🐜 More numerous or more robust? The choice of ants

In animals, nature frequently oscillates between producing a multitude of less hardy individuals and creating a limited number of very robust specimens. This trade-off between number and robustness manifests in many areas, from military strategies to biological systems.

Research published in the journal Science Advances precisely examines this dilemma within ant colonies. Scientists have observed that some species reduce investment in the cuticle, the protective layer of the exoskeleton, in order to generate a larger number of workers. This tactic allows for the development of large colonies, which can number millions of members.


Primarily, the cuticle protects ants from predators, dehydration, and pathogens. It also constitutes structural support for the muscles. However, its fabrication requires limited resources, such as nitrogen and certain minerals. A thicker cuticle consumes more of these nutrients, which could restrict the number of individuals a colony is capable of sustaining.

To test this hypothesis, the team measured the volume of the cuticle and the entire body of over 500 ant species using 3D scans. The observations indicated that cuticular investment oscillates between 6% and 35% of body volume. By cross-referencing this data with evolutionary models, a clear trend emerged: species that allocate fewer resources to their cuticle generally have more numerous colonies.

While a thinner cuticle makes each ant more vulnerable, it could nevertheless favor colony expansion. According to the authors, this reduction of individual armor is associated with advantageous social behaviors, such as collective food foraging and task division. Evan Economo, co-author of the study, draws a parallel with the emergence of multicellularity, where cooperative units, simpler in isolation, allow for the emergence of an elaborate collective organization.

This approach is also correlated with accelerated diversification rates, implying that species with less developed cuticles seem to differentiate more rapidly. The researchers suggest that a reduced need for nitrogen might help ants establish themselves in new environments. Furthermore, within vast colonies, group protection diminishes the necessity for each worker to possess powerful bodily defenses.

Analogies can be drawn with other systems, including human ones. In military history, for example, heavily protected knights gave way to more numerous and specialized units. Arthur Matte, lead author, notes that this balancing act between quantity and robustness is omnipresent, and that ants provide a compelling illustration of it from an evolutionary standpoint.