Why does a cockroach not die after its head is cut off?
Based on an article here, unlike humans, cockroaches have an open circulatory system. They don't have a huge network of blood vessels like that of humans, or tiny capillaries that you need a lot of pressure to flow blood through. Hence after you cut their heads off, very often their necks would seal off just by clotting.
According to the article cockroaches breathe through spiracles, or little holes in each body segment. Plus, the roach brain does not control this breathing and blood does not carry oxygen throughout the body. Rather, the spiracles pipe air directly to tissues through a set of tubes called tracheae. In addition cockroaches are poikilotherms, or cold-blooded, meaning they need much less food than humans do. Hence cockroaches can survive decapitation.
Although the answers to date are all factual and sufficient to answer the question why cockroaches would live without its head, some answers don't seem to be necessary as explanations.
Summarizing the given answers so far.
- Roaches' simple circulation would still function without its head.
- Roaches' decentralized respiratory system can still function without its head.
- Roaches are cold-blooded and demand less energy.
However, chickens can live without its head as long as the injury does not significantly damage its brain stem, which controls the animal's vital reflexes such as respirations.
- Chickens do have complex network of blood vessels and capillaries.
- Chickens don't breathe via spiracles and do have centralized respiration system like us.
- Chickens are warm-blooded.
Thus, an animal (such as a cockroach) can live headless if its remaining organs can still control its "vital functions".
Cockroaches are insects which means their brain is distributed.
The predominant characteristics of the cockroach central nervous system (CNS) are its segmented nature and decentralization of control processes (Ganihar et al., 1994; Pipa & Delcomyn, 1981)
. There is a pair of ganglion on each segment- head, thorax and abdomen. The ganglion on head is controlling the antennae inputs,proboscis,mandibles,eyes etc. When we cut off its head the ability to control all the above described organs fails(although, that doesn't matter because these organs are also decapitated) & it can't eat.. but the ganglion on the thorax is actually responsible for the breathing and digestion of food(with the help of ganglion on the abdomen). So if there is any food in the gut it will be normally digested and cockroach can live days consuming this energy. Also when head is gone there is no need to provide resources for the organs in head. So it can live more days by saving these resources.Plus, it can copulate if it is placed properly and this copulation is controlled by the ganglion on the abdomen.