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I've been thinking of reviving an old Fantasy idea of mine, and I recently came across a description of a group of mythological beings that piqued my interest, and which would actually fill a niche I had been looking to fill in the World I'm working on: the "Astomi", a tribe or race of Mouthless Humanoids described in the works of Pliny the Elder.

I had already considered having a group of people with no visible mouth, and the description of the Astomi "living on scent" and being "covered with thick hairs" gave me an idea of a mechanism by which they might be able to feed themselves, which also derives some inspiration from mythological figures such as the Futakuchi-Onna and Harionago from Japan, both of whom can control their Hair as an alternative means of Feeding or Attack/Defense, and from real-life filter-feeding Polychaete Worms, many of which use hair-like filaments/cilia to catch and feed off of particulate from the surrounding water (or occasionally Larger Prey Items). These usually have small tentacles or other "hair-like" structures that pull food towards specialized Mouths that are often invisible to the naked eye.

My question is... Would this work for a larger terrestrial animal? I'm not sure how much organic particulate could be strained from the air as opposed to the water, or if it would be enough to sustain something human-sized, but I do like the idea of their means of feeding being more or less Invisible, and connected to their "hairy" appearance... How much hand-waving do you think I'd have to do for this to work?

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    $\begingroup$ Maybe baleens? In this case they would have a mouth, of course, but it would be covered by this fur-like filter, which wouldn't be discernable from the fur covering the remaining of the body, seen from outside. They would feed themselves filtering the mud or the water and could sustain a human-sized mammal (considering that they can sustain a whale) $\endgroup$ – McTroopers Jan 8 at 23:21
  • $\begingroup$ Hmmm, could be interesting... Maybe the skin covering what used to be their mouths is fully or semi-permeable, allowing them to strain that way?? My idea was that they were originally Normal Humans that Lost Their Mouths because they were cursed/punished for not Speaking Up in the face of a Great Atrocity, but it's possible that just means that they can't speak anymore, and that there's some outward indicator of this? $\endgroup$ – BonnetBee Jan 8 at 23:27
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    $\begingroup$ Ultimately it will depend on the environment that the creature lives in rather than the design of the creature itself. See Which conditions would make aerial filter feeding successful? and An environment where a bird-like creature can survive on passive feeding. $\endgroup$ – Mike Nichols Jan 8 at 23:32
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Possibly, but not by living on nice smells

Let us assume that the Astomi have energy requirements comparable to humans. Looking at the Food energy article in Wikipedia:

According to the Food and Agriculture Organization of the United Nations, the average minimum energy requirement per person per day is about 7,500 kJ

Looking at the energy-dense foods in my pantry, Nutella's nutrition information label says that it has 2228kJ per 100g. So, if sufficient atomised Nutella is being sprayed into the atmosphere where the Astomi live, they are viable if they can absorb about 330g each day. Unfortunately, naturally occurring sprays of atomised Nutella are not a feature of even the most friendly fantasy world, so an alternative food source will be required, but this gives an idea of the minimum mass required.

Note that a large proportion of human energy is expended on running the brain and/or regulating the body's temperature - by making the Astomi cold-blooded and or small-brained they will require significantly less energy. On the other hand, if you want them to have greater-than-human capabilities then they will require a larger energy budget.

Can they live on smells?

At this point a quick thought experiment is in order. Imagine that there is a 4m x 4m enclosed room divided up into a grid of 1m x 1m squares, with one Astomi sitting in each square, for a total of 16 Astomi. (Assume a ceiling height of 2-3m.) Now imagine that 1g of strong perfume is sprayed into the air in this room every 15 minutes for 24 hours - this is a lot of perfume, resulting in a room that would be absolutely reeking by the end of the experiment. However, this is still only 96g of perfume between 16 Astomi - even if the Astomi absorb every single molecule of the perfume they have only received 6g of nutrition each. The perfume would need to have an energy density more than 50 times that of Nutella in order to provide adequate nutrition. So odours (pleasant or otherwise) are not going to cut it, the Astomi definitely need something more substantial.

Possible sources of nutrition

Given the requirement for feeding to be invisible to the naked eye, a few options, possibly used in combination, are:

  • pollen: The Astomi brush past flowering plants and catch the pollen on their hairs, subsequently absorbing it. They will need to brush past a lot of flowers in order to survive this way given the low pollen mass per flower, which will mean they have a higher energy budget and will need to be nomadic in order to give the flowers in an area time to recover before they feed again.
  • insects: Possibly Pliny the Elder had it backwards and the Astomi actually emit smells that attract insects. The hairs then trap the insects and draw them into tiny pockets hidden beneath their hair akin to the pitfall traps of pitcher plants, where they are digested and the nutrients absorbed. A variant of this would make the Astomi anteaters - they sit or kneel down on an ant nest and appear to a surface observer to be sniffing the air, while below the surface the specialised long hairs on their buttocks or knees are diving into the ant nest to seize ants and larvae then drawing them into their digestive pockets.
  • Honey: The nutrition label on the tub of honey I am looking at says it has 1401kJ per 100g. So if the Astomi have hairs that can slip into a beehive and escape unscathed they can definitely do pretty well from a hive. However, this encounters the same issue as collecting the pollen themselves - they need to have a large range before the resource will regenerate.

In short, the Astomi are plausible insectivores, but not odourvores.

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    $\begingroup$ This is super cool! I'd had the thought Pliny Sr.'s theory about smell was based on the science of the time, and that the lack of prior observation/technology meant that there would be no way to discern the actual mechanism of their feeding, making it look like they carried things that smelled good to feed off the scent itself; the bit about city odors being hazardous to them would still hold true, as human activity might have polluted or defoliated the area, so the Astomi might have either been ingesting pollutants, or just couldn't find food at all; Your contributions seem to support this :3 $\endgroup$ – BonnetBee Jan 9 at 16:59
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    $\begingroup$ To take your honey theory a step further. It's a symbiotic relationship they have with the bees. When they approach the hive, they attract the bees with a nectar that they secret and a scent that pacifies the bees long enough for them to draw honey. The nectar they provide more than compensates the bees for the honey they take. $\endgroup$ – Richard U Jan 9 at 19:12

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