why do bugs like mosquitoes not die when we hit them while they’re flying?

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why do bugs like mosquitoes not die when we hit them while they’re flying?

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Acceleration.
As they say, it’s not the fall that kills you, it’s hitting the ground.

Take a parkour artist for instance. A parkour artist can fall from great heights without suffering serious damage, even when most normal people would be injured by the drop. This is because they know how to land properly, which is to say, absorb the impact slowly.

If you hit asphalt with straight legs, all the energy is absorbed at once. This, however, is not what you want, as now, your bones are subjected to a big burst of energy coming in all at once. If, in contrast, you bend your knees and allow them to act like a spring as you land, the time you take to come to a full stop is longer. It might still hurt, but the odds of injury are much lower this way.

With the insect it’s a similar thing. If you hit an insect mid flight, it’s subjected to the same energy it would be subject to when hit against a solid surface. However, if you hit it in mid air, the insect gets flung around, but it’s a flying insect, they can stand a bit of airflow around them, and since their tiny bodies only allow for a very rudimentary brain, they’re not always smart enough to avoid a collision, so instead they evolved to be able to take the occasional impact. Therefore, unless you hit the insect at really high speeds, it can take the blow, because it just tumbles around a bit until it can regain control.

Hitting it against a hard surface, however, that’s a different thing. The insects body has no way to absorb the energy it experiences slowly, since it has no room left to do so. It has to take the force all at once. And doing that is enough to kill it, even if the blow wouldn’t be anywhere near fatal in mid air.

[Edit: trying to simplify and use smaller words as requested…]

There is a physics principle that has a huge influence on “what is the right size” for a successful creature shape, and it’s basically the ratio of surface area to volume, often called the square-cube law because of the relationship between x^2 : x^3.

In other words, as things get bigger volume gets big *way faster* than surface area gets big. Here’s why that matters:

One of the best known descriptions for this concept goes like this:

>Toss a mouse from a building. It will land, shake itself off and scamper away. But if similarly dropped, “… a rat is killed, a man is broken, a horse splashes.”

[summarizing source](https://www.edge.org/response-detail/27082)

[Original source, pdf](https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.phys.ufl.edu/courses/phy3221/spring10/HaldaneRightSize.pdf&ved=2ahUKEwj2w-Lm_KD7AhXiFTQIHSIaBuoQFnoECCMQAQ&usg=AOvVaw0zcy8CJNvk6sVDBn86rkOR)

That goes to your question about the tiny bug hitting a windshield.

**Why is this the case?**

Some physics principles and some biological processes are directly affected by the volume of a certain mass, like structural strength, or heat retention, gravity,

While other processes are directly affected by the surface area available, like photosynthesis, heat transfer/radiation, diffusion of chemicals or gases (e.g. lungs), surface tension of water, etc.

So all biological systems are making constant trade offs between these two options. Bigger isn’t always better. And neither is smaller.

**Examples:**

Exoskeletons depend on surface area, but muscle strength depends more on volume, so there’s a limit on how big a successful insect can be.

An elephant needs proportionally big thick legs and leg bones to hold up it’s mass, but goats or dogs are fine with skinnier legs.

Trees maximize surface area with leaves to take in more sunlight without weighing too much for the tree to support.

Artic creatures tend to be big with a compact geometry to maximize heat retention while minimizing the surface area that can leak heat.

Lungs have to fit inside the volume of the chest cavity, but on the inside the fractal lung sac paths have a mind boggling amount of surface area to facilitate oxygen absorption by the bloodstream.

(I want to add more, but I gotta get to work… dang trade offs)

[Edit: took this out and moved to the end since it was interrupting the flow…]

When x is small, like say 2, then area-to- volume, or x^2 : x^3 is 4 : 8, or not that far apart, and x^2 is still a large proportion, 50%, of x^3.

If x gets big, like 100, then x^2 : x^3 is 10,000 : 1,000,000, so proportionally x^2 is only 0.1% of x^3. That 50% vs 0.1% has big implications.

If its a small enough insect then the air from your hand swinging at them gives them a speed boost so the relative speed when your hand actually makes contact with them isn’t always enough to kill them. Heck half the time the crazy wind currents are enough that you don’t even end up making contact with them.

In addition without a solid surface to squeeze them against, they can transform that energy you transfer to them into acceleration. If a car driving in front of you is going 60 mph and you hit it at 70mph it’s not going to do that much damage, especially if the driver in front doesn’t hit the brakes to stop it. Instead you’re just giving it a really aggressive push.

It might do some damage but insects have a hard exoskeleton so they can take a bit of a rough push without causing too much damage.