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Ok, so I have an unfinished/W.I.P world (may turn it into story) about a sapient civilization of cockroaches called Roachins that are pretty much German Cockroachs, but most/many can fly and can stand on 2 legs and use their 1st and 2nd set of legs like we use our arms.

Anyway, they have pretty much the same tech as modern humans have, vehicles like cars, helicopters, and ships. Also tools like ladders and the like.

Now, irl, most roaches are good or decent runners and fliers, and can swim to an acceptable level. I handwaved it by saying that at least a certain country of Roachins got too 'domesticated'(human-like), and now they cannot run as fast, fly as well, or swim as well. This has also effected their climbing abilities.

Basically, I got to thinking about how some insects and spiders take damage from falling like tarantulas and big beetles, while most/many do not because of their size or build, and thought that having this group of Roachins take fall damage because they kind of got a bit fatter for their size, and maybe their exoskeleton a bit weaker, would be an interesting touch.

So, could a Roachin from this country feasibly take fall damage without having to fall like from something like a human scale skyscraper? Maybe more so a Roachin scale skyscraper, so like 6-7 (maybe 8) feet fall. Would it kill or at least hurt them badly?

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    – L.Dutch ♦
    Mar 29 at 1:54

3 Answers 3

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Small creatures do not get damaged from falling because they quickly reach terminal velocity and thus do not hit that hard on the ground.

The only way to get away from this and get falling damage is to either make the falling thing more chubby, therefore having more mass will also have higher terminal velocity (which would be in line with being domesticated and therefore less lean), or to make so that the landing happens on an unfortunate configuration; think of landing joint first or not using any protective reflex (like a man stumbling and not using their hands to protect their head).

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    $\begingroup$ Or reduce air pressure so terminal velocity is higher... $\endgroup$
    – Penguino
    Mar 26 at 21:18
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    $\begingroup$ doesn't help from that height unless gravity is a lot higher as well. after falling 2m you just have a speed of 6m/s even in a vacuum. $\endgroup$
    – ths
    Mar 26 at 22:29
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    $\begingroup$ @ths 6 m/s could cause injury to a weak, unprepared human so it could cause injury to a weak, unprepared cockroach. There's a misconception that smaller animals can handle falls better because of the square-cube law. Nope; the scaling factors actually cancel out. Bigger animal is weaker but also has longer legs to absorb the impact gradually. It's only air resistance that helps smaller animals handle higher falls. The converse of falling is jumping, and tigers jump higher than house cats. (in meters, not relative to body length). web.mit.edu/6.055/old/S2009/notes/jump-heights.pdf $\endgroup$
    – causative
    Mar 27 at 5:30
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    $\begingroup$ Even humans can easily survive a 2m fall mostly if not entirely unharmed, unless they land on their head or something. A creature the size of an insect won't be even remotely harmed by such a fall, even without air resistance slowing their fall. $\endgroup$
    – Darrel Hoffman
    Mar 27 at 15:26
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    $\begingroup$ @causative the role of the square-cube law isn't a misconception here. It's directly relevant to why air resistance helps smaller creatures more than larger creatures. $\endgroup$
    – Carl Kevinson
    Mar 27 at 20:06
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Not feasible

Even if you scale them up to the size of a mouse, terminal velocity is only about 15 m/s, which is generally survivable by all but the most fragile creatures, especially since the squared-cubed rule makes smaller creatures proportionally stronger. Rule of thumb provided here is that:

Terminal velocity for animals is approximately 90 d0.5 m/s, where d is the diameter of the animal in meters.

The only way to make a creature that size take damage from any conceivable falling distance is to have it fall on a very delicate body structure while unconscious (as per the answer by L.Dutch), or to fall onto a dangerous chemical or electrified surface. With even vestigial flying ability, an out-of-condition, office-working cockroach will still be able to land on its feet without taking damage.

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    $\begingroup$ "Especially since the square-cube law makes smaller creatures proportionally stronger" - not for falls. The smaller creature is proportionally stronger but also their body is able to deform proportionally less before taking damage. As a result the velocity at which you are injured upon hitting a hard surface is fairly independent of your size. It's only air resistance that protects the cockroach. See web.mit.edu/6.055/old/S2009/notes/jump-heights.pdf for jump height, which scales the same way as fall height. $\endgroup$
    – causative
    Mar 27 at 5:21
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    $\begingroup$ @causative I disagree. Just look at what would happen to an upscaled human. He would crush his own bones with his weight just by standing (due to the square-cube law). Falling even small distances would be devestating for the giant. Smaller creatures are much sturdier in comparsion to their body size. $\endgroup$
    – datacube
    Mar 27 at 7:47
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    $\begingroup$ @causative I cannot see how these jumps translate into dangers of accidental falls. A cat can fall from high and land relatively safely given that it will land on its feet but a tiger will just smash because its limbs cannot take the impact. $\endgroup$
    – Jani Miettinen
    Mar 27 at 12:30
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    $\begingroup$ @JaniMiettinen That's because of air resistance, and in fact despite urban legend domestic cats can be severely injured from multi story falls. pets.webmd.com/cats/guide/cat-high-rise-syndrome $\endgroup$
    – causative
    Mar 27 at 13:31
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    $\begingroup$ @causative that is only true for proper nad complete damageless landing (landing feet first and absorbing all the fall energy into muscle movement). Edit: The remaining energy is then is transferred into deformation energy, which will then range from a "bit pain" to "breaking bones or exosceleton" depending on the amount of Energy left and the sturdyness of the bodyparts. $\endgroup$
    – datacube
    Mar 27 at 14:06
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Yeah, pretty much the same as everyone else has said ─ insects and other surface-heavy animals barely take damage from falling at all. cockroachzone.com notes that "Cockroaches don't get injured, let alone die, from falling [...] irrespective of the height they fall from."

If the cockroaches were larger, or had a lower surface area, they could conceivably take some falling damage, but not significantly. Also, it may be relevant that adult cockroaches can glide/fly for short distances.

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