Why evolution rewarded ants that sacrificed protection

The question is playful and unrealistic, but it points to a serious idea: the tension between quantity and quality. New research suggests this same tradeoff has shaped evolution, especially in the rise of complex animal societies.

How ants choose numbers over toughness

A study published on December 19, 2025, in the journal Science Advances reports that some ant species organize their colonies by prioritizing numbers rather than individual strength. These ants invest less in each worker’s cuticle — the hard outer layer of the exoskeleton — which frees up valuable nutrients. Those resources can then be used to produce more workers. According to the researchers, this approach of creating many less-protected ants instead of fewer heavily armored ones proved to be evolutionarily successful. The findings help explain how individuals can change as large, complex societies develop, including those seen in humans.

“There’s this question in biology of what happens to individuals as societies they are in get more complex. For example, the individuals may themselves become simpler because tasks that a solitary organism would need to complete can be handled by a collective,” said senior author Evan Economo, chair of the Department of Entomology at the University of Maryland.

In this context, individuals can become what scientists describe as “cheaper.” That means they require fewer resources to build and can be produced in larger numbers, even if each one is less physically robust.

“That idea hasn’t been explicitly tested with large-scale analyses of social insects until now,” said Economo, who also holds the James B. Gahan and Margaret H. Gahan Professorship at UMD.

Why ants are ideal for studying social evolution

Ants offer an unusually good system for exploring how complex societies evolve. Depending on the species, ant colonies can range from just a few dozen members to many millions.

“Ants are everywhere,” said lead author Arthur Matte, a Ph.D. student in zoology at the University of Cambridge. “Yet the fundamental biological strategies which enabled their massive colonies and extraordinary diversification remain unclear.”

The research team proposed that colony size might be linked to how much ants invest in their cuticle.

The cost of building body armor

The cuticle plays several important roles. It helps protect ants from predators, drying out, and disease, and it provides structural support for their muscles. At the same time, it is expensive to produce because it requires limited nutrients such as nitrogen and various minerals. Making a thicker cuticle uses more of these resources, which could restrict how many individuals a colony can support.

To investigate this idea, the researchers analyzed a large dataset of 3D X-ray scans from more than 500 ant species. They measured both total body volume and cuticle volume, finding that investment in the cuticle varied widely, from 6% to 35% of an ant’s body. When these measurements were fed into evolutionary models, a clear trend emerged: species that devoted less of their body to cuticle tended to form larger colonies.

Bigger colonies through collective strength

While thinner cuticles leave individual ants more vulnerable, the authors suggest this tradeoff may actually encourage the growth of large societies. Reduced armor may go hand in hand with other helpful social traits, including cooperative foraging, shared nest defense, and division of labor, all of which tend to become more pronounced as colonies grow.

“Ants reduce per-worker investment in one of the most nutritionally expensive tissues for the good of the collective,” Matte explained. “They’re shifting from self-investment toward a distributed workforce, resulting in more complex societies. It’s a pattern that echoes the evolution of multicellularity, where cooperative units can be individually simpler than a solitary cell, yet collectively capable of far greater complexity.”

The researchers also found that lower investment in the cuticle was linked to higher diversification rates. Biologists often use diversification, which reflects how frequently new species form, as a marker of evolutionary success. Economo noted that very few traits have been connected to diversification in ants, making this result especially striking.

Why less armor may lead to more species

Exactly why reduced cuticle investment promotes speciation is still unclear. One leading idea is that ants with lower nutritional demands can expand into environments where resources are limited.

“Requiring less nitrogen could make them more versatile and able to conquer new environments,” said Matte, who began the work during his master’s program while interning in Economo’s lab at the Okinawa Institute of Science and Technology in Japan.

The authors also suggest that as ant societies became more complex, group-level defenses such as collective nest protection and disease control reduced the need for heavy individual armor. This may have created a reinforcing cycle. Lower cuticle investment allows colonies to grow larger, and larger colonies further reduce the pressure for each ant to be strongly protected.

“I think of this as the evolution of squishability,” laughed Economo. “Many kids have discovered that insects aren’t all equally robust.”

Other social organisms, including termites, may have followed similar evolutionary paths, although that possibility still needs further testing.

What ant societies can teach us about humans

The findings also have implications beyond insects. The researchers draw parallels to human military history, where heavily armored knights were eventually replaced by specialized soldiers such as archers and crossbowmen. Economo also pointed to Lanchester’s Laws — mathematical equations developed during World War I that examine when large numbers of weaker fighters can overpower a smaller force of stronger ones.

“The tradeoff between quantity and quality is all around. It’s in the food you eat, the books you read, the offspring you want to raise,” Matte said. “It was fascinating to retrace how ants handled it through their long evolution. We could see lineages taking different directions, being shaped by different constraints and environments, and ultimately giving rise to the extraordinary diversity we observe today.”

The paper, “The evolution of cheaper workers facilitated larger societies and accelerated diversification in ants,” was published in the journal Science Advances on December 19, 2025.

This research was supported by the Okinawa Institute of Science and Technology, the Japan Society for the Promotion of Science KAKENHI (24K01785), the University of Cambridge and the General Research Fund 2022/2023 (17121922) from the Research Grant Council of Hong Kong. This article does not necessarily reflect the views of these organizations.