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Physiology
Like other insects, S. invicta breathes through a system of gas filled tubes called tracheae connected to the external environment through spiracles. The terminal tracheal branches (tracheoles) make direct contact with internal organs and tissue. The transport of oxygen(O2) to cells (and carbon dioxide (CO2) out of cells) occurs through diffusion of gasses between the tracheoles and the surrounding tissue and is assisted by discontinuous gas exchange (DGC ). As with other insects, the direct communication between the tracheal system and tissues eliminates the need for a circulating fluid network to transport O2 (Klowden, 2007). Thus, S. invicta and other arthropods can have a modest circulatory system even though they have highly expensive metabolic demands (Hill et al. 2012).

S. invicta faces many respiratory challenges due to varying physical properties of its environment including increased dessication, hypoxia, and hypercapnia. Hot, humid climates promote an increase in heart rate and respiration which potentially increases water loss (Klowden, 2007, Elzen, 1986). Hypoxia and hypercapnia can result from S. invicta colonies living in poorly ventilated thermoregulatory mounds and underground nests. DGC may allow ants to survive the hypercapnic and hypoxic conditions frequently found in S. invicta burrows. DGC is ideal for adapting with these conditions by being able to increase the period of O2 intake and CO2 expulsion independently through spiracle manipulation (Vogt and Appel, 2000).

Metabolic rate of tissues, which indirectly affects respiration, is also influenced by environmental temperature. Peak metabolism occurs at approximately 32°C (Porter and Tschinkel, 1993). Metabolism, and therefore respiration rate, increases consistently as temperature increases. DGC stops above 25°C, although the reason for this is currently unknown (Vogt and Appel, 1999).

Respiration rate also appears to be significantly influenced by cast. Male S. invicta show a considerably higher rate of respiration than females and workers. This is due, in part, to their capability for flight and higher muscle mass. In general, male S. invicta have more muscle and less fat resulting in a higher metabolic O2 demand (Vogt and Appel, 1999). While metabolic rate is highest at 32°C, colonies often thrive at slightly cooler temperatures (around 25°C). The high rate of metabolic activity associated with warmer temperatures is a limiting factor on colony growth because the need for food consumption is also increased. As a result, larger colonies tend to found in cooler conditions because the metabolic demands required to sustain a colony are also decreased (Porter and Tschinkel, 1993).