A human falling down from three times their own height (six metres or so) would be horribly injured, while bugs seem to just walk on. How does this work? Shouldn’t they be falling at a similar speed, due to gravity?
First, they don’t fall at a similar speed, they fall much much slower. Their “terminal velocity” is much slower. This is because they are very very very light, and they have a lot of surface area – lots of legs and appendages that cause drag. Because they are so light and cause so much drag. Air resistance alone is enough to slow down their fall to a survivable speed. It’s pretty much impossible for an ant to die from falling.
Second, their exoskeleton. Ants all basically have their own Spartan-Super-Suit like Master Chief that keeps them solidly in place, no organs splattering around because the organs are kept nicely in place by their strong exoskeleton.
Your assumption about falling at the same speed applies if there’s no air resistance, but there’s a lot of air resistance, and even a little bit of updraft will keep tiny bug airborne or at least greatly slow. It’s descent. On top of that, it’s not just about the speed with which an object falls. You have to consider the amount of mass involved in the collision between the ground and whatever’s hitting it. Ultimately, it comes down to the physics formula F = ma, which means force equals mass times acceleration. Assuming there was no air resistance, then the acceleration part of that formula is the same for both a person and a small insect, but the mass is greatly different. A small insect may weigh a fraction of a gram, while a human weighs 70 to 100 kg or more. Literally thousands of times more. That means there’s literally thousands of times the force acting on a suddenly decelerating human then there would be on a small insect. When you add in the effects of air resistance, the difference is even greater.
It’s like dropping a polystyrene box from hundreds of meters. doesn’t weight much to make a significant impact to cause injury/damage.
It’s because of terminal velocity, that is the point where acceleration from gravity balances out with resistance from wind. The average terminal velocity for an insect is about 2m/s, the terminal velocity for a human is about 60m/s. If both you and an insect jumped from the Empire State Building at the same time you’d reach earth a lot faster than the insect would, but if the experiment happened in a vacuum you’d be able to lock eyes with the insect and would both hit the ground at the same time and at the same speed… a blistering 86m/s or 192mph
Additionally things are just relatively stronger the smaller they are. Ants can lift 50 times their body weight, with minimal training an average child can dead hang for 2 minutes something adults struggle with, elephants can’t jump.
This is yet another consequence of the infamous “square-cube law”. The volume of a shape increases faster than the surface area of a shape as it gets bigger. So, insects have proportionally much more surface area than insides compared to a much larger animal. So they experience proportionally more air resistance than a larger animal. This means they can fall from heights and not fall fast enough to hurt themselves.