Well, after asking Would mermaids be affected by tongue-eating lice evolving alongside them?, I realized they would be a worthy addition to a more monstrous subspecies of mermaid. There's only one problem: why?

As in, why would mermaids allow these parasites to replace their tongue? What possible benefits would make this worth it? In the linked question above, Mel suggested the lice could supply antitoxins or a greater vocal range, while Michael suggested the parasite could supply teeth and a tongue to infected mermaids, but I'm not sure how viable either of those are, and I don't know how to find out, ergo I am asking this.

In other words, my question is What Benefits Could Tongue-eating Lice Have For Mermaids?


  1. Yes, I am aware that these parasites could be given a place in a mermaid's body simply because of societal/cultural/traditional reasons, but that just doesn't seem to cut it for me. As far as I am aware, humans (and therefore mermaids) need justification to do something as drastic as allow a parasite to kill, eat, and replace a useful (if not vital) organ. TL;DR: The best answer will account for the pros and cons of this unusual organism and explain what benefits it could logically have that would enable symbiosis with its host, therefore rendering it not a parasite but a symbiotic organism.

  2. There is magic in my world, so one can use magical abilities as benefits in one's answer, as long as those magical abilities have a logical basis that is aptly explained. If this sounds like science-based magic, which is frowned upon, so be it. I prefer magic that makes sense (ie. that has a logical foundation) over the chaotic nonsense usually found in fantasy.

Final Note: If you need to vote-down or VTC, please explain why so I can improve the question. Thank you!

  • $\begingroup$ This already had -1 vote at 3 views before I upvoted it. I guess someone was just horrified at the concept... $\endgroup$
    Sep 12, 2021 at 0:02
  • $\begingroup$ @KEY_ABRADE No it just looks too opinion based, and werent we decided that hands wins, why ask at all, lol $\endgroup$
    – MolbOrg
    Sep 12, 2021 at 1:35
  • $\begingroup$ @MolbOrg: hands win, sure. But monster mermaids need creepy crustaceous tongues like pirates need hooks and eyepatches. As for being too opinion based, I'm open to suggestions to fix that. $\endgroup$
    – Alendyias
    Sep 12, 2021 at 2:04
  • $\begingroup$ I have possibly a new take on this. Are you still accepting answers? $\endgroup$
    – Mermaker
    Oct 28, 2021 at 10:37
  • $\begingroup$ @Mermakers: yes, I will still accept answers, thanks for asking! I really appreciate when someone adds to the idea pool, and I know people rarely respond to 'accepted answer' questions, so kudos for that as well! $\endgroup$
    – Alendyias
    Oct 28, 2021 at 13:47

3 Answers 3


This looks can be a mutualistic relationship of the service-resource type, facultative for mermaids (i.e. they don't need the parasite to survive)

  • The parasite can't hunt or feed itself, so it depends on the mermaid to get food (the resource)
  • After the tongue is replaced, the parasite gives the mermaid her hypnotic voice (the service)

The consequences

  • Regular mermaids don't have their signature voice, and they tend to not venture in the open wide world
  • A monster mermaid (with the parasite) has hypnotic voice and possibly needs to eat more to compensate for the parasite or have different dietary requirements than a regular mermaid, so those are the ones your explorers / adventurers are more likely to see
  • Up to you: the relationship between the "regular" mermaids and "monster" mermaids - do the regular mermaids consider the monster mermaids uncivilized degenerates that allowed themselves to be degraded by a parasite? A form of exile? Or is acquiring the parasite a rite of passage, making the "monster" mermaid an adult?
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    $\begingroup$ Very interesting, thank you! I have to ask, though, how could a parasitic crustacean give a mermaid a hypnotic voice? I love the idea, I just don't see how it could be accomplished. $\endgroup$
    – Alendyias
    Sep 13, 2021 at 23:12
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    $\begingroup$ @Alendyias maybe they have special organs like a cicada's Tynbal that allows them to produce very loud, very specific sound, the frequencies of which end up stimulating the reward mechanisms of the brain (basically the song both feels very good and hits like that one song you heard and absolutely loved at first), mixed in with other psychological effects that draw prey near. $\endgroup$ Sep 13, 2021 at 23:31
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    $\begingroup$ and @Alendyias you stated that magic is allowed, so why not make that the magic of these parasites? $\endgroup$ Nov 2, 2021 at 21:33
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    $\begingroup$ Have a +100! Very good answer! $\endgroup$
    – Mermaker
    Nov 4, 2021 at 18:54
  • $\begingroup$ @ArtickokeAndAnchovyPizzaMonica: good question! All considering, I believe I will do just that. Thanks for the suggestion! $\endgroup$
    – Alendyias
    Nov 5, 2021 at 22:03

They enable Parthenogenesis.

Monstrous mermaids have a hard time finding sexy sailors to mate with - either because of how they look, or their fame as men-eating monsters. Maybe its their size, or even their biology - even if male humans could mate with them for the fun of the couple, that pairing by itself doesn't produce viable offspring.

Enter the tongue-eating lice.

The lice itself doesn't bring that many mechanical benefits for the monster-mermaid. It replaces their tongue and make them a little bit more monstrous, even. But the lice pumps them with special substances that, when introduced to their bloodstream, enables them to get pregnant and give birth without needing a male - as it happens in some parts of nature already with different pairs of host-parasite..

Thus, the lice-enabled mermaids are able to survive without needing mates. They can still bring sailors to their lairs and do evil things with them, mind you, but they don't need their man-juices to continue their species. They probably just want to eat them, since their babies will come no matter what.

This creates a terrifying setup for your world, with the opportunity for exciting reveals - a sailor going for a kiss and finding out not the inviting tongue of a mermaid that wants to get frisky, but the parasitic lice of the fish-woman that is about to eat him alive can make for an awesome campfire tale inside your world, for example.

So, the lice.

A mermaid that gets the lice gets the ability to reproduce without any external help. This enables them to shun their sailor-loving cousins, retreat deeper into the seas and, over time, become more and more like a monstrous sect of murdering-sea-witches. The lice, for them, isn't only a cultural marker of their tribe, but also a tool for survival. It's how they "free themselves" of the two-legged dryskins, keeping their race "pure", without external "interference" or "contamination".

Give them some extra magical abilities to booth, caused not by their lice but by the focus they give to magical learning, and you can get a truly terrifying foe for your heroes.

  • $\begingroup$ Very interesting, thank you! This would definitely add some nice flavor to my setting, and I do enjoy the idea of having a relatively isolated race to work with.... $\endgroup$
    – Alendyias
    Oct 28, 2021 at 14:44

They're instruments of torture for a despotic regime. The equivalent of cutting out tongues above the surface... the sort of thing you do when you're unhappy with what the victim is saying. But it's so much more than that too. A man who was victim to this (supposing he survives) might still give his kids a peck on the cheek for affection (hopefully a long distance away from where the mutilation took place). But who would allow that if there's a monster in the guy's mouth?

You can feel it moving around on its own. It doesn't obey you. When it's hungry, it clamps down, and the nerves are always raw. And it's always hungry.

You can't eat in the presence of others, lest they glimpse it. You're mute. You're forever outcast.

Most, I think, would soon become insane. Those who don't suicidally depressed. Can it even be removed safely without modern medical intervention?

Now, this isn't a benefit to those who would suffer from the thing. But it is to the benefit of those who wish to be cruel, to punish, and to torture. Presumably other merfolk.


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