Follow-up from: Where to place breathing holes/spiracles on a bipedal humanoid

My humanoid bipedal species and other creatures sharing a common ancestor primarily breathe through spiracle-like breathing holes that are located close to the limbs, in the case of the humanoids on their chests enter image description here

In the previous question Gillgamesh rightfully pointed out one issue with the creature designs from Avatar, which was my starting point: How do they filter out debris, especially for the flying creatures?

enter image description here

For humans we have nose hair, but for strictly aesthetic reasons, I don't want to use that approach for my creatures, unless there's a way to hide those hairs from view unless one gets really, really close. I've looked at aircraft designed for takeoff from dirty airstrips for inspiration, but can't see how to adapt that for animals, especially the air inlets on top of the wings (which works for the flying creatures, I guess, but not the ones that don't fly). A sort of filtering system that's visible unless from up close seems the most sensible, but what could that look like?

Related, and a possible follow-up question, would hair or fur on the creatures 'work' with spiracle-like breathing holes? Would the area immediately surrounding the 'holes' need to be naked or could there be hair/fur right around it without issue? If there is a filter, I can't see why it wouldn't be possible, but I'm not sure, hence the question.


2 Answers 2


Bagless vacuum cleaners have had to solve this. At least some of them use two-step method: cyclone to separate coarse stuff and filters to remove fine-grain stuff.

The cyclone creates a vortex that pushes heavier particles outwards due to [pseudo] centrifugal force while air is sucked inwards from the center of the cyclone. Then the air is further filtered with two or more filters.

If your spiracles were pointing downwards, and the opening formed a vortex funnel (see example image), and the funnel was covered with mucus, the mucus would catch most of the coarse particles and lot of finer as well, and gravity would eliminate the mucus.

Then hair and mucus in the rest of the air ducts would filter out rest of the finer particles much like our respiratory system does.

  • $\begingroup$ Thanks a lot for the reply! That's what I'll be going with. Since I am very bad at visualising things, with spiracles pointing downwards and a vortex funnel as opening, do you mean something like #1 in this image that I threw together or more like #2 in the same link? The 'end' of the funnel would then be internal and lead to the lungs eventually? $\endgroup$ Commented Feb 3 at 15:24
  • $\begingroup$ @SaintDiabolus #2 is closer to what I had in mind. The cone orientation might need some work (not necessarily though), but it's all mere adjustments from there on. And yes, the 'end' of the funnel is internal, and leads to the lungs. $\endgroup$ Commented Feb 3 at 16:49
  • $\begingroup$ Awesome, I'll play around a little with the orientation and all. Thanks for the suggestion! $\endgroup$ Commented Feb 4 at 15:02

As far as I know, the spiracles of most insects are also surrounded and covered by very very fine hair.
Alternatively, it could be covered by a natural membrane or mucus like Gore-Tex, which is permeable(ish) to air but not water or debris. That might stretch belief a little far, though.


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