with no choice but to remove his entire left eyeball.

According to reports, these small insects, commonly found on bathroom walls, near drains and around sinks, are known as drain flies or moth flies. While they may look harmless, they actually breed in damp, dirty areas with built-up grime, and can carry bacteria like E. coli, salmonella, and pseudomonas aeruginosa. 

The eyes are an ideal environment for bacteria to grow. 

A similar case reportedly involved an eight-year-old girl who vomited "live worms" for over a month. Despite visiting several hospitals and taking deworming medication, her condition did not improve.

Doctors eventually discovered she had a digestive tract infection caused by moth fly larvae. They believe water splashing from the sink or toilet carried the larvae onto her toothbrush, cup and other bathroom surfaces, which she unknowingly ingested while brushing her teeth.

According to ophthalmologist Li from Peking University People's Hospital, moth flies can also affect the eyes in two ways. They may fly directly into the eye, bringing bacteria and tiny body hairs with them, or they may be crushed with bare hands, leaving behind bacteria and debris that can be transferred into the eye if you rub it.

If a moth fly gets into your eye, experts recommend flushing it with artificial tears, saline solution or antibiotic eye drops. If those aren't available, use bottled water or cooled boiled water.

If the insect is on the white of the eye or the inner eyelid, wash your hands first before gently removing it with a clean cotton swab. If it's on the cornea, however, keep rinsing and avoid touching or rubbing your eye, as trying to remove it yourself could cause further injury.

If pain, redness, blurred vision or light sensitivity persists after rinsing, or if the insect cannot be removed, seek medical attention immediately.

TL;DR: Don't squash moth flies with your bare hands, and if one gets into your eye, rinse—don't rub.

Photos: SingTao Headline, WikiTok