Early ants may have had complex social lives, fossil data suggests

Even the earliest ants may have been social butterflies.

Ants fossilized in 100-million-year-old amber have sensory equipment that suggests they had complex social lives similar to their modern-day ancestors, researchers report June 14 in Science Advances.

All ants live in advanced societies where adults live in large groups and engage in cooperative parenting and divisions of labor, but ants’ ancestors were solitary wasps. Researchers aren’t sure when the insects’ social lifestyle evolved. Some early ants have been found fossilized as groups, which hinted at social living around the time of the insects’ evolution during the Early Cretaceous Period. But it was still unknown if early ants chemically communicated with each other as colony members or simply shared their habitats.

Ryo Taniguchi, a paleontologist at Hokkaido University in Sapporo, Japan, and colleagues examined three fossilized ants of one of the oldest known ant species, Gerontoformica gracilis. The fossils, preserved in amber, were unearthed in northern Myanmar and are now owned by the American Museum of Natural History in New York City. The team focused on the ants’ antennae, which have key tools for communication between nestmates (SN: 4/4/16).

The researchers developed a specialized microscopy technique for imaging multiple sides of the fossil antennae to better examine the ants’ sensilla — tiny projections that detect environmental cues. They compared the fossil ants’ suite of sensilla to those of six modern ant species.

G. gracilis had two types of sensilla that are known only in ants. These organs are used for identifying nestmates and detecting their alarm pheromones, which notify other ants of threats to the colony. Together, these unique sensilla help ants live together and defend the colony as a single unit.

Today, many ant species create massive colonies thousands to millions strong, but the researchers argue that the fossil record suggests that the earliest ants lived in very small colonies of a few dozen nestmates. Despite this, “we can consider that ants lived in a highly advanced social system even in their early evolutionary stages,” Taniguchi says. 

The new findings suggest that tens of millions of years before they became an ecological force in ecosystems around the world, ants may have been marching together.