I am working on a habitable planet that orbits around a red dwarf star and it is about 1.5 times bigger and more massive than the Earth. Gravity there is stronger and the atmosphere is thicker.

Now, one of the creatures that inhabits this planet is a large aerial predator that hunts above the savannas. It's a hexapod (six limbs), has two large pair of wings (the front pair being larger than the second) and small hind legs, large chest muscles, bony thin plates of armour from protection against radiation from the star, a relatively small head compared to the rest of its body, and a wingspan of 10 meters.

Is this creature possible? If it is what could explain why it reached such a large size? And if not what might I change in my world to make it possible?

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    $\begingroup$ Quetzalcoatlus had a bigger wingspan than that. What's the specific worldbuilding issue you need us to solve? Meantime, take the tour and read-up in the help center about how we work and - welcome to the forum. $\endgroup$ Nov 16, 2019 at 16:56
  • $\begingroup$ It's a little confusing because you ask how big a flying creature can be but you already said it has a 10m wingspan, so try to be specific about what the question is. Are you asking about its weight? Length? This is about twice the size of a pteranodon by the way. $\endgroup$
    – Vogon Poet
    Nov 17, 2019 at 0:04
  • $\begingroup$ If i may: have a look at e.g. how i structured my B.O.B. question(s) $\endgroup$
    – dot_Sp0T
    Nov 17, 2019 at 14:18
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    $\begingroup$ We can build helicopters and jets and so on which proves that there is no physical reason why large objects can't fly. Maybe alien muscles are stronger. It's unbelievable that they happen to be the same by random chance even though you want them to be different. applying earth's laws to other planets and then asking questions about how they can be different (just make them different) is among the top 10 world building mistakes I see people making here. $\endgroup$
    – Raditz_35
    Nov 17, 2019 at 16:07

3 Answers 3


Anticipatory TL;DR:

In order to have a large flying hexapod, you might want to consider adding:

  1. Flaps between limbs
  2. A habitat near some form of updraft - ocean winds, volcanic wind, or some manufactured thing.
  3. Honeycombed bones; an organ to create hydrogen
  4. An incredibly large diet; perhaps hibernation when this isn't possible

Dense atmospheres

Depending on how dense the atmosphere is, flying could end up being much more similar to swimming and accordingly, birds could become more similar to fish. Therefore they could grow to be large as long as they had light, maybe hollow bones and incredibly strong muscles. I’m not sure how dense the atmosphere you’re working with is, but if it becomes extremely thick the creatures that could fly could begin to deviate from what a traditional bird looks like: namely, they could become similar to a family of insects called the mymaridae, the species which comprise it which don’t have traditional wings but rather have limb-like extensions covered in bristles, and using that they can fly through the air as if they’re swimming: the Arescon and Myanmymar are examples of this.

Less dense atmospheres

If the atmosphere on your world isn’t that dense, then a solution would have to be worked out some other way: trying to figure out how to minimise the amount of lift that your aerial predator needs.

Since generally the larger an object is the more lift it needs - its mass growing as its length cubed and the surface area as its length squared - and therefore needs bigger wings in proportion to its body as it grows.

Of course, as the creature needs larger wings, the material that makes up the wing must also accordingly be stronger lest the wing collapse under its own weight.

As an example, Pterosaurs on Earth in prehistoric times were shaped like a kite: a relatively small main body, flat for aerodynamic reasons, with flaps of skin between limbs to increase surface area, and ginormous wings. Relatively recent hypotheses also suggest that these dinosaurs would live near coastal cliffs and jump off of these, relying on the ocean gusts to get them airborne - at which point they would mainly glide.

Following that, any creature with relatively small wings and large body mass would never be able to fly, and flapping their wings wouldn’t work.

Other misc issues; food consumption and internal structure

This issue was discussed and solved on an old Discovery Channel show called “Dragons: Myth Made Real”; in order to come up with a way for dragons to fly they determined that they must possess light yet durable honeycombed bones that were light but durable and an inflatable bladder that could be filled with hydrogen produced with bacteria in their stomachs (or perhaps they could have a separate organ specifically dedicated to the production and excretion of this hydrogen - or perhaps the organ could pump hydrogen into the honeycombed bones? The choices are endless… )

Further, birds must eat about ¼ to ½ of their weight in food each day; this assumes an average weight-to-wingspan ratio. However, as discussed above, this ratio must increase as the size and therefore mass does - I wouldn’t be surprised if your aerial predator had to consume upwards of 3/2 times its body mass each day if it flew all the time (and didn’t glide: if it were primarily a glider it might need to consume less). Therefore, in times when this mightn’t be feasible perhaps it would sleep - maybe even hibernating in winter when other things hibernate because it would be harder to find food.

Behaviour - I know you didn’t ask for this but I couldn’t help myself

If these predators act in packs and don’t live isolated lives (this might make more sense than an isolated life given how much food they need to eat - and also it would make them more of a formidable enemy) then perhaps it would function much like a pride of lions; the leader doesn’t need to expend energy hunting and instead the females and young members serve the food to the rest of these creatures.

On the other hand, the pack (maybe a phalanx? See https://www.backyardchirper.com/blog/collective-nouns-for-groups-of-various-birds/ for more) would be hierarchical in that those with the most kills/whatever would be seen as higher-up and therefore a more competitive nature would be uncovered, perhaps leading to some members sabotaging others.

Alternatively, if these creatures live isolated lives then they could perhaps be found dying all over the place, desperate - especially in winter months. This desperation could drive them to cruelty and dive-bombing even the largest groups of creatures that they would have no hope of overcoming because they are so close to death. Or they could be ruthless and complete in the annihilation of their prey and kill any other competition in their area.


Pennycuick, C. J. Modelling the Flying Bird. 2008.

https://sites.google.com/site/anthonysgurps/dragon-physics What is the maximum size of a flying creature?



If gravity was 1.5 times stronger, a flying creature would need 1.5 times the lift to fly. This could be achieved by flying faster or flying through denser air, but either flying faster or flying through denser air would increase drag. The net effect is 1.5 times gravity requires 1.5 times the power to fly.

Given the limits seen in large flying creatures on Earth I suggest that a 10m wingspan creature flying in 1.5 times gravity well is not possible using biology as we understand it on Earth.

One possible way to get around this would be to introduce some novel biochemistry that can generate much greater amounts of power than terrestrial muscles can. There might be evolutionary pressure towards this in a higher gravity field. The scope of chemistry is huge especially organic chemistry. There are an astronomical number of possibilities so I wouldn’t be surprised if something along these lines was possible.

The other option that would also probably evolve would be light weight muscles and bones. Finally if the creature is only required to glide down onto its prey and doesn’t have to take off from the ground life would be much easier. This might be achieved near cliff edges with strong thermals of a denser atmosphere. A creature could use powerful thermal currents to its advantage to gain height then double back over the top of the cliff and find some prey along the top of the cliff edge. If it could walk as well (likely as it has 6 legs) then it could stray further away from the cliff edge. But landings below the cliff would probably be fatal or at the very least involve a very long walk.


One thing that could explain large size is a decent Ozone Layer, I saw something about a guy who grew a giant piranha using nothing more than having additional Ozone in the micro-ecosystem he created for it...

  • $\begingroup$ Ozone layer is way up in the stratosphere. Very unlikely that the flying creatures would fly up to that height. And the atmosphere is thicker, ozone layer is unlikely to reach down to the atmosphere. $\endgroup$ Nov 18, 2019 at 14:33
  • $\begingroup$ I was in no way suggesting for it to fly to the ozone layer - The idea was instead to answer - If it is what could explain why it reached such a large size? in the original question, by suggesting more ozone so that the creature could grow to a larger size. $\endgroup$
    – ForgeAus
    Dec 5, 2019 at 10:49

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