Ant colonies vary in size from dozens to millions. The intuition is that larger colonies succeed through better protection — more soldiers, thicker armor, stronger defenses. Size should correlate with investment per worker.
Matte and colleagues used synchrotron X-ray tomography on 880 specimens from 507 ant species and measured exoskeleton thickness relative to body size. The finding inverts the intuition: species with thinner cuticles — less protective armor per worker — evolved larger colonies. And those lineages diversified faster, producing more species over evolutionary time.
The mechanism is resource allocation. Cuticle is among the most nutritionally expensive tissues an insect produces. A colony that reduces cuticle thickness per worker frees protein and chitin to produce more workers from the same resource base. Each individual is more vulnerable. The colony is more resilient — not despite the fragility of its members but because of it.
This is a general problem in scaling systems. The assumption is that robustness at the component level produces robustness at the system level. But component robustness has a cost, and that cost competes with the resource pool that determines system size. When the system can absorb individual failures — when redundancy substitutes for durability — the optimal strategy is to build cheaper, more replaceable units. The colony doesn't need each worker to survive. It needs enough workers to absorb losses. Thinning the armor is how you get enough workers.
The macroevolutionary signal is the sharpest finding. Lineages that adopted the cheaper-worker strategy didn't just grow larger. They speciated faster. The strategy unlocked not just bigger colonies but more kinds of colonies — as if reducing per-unit investment opened a design space that per-unit robustness had foreclosed.