The philacry are humans with wings like dragonflies, crystal clear and barely weighing anything, yet able to withstand the rapid wingbeats of flight. Though they can fly from childhood, buzzing about with some of the dexterity of dragonflies, this takes a lot of energy, and a lot of oxygen, leading to the same respiratory system that birds have.

The question I have, is where could you store air sacs in a mostly human body? Birds have nine air-sacs, but maybe philacry could manage with less? I guess it's possible to have less of them and make them larger.

I didn't want to shrink too many organs, so I wondered if I should lengthen the torso. Or, maybe you could put them in the buttocks, and make them literal balloon butts? I was considering putting them in the chest, so that the philacry were mistaken as an all female race like harpies, when really it would just be moobs. That's my thought process ATM.

Question: Where could I put air sacs in a human body?

Further details would be how many we could put in, and how large they would be.

Thank you so much!

  • $\begingroup$ I'm tempted to up-vote just for "balloon buts", but actually it raises interesting bio-mechanical issues too. If someone doesn't get there first, I have something. $\endgroup$ Jan 28, 2021 at 0:50
  • $\begingroup$ @Tantalus'touch. lol! Glad you liked it! Im seriously considering that adaptation, though I don't know how sturdy the airsacs could be. It'd be a problem if someone smacking your ass could be fatal! Would a burst air-sac be fatal? Do they heal? but maybe there's enough fat and muscle to protect them? Either way, I can imagine songs using that idea. $\endgroup$ Jan 28, 2021 at 1:08
  • $\begingroup$ when we exercise the lung literally breathe out "fat" following this logic that fat = CO2 then it will be the belly for male and balloon butts for female ;D $\endgroup$
    – user6760
    Jan 28, 2021 at 1:53
  • $\begingroup$ @user6760 I guess we could store the air sacs in the fatty parts of the body? Guys have a lot more belly fat, don't they, so you could give them something behind their lovehandles. But would distance from the lungs or ribcages be a problem?? Like, could your tits have air sacs, or would ribs get in the way of that? And would bubble butts be troubled by the distance from the lungs to the booty? So many questions x3 $\endgroup$ Jan 28, 2021 at 2:20

2 Answers 2


In the vertebrae

This is where most bird (and dinosaur) air sacs are located, forming special pneumatic cavities in the sides of the vertebrae. It should be noted that several bird air sacs do not actually invade the vertebrae, they just sit in the thoracic cavity.

  • 1
    $\begingroup$ Oh, neat! Makes me wonder if they can protect your spine. $\endgroup$ Jan 28, 2021 at 10:21

I guess that whenever you place them you don't want to mess up too much with the center of gravity of the flying body.

If the wings are located where our shoulder blades are, the center of lift will be somewhere around there. Considering that usually the CoG is located somewhere in the abdomen, the creature ends up with a heavy rear, which is a configuration avoided like a stinky skunk by any aircraft designer, because it makes stalls impossible to recover.

A suitable location to lighten the rear is therefore anywhere from the belly down. Buttocks seem to indeed be a good choice, considering that the legs can be kept folded during flight. If not, legs are also a convenient location.

  • $\begingroup$ Hey Dutch! wanted to say that's a really cool avatar! With a heavy rear, will the air sacs really make it lighter? I guess they will if we remove some muscle and fat?? Having air sacs in the legs is neat, give the philacry thick thighs xD. $\endgroup$ Jan 28, 2021 at 10:18
  • $\begingroup$ @ArchduchessFerdinand, considering that the lungs are already pretty light, putting more air in the back will necessarily shift the CoG toward the head. Even better if some fat/muscles are made thinner. $\endgroup$
    – L.Dutch
    Jan 28, 2021 at 10:40
  • $\begingroup$ @ArchduchessFerdinand glad you like the avatar ;) $\endgroup$
    – L.Dutch
    Jan 28, 2021 at 10:43

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