When Red Imported Fire Ants' nests are submerged by floods, they cluster together to form rafts that float on the water’s surface. This unique biological phenomenon was previously believed to be caused by surface tension. However, research led by Professor Hong Tsai-Ming from the Department of Physics at National Tsing Hua University (NTHU) challenges this theory. The study suggests that the ants' ability to form rafts is an active self-repair mechanism, likely facilitated by pheromonal communication that enables them to cling to one another and create a raft-like structure. This groundbreaking finding has attracted attention in the scientific community and has been featured in international media outlets such as CNN, Le Monde (France), and others across the U.S., Germany, and the U.K.

NTHU explains that typical materials tend to narrow and elongate when stretched, similar to dough when kneaded. However, Professor Hong's soft matter research team discovered that when a raft of red fire ants is stretched, the ants adjust by mobilizing those at the top to fill in the spaces at the bottom. This allows the raft to maintain its structure without becoming narrower or thinner. This characteristic, which is difficult to achieve with artificial materials, could potentially inspire the development of new biomimetic elastic materials. Such materials might enable the creation of miniature robots, as seen in science fiction, that can freely combine and switch between liquid and solid forms.

Professor Hong first learned about the surface tension theory in a lecture by a biologist who suggested that red fire ants form rafts due to surface tension. To investigate further, his research team, with assistance from the local government, captured ants from areas where farmers reported fire ant damage for their experiments.

The team discovered that other species of ants do not form rafts on water. Additionally, dead fire ants do not form rafts either, and the fire ants were able to form rafts even on dry, vibrating platforms, disproving the idea that the raft formation was due to surface tension.

The researchers found that when the fire ant nest is flooded, the ants use their mandibles and legs to grasp each other, creating a multi-layered web-like structure that allows them to float on the water. Upon closer examination of the raft structure, the team observed that the worker ants on the raft gradually moved from the center toward the edges, taking turns moving into the water and swimming to the bottom of the raft, much like a conveyor belt on a treadmill. Meanwhile, the queen and eggs, larvae, and other "passengers" remained on the raft, drifting and looking for a place to land.

Furthermore, if the raft’s surface is damaged, worker ants automatically move to repair it. This led Professor Hong to suggest that if the mechanism behind the fire ants' raft-building behavior could be understood, it might lead to the development of biomimetic materials that behave like both solid and liquid states, capable of self-repair and collective migration. This could be useful for applications such as artificial ligaments that require flexible, stretch-resistant materials.

While the exact mechanism by which fire ants communicate to form rafts remains a mystery, Professor Hong speculates that the ants may have evolved the ability to secrete special pheromones when in danger, signaling and coordinating the formation of the raft. However, more research is needed to fully uncover the details of this biological communication process.