Starving Ants Guard Brain Energy First, Study Finds

When pavement ants starve, their brains keep running at close to full power while the rest of the body cuts back sharply, researchers at Boston University report. The result, published in the Proceedings of the National Academy of Sciences, shows a pattern of brain energy use that closely matches the pattern seen in humans and other mammals.

The human brain accounts for roughly 2% of body weight yet consumes about 20% of the body's energy. Pavement ant brains show a similar imbalance: they make up around 5% of body weight while taking roughly a quarter of total energy, according to the study. That mismatch has long been treated as a hallmark of large, social brains. The new work suggests it shows up in miniature brains too.

Lead author Zachary Coto, a member of Boston University's Traniello Lab, and colleagues measured brain metabolism and whole-body metabolism in worker ants. When the insects were deprived of food, whole-body metabolic rates fell markedly. Brain metabolic rates did not drop significantly, and the brain's share of total energy nearly doubled during starvation.

The team also tested whether starved workers could still do the social jobs a colony depends on. Within days of dying, starved ants still performed tasks such as nestmate identification and colony defence at levels comparable with ants that had been fed. The researchers read that as evidence that the brain keeps working at the expense of other demanding systems when food runs out.

A brain that refuses to power down

Researchers have proposed a "selfish brain" theory to explain the human pattern: when energy becomes scarce, the brain claims priority over other organs to preserve critical functions. Testing that idea directly in mammals has proved difficult, because measuring brain metabolism and whole-body metabolism together in the same animal is hard. Ants offered a way around the problem, since both measurements can be taken in the same small insects.

Coto described miniature brains as "expensive to run," a cost that persists even in social insects that put the colony above the individual. The finding cuts against an assumption that a tiny brain should be cheap to operate. Ant brains are far smaller and simpler than human brains, yet the study found they demand no less energy, relative to body size, than the brains of mammals.

To check the result, the team scaled human and mammalian data down to predict the energy use of a mammal the size of an ant. The model matched the ant species closely, which the authors took as a sign that shrinking a brain does not change its basic energy requirements. Size changes the absolute cost, but not the proportion the brain claims.

Why a tiny brain still costs so much

The result matters for how scientists think about brain evolution. Humans and ants both live in complex societies, and both rely on brains to navigate social relationships, recognise group members, and defend shared territory. That the same energy pattern appears in both lineages points to a deeply conserved feature of evolution rather than a quirk of large brains.

Ants and humans also share significant neurophysiological properties despite the gap in brain size and complexity, the researchers note, which makes ants a useful model for studying how social life shapes brain evolution. Tool use, social learning, personality, and numerical ability have all been documented in other species, including insects, and the new study adds energy budgeting to the list of traits that cross the species divide.

There are limits to what the work shows. The experiments used pavement ants under laboratory conditions, and the findings describe a single species rather than insects in general. The scaling model is a prediction tested against one ant species, not a direct measurement across many species. Even so, the core result held across the study's metabolic and behavioural tests: under starvation, the brain kept its share while the body gave ground.

The paper, titled "Energy prioritization and neurometabolic scaling in a social insect brain," appeared in the Proceedings of the National Academy of Sciences. Reporting on the study is available from Phys.org, and the paper itself can be found via its DOI record. More research stories appear in GenZ NewZ's science section.