Ants: How Losing Armor Helped Them Conquer the World
The age-old economic dilemma of quality versus quantity extends far beyond human markets. A groundbreaking study by researchers from Britain, America, and Japan reveals how this trade-off profoundly shaped the evolutionary success of ants, one of Earth’s most dominant and adaptable insect groups. Their findings suggest that as ant societies grew in complexity and size, they didn’t simply shrink their workers – they strategically reduced investment in individual protection, paving the way for global conquest. This shift, seemingly counterintuitive, unlocked a remarkable capacity for diversification and resilience.
The Cost of Protection: Why Armor Became a Liability
In the insect world, the exoskeleton, or cuticle, is a vital component. It provides crucial protection against predators, pathogens, and dehydration, while also serving as an anchor point for muscles. However, building and maintaining a robust cuticle is a metabolically expensive undertaking. It demands significant resources, including nitrogen and rare minerals like zinc and manganese. For a solitary insect, a compromised exoskeleton can be a death sentence. But ants, through the power of collective living, found a way to circumvent this limitation.
“There’s a fundamental question in biology about how individuals change as the societies they inhabit become more complex,” explains Evan Economo, an entomologist at the University of Maryland and co-author of the study. “Individuals may become simpler because tasks that a solitary organism would need to handle can be distributed across a collective.”
The Hypothesis: Collective Benefit Over Individual Defense
Economo’s team hypothesized that in social insects like ants, the metabolic cost of cuticle investment could favor the colony as a whole over the individual worker. The logic is compelling: a colony of 10,000 workers can absorb the loss of a few individuals to predation without significant disruption. Investing heavily in the defenses of each worker, therefore, might represent a wasteful allocation of precious nutrients. The researchers aimed to determine if ant lineages with large, specialized workforces demonstrably reduced investment in their workers’ exoskeletons.
Scanning Superorganisms: The Power of Antscan
To test this hypothesis, the team embarked on a comparative anatomical study of ants at an unprecedented scale. “We collaborated with researchers worldwide, utilizing scans of ant specimens from diverse geographical locations to capture the global diversity of ants,” says Economo. The cornerstone of this research was Antscan, a massive database containing three-dimensional X-ray microtomography images of ants from across the globe.
Microtomography operates on principles similar to medical CT scans, but at a significantly higher resolution. However, generating the data was only the first step. Interpreting the vast amount of precise information required innovative solutions. “Parsing through 3D imagery of over 880 specimens – including workers, queens, and males representing over 500 different species – presented a significant challenge,” explains Arthur Matte, a researcher at the University of Cambridge and lead author of the study. “The 3D scanning technology is advanced, but manually segmenting every tissue of interest was incredibly time-consuming.”
Unsupervised Segmentation: A Computer Vision Breakthrough
To overcome this hurdle, Matte developed a novel computer vision algorithm for “unsupervised segmentation.” Because the cuticle is consistently the outermost tissue of an arthropod, the algorithm could automatically identify and measure the volume of the exoskeleton across all ants in the dataset. This automated process dramatically accelerated the analysis and ensured consistency.
The Numbers Tell the Story: Cuticle Investment Varies Widely
Initial results revealed a remarkable range in cuticle investment, varying from just 6 percent to 35 percent of an ant’s total body volume. The next crucial step was to understand the factors driving these variations. The team began investigating correlations between cuticle size and factors like diet, temperature, humidity, and foraging style.
To achieve this, the segmented 3D scans were integrated into sophisticated evolutionary models. “One of the most insightful aspects of our approach was individually removing variables from the models to estimate their contributions to the final cuticle investment,” Matte explains. This allowed the researchers to isolate the impact of each factor.
The Colony Size Factor: A Key Driver of Evolution
The analysis revealed that temperature accounted for only 12 percent of the variation in cuticle size, while diet – specifically its nitrogen content – explained another 37 percent. However, the most significant factor influencing cuticle investment was colony size. Ants that invested less in their cuticle consistently exhibited significantly larger colony sizes.
Even more surprisingly, this reduction in cuticle investment and the resulting increase in colony size were associated with higher diversification rates. In evolutionary terms, less armored ants were able to evolve and occupy new ecological niches much faster than their heavily protected counterparts. “Reducing nitrogen requirements could make these ants more versatile and capable of colonizing new environments,” Matte suggests. This efficiency may have facilitated a dietary shift from high-protein prey to more abundant, but less nutritious, liquid sugar sources like honeydew or floral nectar.
“Ants are reducing per-worker investment in one of the most nutritionally expensive tissues for the benefit of the collective,” Matte summarizes. “They’re shifting from self-investment toward a distributed workforce.”
The Power of the Collective: Echoes of Multicellularity
The researchers believe the pattern observed in ants reflects a broader trend in the evolution of societal complexity. The transition from solitary life to complex societies mirrors the evolution of multicellular organisms from single-celled ancestors.
A single-celled organism must be a “jack-of-all-trades,” performing all functions necessary for survival. In contrast, multicellular animals often exhibit simpler, more specialized cells that rely on the collective for protection and resource acquisition.
“This pattern echoes the evolution of multicellularity, where cooperative units can be individually simpler than a solitary cell, yet collectively capable of far greater complexity,” says Matte. However, whether underinvesting in individuals to benefit the collective applies to other species remains an open question. It’s likely not solely about nutritional economics, but also about reproduction.
Expendable Servants: The Role of Reproductive Division of Labor
The study focused on ants with a reproductive division of labor, where workers do not reproduce. This social structure is likely a crucial prerequisite for the “cheap worker” strategy. The team argues that this explains why similar evolutionary patterns haven’t been observed in more complex social organisms like wolves or humans, who maintain a strong individual interest in reproduction. Ant workers can be considered expendable because they don’t directly pass on their genes – they are essentially extensions of the queen’s reproductive strategy.
Future Research: Expanding the Scope of Analysis
Before searching for similar quality-versus-quantity trade-offs in other species, the team plans to delve deeper into the world of ants. Economo, Matte, and their colleagues aim to expand their analysis to other ant tissues, such as the nervous system and muscles, to determine if the cheapening of individuals extends beyond the exoskeleton. They are also investigating ant genomes to identify the genetic innovations that enabled this shift from quality to quantity. “We still have a lot to learn about ant evolution,” Matte concludes.
Source: Science Advances. 2025. DOI: 10.1126/sciadv.adx8068