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How Insects Breathe (noticing.co)
249 points by srikar on Nov 13, 2015 | hide | past | web | favorite | 35 comments

One reason insects breath differently than we do is that the surface to volume ratio between us is so different. Naturally, volume increases as the cube of the linear dimensions of the organism and the surface area only increases as the square of the dimension. This means that the ratio S/V is directly proportional to the size of the organism. A mouse has a much lower terminal velocity when falling than a human, for example, because they have a higher surface to weight ratio (weight of course is related to volume). Insects are so small that breathing doesn't require the mechanisms that we require because their S/V ratio is so so much larger. On the other hand, desiccation is a much greater problem for insects as is surface tension when wet. For these reasons, insects often have waxy coatings or other means of protecting themselves from drying out or being trapped in by a water drop, but an ant doesn't have to worry about falling out of a tree.

Surface/volume ratios are responsible for a lot of other things in nature, like the size/metabolism of mammals compared to the mean temperature of their habitat. (Eg, even within the same species, larger specimens are typically from colder climates)

EDIT: go figure, they have a related article: http://noticing.co/on-size-and-metabolism/

Yup, we also have another post that's specifically about the idea you describe: http://noticing.co/on-size-and-warmth/

Isn't the article saying the exact opposite? Insects' size (and thus S/V ratio) is in part limited by their breathing mechanism, not the other way round.

Hi, I'm one of the authors of the piece. Thanks for voting us up here. Hope you like what we're doing, and let us know what you think. If you're looking to read more of our posts, you can follow the blog on twitter @noticingblog (or on RSS). Cheers.

Your website is extremely well done.

1. Great typography. 2. Useful illustrations and 3. A great single column layout, which is easy on the eyes. 4. No annoying popups asking me to subscribe to mailing list. 5. Loads super fast.

And to top it all, the actual content is amazing. I am subscribed!

* your persistent banner is thoughtless

* AdBlock : noticing.co##HEADER.site-header

Can a decrease in oxygen from 35% down to 21% really explain a decrease in insect size from eight-and-a-half feet down to just 3 inches? Is there an interesting mathematical relationship here, or are there more factors at work?

Great question!

We spoke to Jon Harrison about this (the scientist we interviewed who studies insect growth & respiration). He says that the truth of the matter is we don't know the answer, it's still a hypothesis that the way insects breathe keep them small. There are other competing explanations, like that it's insect's exoskeletons that constrain their size, or ecological arguments (fewer predators means they can grow bigger). Also spiders don't use trachea to breathe but are also small.

One piece of evidence favoring the oxygen hypothesis is research that shows that the fossil record on giant insect size correlates with the oxygen levels in the past, all the way up until birds evolved (and wiped out the ecological niche for giant flying insects!)


And I'm told there's some more interesting work along these lines that's yet to be published.. so hopefully we should know more soon.

Lastly, there's all kinds of experimental work on breeding insects in high oxygen environments, but the results so far aren't universal.. some kinds of insects grow bigger, other's don't. The idea being that oxygen can help the insect grow but can also do damage to cells (in a way similar to aging), so you may need a long while to evolve and adapt to higher oxygen levels.

> Lastly, there's all kinds of experimental work on breeding insects in high oxygen environments, but the results so far aren't universal..

In my completely uneducated experience, it seems like this should be easy to test. Wouldn't it be easy/cheap to over-oxygenate a room, and put bug-farms in there. Is it more complex than that?

The issue, I think, is that experiments like that would only tell you so much, because the insects aren't adapted to the high levels of oxygen (which can be kinda toxic, particularly at higher concentrations). So to really understand this you'd need to breed insects in high oxygen over many, many generations, and have them evolve in this new environment. That takes a lot of time and money. Jon's lab has done it with fruit flies, and they do grow bigger over the generations. But as far as I know (which isn't a lot), folks haven't done those kinds of multi-generation experiments in many species.

Good to see this piece gaining some traction here. I'm a big fan of your work and Robert's too

I'm holding my breath for next week when you reveal which insect breaths through its butt!

Reads like a "Radio Lab" episode...

or "brave new world" the short lived ABC science show ...

The Robert Krulwich does your illustrations? Very cool.

If you enjoyed this, you will probably also like J.B.S Haldane's essay, "On Being the Right Size": http://irl.cs.ucla.edu/papers/right-size.html

So, are the conclusions based on science? Not speculation or correlation re: size of insects and oxygen density. 35% oxygen to 21% doesn't seem to account for a millipede going from 8 feet to 15in.

The oxygen level is only a single factor here, there are probably many more that influenced the size.

There's compelling evidence for a causal link. Hundreds of millions of years ago the atmosphere was much more oxygen-rich than it is today. Insects were also far bigger.

I enjoyed the piece. It felt like reading an episode of RadioLab.

I guess this explains why you don't need to buy expensive and dangerous wasp spray. A squirt bottle with a thick mixture of soap will kill them in seconds by cutting off their ability to breath.

I wish at least beginning science and math books had been written like this :)

Given that there are various ways to breath, I wonder if an artificial means might ever be substantially more efficient than natural lungs?

Nicely done. I would love to see such a schematic for fish too.

The circulatory systems of different creatures would be neat to see. Frogs have a weird, sponge-like heart, for example, and plenty of little critters have their entire bodies filled with "blood."

Oh my god that header is huge

I agree; it didn't work well on a half-small browser window. Either make it even smaller and the header goes away automatically, or open the JavaScript console and run


Interestingly, humans breathe in a second way not mentioned in the article. The eye's cornea actually receives its oxygen directly, through the process of diffusion. https://www.quora.com/Do-our-eyes-breathe

This is incredibly well done. Kudos to the author for the attention to detail and the informative read!

What would happen if you bred insects in a 50% oxygen environment?

What a great article!

all the smugness of RadioLab mixed with the talking-down-to-ness of VOX. Thanks, #content internet!

> [...] smugness [...] talking-down-to-ness

I read the entire thing and I didn't get the impression of either. In fact it even said they didn't know for sure how the passive system works but that this is one theory and then explain it.

Seemed like a good read overall and I didn't feel talked down to or anything.

Please don't do this here.

This is for children, right? All of this stuff is taught in school.

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