This is a fact so horrific it would not sound like it is real: The parasite sucks its host’s blood from its tongue until it dies then replaces it and lives in its mouth for the rest of its life.
But in fact, tongue-eating lice are real and live in the mouths of fish – one of which was recently discovered by a student in South Africa.
Don Marx, 27, from Cape Town, was fishing near Cape Agulhas when he caught a 2.5kg carpenter and found the stowaway in his mouth.
Marx, who happens to study Marine Biology, has heard of fleas but never seen them in the wild – so he took pictures to document the moment.
But after he sent the photos to Professor Nico Smit, a Zoologist at North-West University, he was overjoyed to discover this particular species of tick that he has never been seen before.
“Being a marine scientist and catching fish from a young age, has made me see a lot of parasites that live on fish and sharks,” he said. “But I was really surprised when I opened the fish’s mouth and saw the blue-eyed alien with the mustache staring at me.”
This special species of tongue-eating mite uses only carpenter fish as its host and has not been discovered by scientists for years.
Tongue-eating lice have been known for decades, but it was only in recent years that extensive research into their life cycle and behavior began.
It is thought that all species of tongue-eating lice began their lives as male fleas, drifting through the sea and looking for fish to settle on.
Each tick species – with more than 280 identified so far – appears to target just one species of fish.
Once the flea finds a host fish, it will swim through the fish’s gills and settle there as if it were at home.
If the host fish doesn’t have another flea in its place, the new flea will enter the mouth and stick to the tongue.
Using its front paws, the tick cuts the blood vessels on the tongue and then gets food by drinking its blood.
During this time, the male flea will turn into a female – its body size increases several times along with its legs, which it uses to attach to the fish.
Meanwhile, his eyes would shrink as he no longer needed to navigate.
When the fish’s tongue eventually dies and falls off due to lack of blood, the tick will attach itself to the tongue stump and effectively replace it.
According to a 1983 research paper, ticks ‘replace the mechanical function of the tongue’ by helping the fish hold its prey on the roof of its mouth while it eats.
It is the only parasite species that completely replaces the function of organs in its host.
The parasites will then live in the fish’s mouth for the rest of their lives, feeding on the fish’s blood and mucus, but otherwise causing no other harm.
If a tick that arrives at a host fish finds that a female louse is present, it will settle down as a smaller male and attach to the fish’s gills instead.
The male lives his entire life inside the gills, sometimes breeding with the female lice inside the fish, producing offspring that are expelled through the gills after birth to find a host on their own.
The fish may host several males as well as females, and in these fish, they are usually low in body weight – possibly because some parasites feed on their blood.
During laboratory studies, fleas were seen leaving the fish’s mouth only when the fish was dead, often sticking to the outside of its head or body.
However, it is not known exactly what will happen to the tick if its host dies in the wild.
Most likely, as with most parasitic species, the death of the host equals the death of the parasite living within it.