Life Without A Head.

If you're not impressed enough with the fact that cockroaches could out-survive humans in a nuclear incident, why not try this one for size....

Cockroaches can survive up to one month without their head!!

"Headstrong" (I thank you, I'm here all week!!)

We, as humans, cannot imagine this is possible because we could not survive without ours.  Decapitating humans would not only deprive us of all the mechanisms of breathing and eating, but would also result in gratuitous blood loss and a drastic drop in blood pressure that would prevent transportation of oxygen and nutrients around the body, ultimately leading to death.

So how do cockroaches survive?

Well, for most of the reasons that humans need their head; cockroaches do not.  To breathe, cockroaches inhale and exhale through tiny valves, called spiracles, of which there are two pairs in the thorax and eight pairs in the abdomen.  The spiracles are openings to tubular structures that split into an internal network called tracheae, similar to capillaries, which deliver oxygen directly to vital tissues.  Where humans rely on the brain to maintain the close relationship between the respiratory and autonomic nervous system that controls our breathing, the mechanism in cockroaches relies on carbon dioxide (CO₂) levels.  As levels of CO₂ increase, the valves open to release the gas in exchange for oxygen.  In fact, decapitation also removes the respiratory inhibitory effects of the subesophageal ganglion, found in the head, and the rate of breathing actually increases and maintains a constant rate. 

The nervous system of the cockroach is also quite amazing.  It is organised into a number of ganglions, distributed like a spinal cord, through the whole body.  The amazing fact about these is that even without the brain, the remaining ganglion continue to function independently and allow the cockroach to perform simple responses such as standing, moving and reacting to touch (after pondering over this fact, it did make me wonder what else a cockroach could actually do, it's not like it can dance or rollerskate is it?).

Decapitating a cockroach does not result in fatal blood loss because, unlike humans, they have a low-pressure open circulatory system that, when ruptured, simply clots without exigency.  What I consider another amazing (but, at the same time, disturbing) fact about cockroach decapitation is that it is not just the body that can survive, even the head manages to remain "alive" (for want of a more suited definition) for some hours, showing signs of alert sensory responses, particularly in the antennae.

Lastly, to seal the lid on the box of these unbelievable decapitated cockroach facts, when the cockroach eventually dies from this marvel, if not as a result of infection or being preyed upon, it actually dies from thirst or starvation.  Cockroaches do not need to feed as regularly as humans and so the less time that has elapsed between eating a substantial meal and decapitation, the longer the little critters can survive.


References/Links

Choi,C.Q. (2007) Can a cockroach live without its head? Scientific American. 297 (5), 118.

http://www-bcf.usc.edu/~meshkati/tefall99/part2.html

http://webs.lander.edu/rsfox/invertebrates/periplaneta.html