why do bugs like mosquitoes not die when we hit them while they’re flying?
In: 3
[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.
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