The candiru catfish has something of a slippery reputation. As legend tells it, should someone stop to urinate in the freshwaters that surround South America’s rainforests, they might find themselves with a “toothpick fish” stuck up their urethra. While the legitimacy of such accounts seems shaky at best, some candirus have found other ways to burrow inside humans.

Also known as vampire candirus owing to their thirst for blood, they will swim into fishes’ gills and latch onto major blood vessels to feed – which is the behavior alleged to have motivated them to swim up small gaps of all varieties. While urethras are a stretch, a 2021 case study published in the Journal of the Brazilian Society of Tropical Medicine reveals the brutal way one “human-biting candiru” latched onto a person’s skin as a means of getting a bellyful of blood.

“The human-biting candiru from the subfamily Vandelliinae, a part of a scientifically undescribed genus and species, fastened to the back of a boy,” reads a photo caption from the article.

“Upon a forceful removal, the fish’s mouth leaves a bleeding [oval] lesion at the attachment point. Note the candiru’s abdomen full of blood, its strong hold on the victim, and another bite to the right of the bleeding one.”

The following image contains blood, proceed with caution.

While candiru catfishes biting humans is rare, it’s not unheard of. Living humans are usually off the menu for most of these fish, but corpses are a different matter. Carrion-eating whale candirus will gorge on the carcasses of river dolphins and other dead animals – including us – but two species take different approaches. 

Cetopsis candiru will bite into a carcass and essentially twirl, creating a neat tunnel into the tissue which it can use to enter the body cavity and eat it from the inside out. These fish will swarm, sometimes in their hundreds, in feeding frenzies.

The candiru Ceptosis coecutiens takes an alternative approach, making rapid bites and rips to tear off chunks before coming back in for another bite. Both fish have been reported feeding on human corpses, and their bites are so strong that they have left circular marks on skull bones.

However, reports of attacks by the as-of-yet undescribed “human-biting candiru,” as the authors call it, show that some of these fish appear to have a taste for our blood, too. Using specialized teeth, they can latch onto human skin and hold on with strong head muscles which make them difficult to remove while they’re feeding on blood.

While most reports of candiru fishes’ more intimate attacks on humans seem to be built on myth, it seems the human-biting candiru has other ideas.