Fire ants, known for their painful stings, are highly adaptable insects that have developed a remarkable method for surviving floods. When their underground nests are inundated with water, these ants come together to form living rafts. This collective behavior allows the entire colony to float on the surface of the water, protecting themselves from drowning.
Formation and Structure of Fire Ant Rafts
A fire ant raft appears as a dense, interwoven mass of ants floating on the water’s surface, often resembling a reddish-brown mat. When floodwaters fill their underground passageways, the ants evacuate and begin to link their bodies together. They achieve this by grabbing onto each other’s legs, mandibles, and other body parts, creating a flexible yet strong mesh. This cooperative action results in a multi-layered, web-like structure that can be surprisingly large, sometimes exceeding 100,000 individuals.
The formation process involves ants moving from the center to the periphery of the emerging raft, taking turns descending into the water to form the stationary bottom layer. The queen, along with the colony’s eggs and larvae, are typically positioned safely within the drier, central layers of the raft, shielded by the adult workers. This tightly knit “weave” prevents water from penetrating the raft, ensuring the colony remains largely dry and buoyant.
The Science Behind Raft Stability
The ants’ exoskeletons are waxy and hydrophobic, meaning they repel water. This property allows them to trap air bubbles within the intricate network of their linked bodies, which increases the raft’s buoyancy. These trapped air pockets create a shimmering layer around the submerged ants, providing a breathable environment.
Surface tension also plays a role, as the collective weight of the ants is supported by the water’s surface. When ants are placed on water, they create slight depressions, and the slope of these depressions draws nearby ants together, a phenomenon sometimes likened to the “Cheerios effect”. The ants’ interlocking bodies create a material that behaves like a viscoelastic substance, allowing the raft to deform and absorb impacts without breaking apart. This material property enables the raft to stretch and flow, much like a non-Newtonian fluid, adapting to the surrounding water conditions.
Survival and Dispersal Through Rafts
The formation of rafts is a survival mechanism for fire ant colonies during periods of heavy rain and flooding. This behavior protects the queen and the vulnerable brood (eggs, larvae, and pupae) from drowning. The raft acts as a temporary, mobile home, allowing the entire colony to remain cohesive and viable until drier conditions return.
These living rafts also serve as an effective means of dispersal, enabling fire ants to colonize new areas far from their original location. Carried by floodwaters, these rafts can travel considerable distances, sometimes hundreds of kilometers, facilitating the ants’ spread into new territories. The resilience of the colony within the raft, which can remain afloat for weeks, contributes to the continuation of the species even in adverse environmental conditions.
Ecological and Human Implications
The ability of fire ants to form and disperse via rafts contributes to their status as an invasive species. Originating from South America, these ants have spread globally, establishing populations on all continents except Antarctica. Their rapid dispersal through floodwaters allows them to colonize new habitats efficiently, often outcompeting native species.
The ecological consequences of fire ant invasions include disruption of local ecosystems and a reduction in native biodiversity, as they aggressively compete with and prey upon native arthropods and other animals. For humans, the implications are substantial. Fire ant rafts can float into populated areas, leading to increased encounters with large numbers of aggressive, stinging ants. These stings are painful and can cause localized reactions, with a small percentage of individuals experiencing severe allergic reactions, including life-threatening anaphylaxis. The economic damage caused by fire ants, including agricultural losses and medical treatments, amounts to billions of dollars annually.