All ant and termite species these days are social, and they owe much of their worldwide success to their ability to organize into hierarchies. But exactly when this advanced sociality (or eusociality) appeared remained unclear. Now, researchers studying 100-million-year-old amber recovered from Early Cretaceous Myanmar have discovered the oldest evidence of ant and termite societies. Their findings are published as two studies in Current Biology this week.
Eusocial animals are specialized into castes: Queens reproduce while workers and soldiers care for and defend the colony. Ants are the first major group of ground-dwelling predatory insects to become eusocial, and advanced sociality in termites is thought to have evolved during the Late Jurassic, some 150 million years ago. However, the earliest known soldier and worker termites date back to between 17 million and 20 million years, and because of poor preservation, Cretaceous-aged ants have been rare, until now.
Two teams led by researchers at the American Museum of Natural History (AMNH) and the University of Kansas (KU) have examined exceptionally well preserved ants and termites from Burmese amber dating back 99 million and 100 million years, respectively. These insects represent the earliest branches of their lineage, and while they looked very different from their modern relatives, the team found compelling morphological evidence for sociality in both Cretaceous insect groups.
After analyzing aggregations of worker ants in the amber, Phillip Barden and David Grimaldi of AMNH discovered signs of group recruitment as well as combat (pictured above) between the workers of different ant species, a social feature of ants today. "We know that wingless solitary relatives of ants don't fight or defend territories against other species," Barden said in a statement. "But modern ants war all of the time. The behavior of these fossil ants, frozen for 100 million years, resolves any ambiguity regarding sociality and diversity in the earliest ants."
Grimaldi, Michael Engel of KU, and colleagues found six termite species preserved in the amber, including both workers and soldiers. At least two of these species are new to science: Krishnatermes yoddha (pictured below) and Gigantotermes rex. The latter is named for the size of its soldiers, which is the largest known for termites. These findings also revealed that ants and termites (fierce enemies these days) lived close to each other during the Cretaceous as well.
A reproductive Krishnatermes yoddha termite. D. Grimaldi and P. Barden/AMNH