Asked by: Amir Montazer, Iran
Decapitation is almost immediately fatal to humans because we have a high-pressure circulatory system that we depend on to keep our tissues oxygenated. Cutting the carotid arteries in your neck would cause you to bleed out completely in a few minutes. Even if the cuts were immediately cauterised, your body can’t survive without nerve signals from the brain telling you to breathe.
But cockroaches, like most insects, are different. They breathe passively through a network of pipes connected to holes called spiracles along the length of their body. They don’t rely on blood circulation to move oxygen around and their body fluids are at a much lower pressure anyway. Their brain mostly handles the sensory input from the eyes and antennae, with many other behaviours, like running and reacting to touch, handled by ‘mini brains’ called ganglia in each body segment. A decapitated cockroach will eventually starve to death but this can still take several weeks.