Mechanisms of army ant bivouac thermoregulation

Tropical species have evolved to thrive amidst challenges such as high intra- and inter-specific competition, due to the abundance and diversity of species in the tropics. However, because of the relatively stable temperature ranges in the tropics, these species operate closer to their Critical Thermal Maximum (CT_max) compared to animals in other latitudes. This adaptation to a less variable temperature range can increase their risk of being negatively impacted by extreme temperature changes. Among tropical insects, Army ants are renowned predators that build self-assembled nests called bivouacs, by linking their bodies in a coordinated manner, providing shelter for themselves and their brood. Eciton burchellii army ants nest above ground, working as a superorganism to manage factors like nest site selection and internal bivouac temperature control to ensure colony survival. While it is clear that bivouacs can thermoregulate according to the brood's needs, the exact mechanisms remain unclear. We conducted a non-manipulative study across elevations to test several leading hypotheses for thermoregulatory mechanisms used by E. burchellii parvispinum army ants in the bivouac. We collected temperature measurements and analyzed image data to compare changes in nest structure in Monteverde and Santa Rosa (Guanacaste), Costa Rica, two zones with different altitudinal and ambient conditions. Here, we present intriguing findings that widen our knowledge of this species. Understanding the thermoregulatory strategies of these ants is crucial for developing predictive models that can assist in formulating more effective conservation strategies, especially in light of extreme temperature changes caused by climate change.