Like other insects, the red imported fire ant 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 to cells (and carbon dioxide out of cells) occurs through diffusion of gases between the tracheoles and the surrounding tissue and is assisted by a discontinuous gas exchange. As with other insects, the direct communication between the tracheal system and tissues eliminates the need for a circulating fluid network to transport O2. Thus, red imported fire ants and other arthropods can have a modest circulatory system though they have highly expensive metabolic demands.