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What is the body density (in $\text{g}/\text{cm}^3$) of insects and is there a list of animals and their value of body density?

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A recent studya measured the volumes (using a 3D scanner) and masses of 113 different insect species. They found the following relationship between the mass of the insects and their volumes ($V[mm^3]$ and $m[mg]$):

$\ln (V) = 1.019 \ln (m) + 1.46$

$\Leftrightarrow V = 4.30596 m^{1.019}$

Thus, since $\rho = \frac m V$

$\rho(m) = \frac m {4.30596 m^{1.019}} = \frac {0.232236} {m^{0.019}} $

Figure: Scatter plot of the measured masses and volumes

enter image description here

Reference:

a Kühsel, S., Brückner, A., Schmelzle, S., Heethoff, M. and Blüthgen, N. (2016), Surface area–volume ratios in insects. Insect Science. doi:10.1111/1744-7917.12362

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    $\begingroup$ @AndreasJørgensen If you find an answer helpful, upvote using the arrow up button. Additionally, you can mark an answer as accepted by clicking on the checkmark icon. The function gives density in $\frac {mg}{mm^3}$, so just multiply with $10^3$ to get $\frac g {mm^3}$. $\endgroup$
    – adjan
    May 13, 2017 at 0:27
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    $\begingroup$ *Divide by $10^3$. $\endgroup$
    – canadianer
    May 13, 2017 at 0:50
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    $\begingroup$ @daniel from mistakenly assuming my calculator's $\log$ was $\log_{10}$, not $\ln$. $\endgroup$
    – adjan
    May 13, 2017 at 18:23
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    $\begingroup$ @AlexDeLarge If you had read the edit comment you'd have known that this is a current SE bug and it makes no sense to change all HTML sup's on SE because it just got broken today. I used it in many of my previous answers and the bug only occured today. Wait till the SE team has fixed it! $\endgroup$
    – adjan
    May 18, 2017 at 14:46
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    $\begingroup$ @DominikS I think now it should be correct $\endgroup$
    – adjan
    Jun 28, 2017 at 19:16
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I did the following estimate, based on the honey bee, to get an idea of the order of magnitude of the density of insects: According to Wikipedia (sorry for the german), we have:

  • The average mass of a honeybee is about 80 mg.
  • The length is 12 mm in average.

In order to estimate the volume, I model the body in three parts (see Wikipedia again):

  • The head as a sphere with a diameter of roughly 2.5 mm
  • The torso as a sphere with a diameter of roughy 4 mm
  • The abdomen as a cylinder of length 6 mm, and a diameter of 4 mm.

This will yield a very rough estimate of the volume, but we can expect it to have the correct order of magnitude. It is:

$$ V \approx \pi \cdot\Big (\frac 43\cdot \Big(\frac {2.5}2\Big)^3 +\frac 43\cdot \Big(\frac {4}2\Big)^3 +\Big(\frac 42\Big)^2\cdot 6\Big)\approx 117\text{ mm}^3 $$.

We have not accounted for antennae, legs, ..., so given the uncertainties of my estimates, the volume of a honeybee should be in the range of 100-200 mm^3. This is also in accordance with the graph in @adjan's answer.

With this the density of a honeybee should be between 80/200 and 80/100 mg/mm^3, so $$0.4\,\frac{\text{mg}}{\text{mm}^3} < \rho <0.8\,\frac{\text{mg}}{\text{mm}^3}$$,

which is interestingly slightly less than the density of water.

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