A woman in Russia found a small lump on her face, and what it turned out to be will leave all hypochondriacs shaking.

After spending some time in a rural area of Russia outside Moscow, the 32-year-old noticed a small, mysterious lump underneath her eye. It was slightly itchy, but otherwise seemed like nothing to worry about.

What happened next will quite literally make your skin crawl – within a few days, the lump had moved above her eye. From there, it made its way to her upper lip. Unsurprisingly, she went to the doctor – but not before taking some selfies to document the lump’s movement.

Kind of horrifyingly, the lump turned out to be a parasitic worm living under the skin on her face. The worm, which goes by the catchy name of Dirofilaria repens, is spread by mosquito bites, which she reported suffering from on her trip.

Thankfully, the treatment was simple – the doctors removed the worm surgically, and the woman made a full recovery. A case report detailing her experience is published in The New England Journal of Medicine.  

Although it is rare for the parasite to infect humans – it naturally lives in dogs and other carnivores – there are definitely enough recorded cases to make you uncomfortable. In 2009, a German man ended up in hospital after five weeks of headaches and difficulties with speech and motor functions – symptoms usually associated with a stroke. A physical exam found a lump that had moved from his arm to the back of his hand, which turned out to be – you guessed it – a massive worm crawling around under his skin.

The most common symptom of a D. repens infection in humans is lumps on the body, or what researchers describe slightly gruesomely as “a feeling of 'crawling' under the skin”. In about 35 percent of cases, these lumps move around as the worm migrates through the tissue under your skin.

The bad news is that the number of human cases is increasing – and spreading. Between 1997 and 2012 the number of recorded cases increased from eight to over 200 per year, and people are being infected at higher and higher latitudes. However, luckily, these worms can almost never reproduce in humans, and all symptoms usually disappear quickly if the worm is removed – so if you’ve noticed any strange lumps moving around your body after a mosquito bite, you should probably get to a doctor.