Molting is a stressful event in insect development. When an insect molts, the individual discards its exoskeleton and sheds and renews the interior lining of substantial portions of the respiratory (tracheal) system. We profiled for the first time the disruptive pattern of respiration during the molting process in larvae of the mayfly Cloeon dipterum (Ephemeroptera:Baetidae). Molting induces a precipitous drop in O₂ consumption immediately followed by a surge in O₂ consumption that appears to be compensatory in nature. Postmolt metabolic suppression is consistently observed during which O₂ consumption rates lag relative to those of nonmolting larvae. Furthermore, the magnitude of respiratory disturbance during the molt increases as a function of temperature. Increasing temperatures increase molting frequency and the apparently stressful nature of the molt itself. Thus, the insect molt appears to be a previously unappreciated route by which warming conditions may affect aquatic insects.