Ten to fifteen minutes following death, a large release of CO2 is produced in many species when killed by high temperature. Studied in mosquitoes, hissing cockroaches, grasshoppers, and desert harvester ants, this post-mortal peak (PMP) appears to be temperature-dependent and, to our knowledge, does not occur in insects killed by means other than high temperature. Four effects were applied to common house crickets (Acheta domestica) to analyze the origin and properties of the PMP. First, it was shown that the PMP does not occur without oxygen. Second, post-mortal CO2 release was studied as a function of temperature-exposure following death and it was established that the phenomenon is dependent on extreme temperatures and runs to completion when exposed to temperatures above 60°C. Third, basic and buffered solutions were employed to assess the possible involvement of dissolved HCO3- (bicarbonate), the dissolved form of CO2, in production of the peak. Hemolymph factors like bicarbonate did not appear to have an effect on the PMP. Finally, exposure to hydrogen cyanide inhibited the PMP, demonstrating the involvement of mitochondria and cytochrome c oxidase in particular. Together, these results rule out any effect of hemolymph or possible CO2 stores in the body of an insect on the PMP. The PMP occurs as an aerobic mitochondrial reaction that requires high initiation temperatures. We believe that this underlying cause may be mitochondrial breakdown at high-temperatures. More specifically, fluidity of the mitochondrial membranes likely increases with high heat, disabling the established proton gradient and ATP production. The resultant accumulation of electron carriers allows for cyclic, but futile operation of the citric acid cycle and electron transport chain with remaining pyruvate stores.