MadSci Network: General Biology

Re: If all human population & all insect population were made into 2 blocks,

Date: Wed Jun 30 11:27:42 2010
Posted By: Steve Mack, Associate Staff Scientist
Area of science: General Biology
ID: 1277759916.Gb

If all human population & all insect population were made into 2 blocks, which would be bigger and by how much? I think the insects would be far greater but I don't know by how much.

Thanks for your question Terry.

I think that instead of answering your question in terms of the volume (the size of a block) taken up by all humans or all insects, I will answer your question in terms of the mass (the quantity of matter) represented by all humans and all insects. If you think about it, the answer to the question about the volume of all humans or all insects will depend on how you pack them together. Insects have stiff exoskeletons and lots of projections that will make it difficult to pack them together as neatly as you can with soft-bodied humans. In addition, there is really no limit to how densely you can pack matter, which is why black holes (stellar masses compressed to a single point) can exist. So, lets consider how much mass is involved, instead of how much volume.

The Smithsonian Institution provides a useful starting point for the answer to your question with this page about the total number of insects. At the end of that page, you'll notice a reference to a New York Times article indicating that there are 300 pounds of insects for every pound of humans. However, no reference to the New York Times article is provided.

I think that that Smithsonian page is referring to this 1991 article by New York Times science journalist Natalie Angier, in which she says that there are 300 pounds of insects and spiders for every pound of humans. However, this piece is really about the use of insects and spiders in films; it's not a scientific article.

More recently, in January 2009, Natalie Angier published this New York Times article, in which she uses a number of 200 pounds of insects per pound of human (no spiders this time). (The difference is likely due to a whole lot of spiders, as well as to the addition of 1.5 billion humans between 1991 and 2009).

Hölldobler and Wilson (2009) estimate that the mass of all ants* is roughly equivalent to the mass of all humans*, and that ants make up only 10% of all insect species. So, by that estimate alone, we can see that that the mass of all insects will be much greater than the mass of all humans. They also cite Williams' (1964) estimate that there are on the order of 1018 (1 billion billion, or 1 quintillion) insects alive on the Earth at any given time, and the Smithsonian article suggests 10 quintillion. Angier seems to use the 1 quintillion number in her 2009 article ( 6.8 billion humans * 1.5 billion insects/human = 1.02 quintillion insects) as well.

So, if those 1-10 quintillion insects weigh 200 times more than we 6.8 billion humans (assuming that the average human weighs between 50 and 70 kg), then the average weight of all insects is between 0.7 and 10 milligrams.

As estimates go, that doesn't seem too bad, so I'm inclined to go with the 200 to 1 mass ratio of insects over humans.

N Angier. A Large-Size Focus on Life Lived Small. New York Times. January 6, 2009. Page D1.
N Angier. What's Creepy, Crawly and Big in Movies? Bugs. New York Times. February 19, 1991.
CB Williams. Patterns in the balance of nature and related problems in quantitative ecology. Academic Press, 1964. New York.
Bert Hölldobler, Edward O. Wilson. The superorganism: the beauty, elegance, and strangeness of insect societies. W. W. Norton & Company, 2009. Page 5.

* caveat: Hölldobler and Wilson use the dry weights (biomasses) of ants and humans in their calculations. Comparisons of fully hydrated humans and ants may vary. Its not clear to me if Natalie Angier's ratio is derived from biomass or the mass of whole organisms.

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