Metabolic Scaling of Social Insects

There is a clear order to how animals use energy. Specifically, there is a clear relationship between the metabolic rate of organisms and their masses. Known as Kleiber's Law, this has been known for nearly a hundred years. Specifically, metabolic rates scale sublinearly with the mass of different animals, which means that as species get bigger, they use less energy per pound:

More recently, this has been explored in cities, and it has been found that infrastructure and energy usage can scale sublinearly (larger cities have fewer gas stations per capita, for example), but productivity and innovation often scale superlinearly -- we get increasing returns for patents and ideas in cities.

So the natural question is then, What about insect colonies? Insect colonies are in that weird liminal space between individual organisms and cities. Several years ago, a team of researchers set out to answer this question. As the researchers argue:

The theory and empirical work on this subject have shown that there are economies of scale related to energy use such that cells in larger, more complex animals require less energy per capita. For eusocial colonies, it has long been posited that these "superorganisms" experience similar relationships with colony size, perhaps owing to shared constraints on the delivery of energy and materials (e.g., branching distribution networks, space-filling surface area to volume constraints). But empirical evidence for these relationships is scarce. This hypothesis deserves further attention because, if unitary organisms and eusocial colonies show the same size-dependent allometries with respect to energy use, this may suggest that selection acts on colonies much as it acts on individuals.

So they tested this, finding somewhat mixed results. Metabolic rate (based on oxygen consumption) seems to scale according to a 3/4 power with mass and hence is sublinear, but it turns out that it is indistinguishable statistically from scaling linearly. However, since the results are fairly consistent across species, it is likely that there is sublinear metabolic scaling in social insect colonies.

And this is bolstered by the fact that colonies grow just like individual organisms. As seen below, just as animals start small and grow larger according to a certain shape, so do insect colonies:

This is certainly gratifying for anyone who has read Gödel, Escher, Bach and remembered its sentient ant colonies. Now just be careful with that magnifying glass.

Top image: Samantha Henneke/Flickr/CC