Most people know from experience that cockroaches are difficult to kill. The common over-the-counter aerosol insecticides that are advertised as being specially formulated to kill indoor roach pests may be effective, but it often takes copious amounts of spray before roaches succumb to the poisonous effects of these products. Many people have likely noticed that these products are not killing roach pests as quickly and as effectively as they once did, and this is because cockroach pests are becoming resistant to the fatal effects of both professional-grade and over-the-counter roach insecticides. This unfortunate reality has been confirmed by numerous research studies, one of which saw scientists systematically amputate the limbs of cockroach specimens only to find that the limbs would sometimes grow back. As it happens, this phenomenon was brought to light over a century ago in a little known experiment carried out by a long forgotten biologist.

During the late 19th century biologist H.H. Brindley found that cockroaches have five joints on each of their six legs. However, some of Brindley’s roach specimens only had one or two legs with four joints each as opposed to the normal five. Brindley was initially perplexed by this discovery, but later on he observed that amputated legs would sometimes regrow, and when they did, the regrown legs had four joints only. Researchers are not exactly sure why this is, but they do know that cockroaches possess two leg joints that are far weaker than the other three. These two weak leg joints are equivalent to the hip and ankle joints in humans, and they likely evolved so that cockroaches could easily pull off their own legs in order to free themselves when their legs become trapped. Surprisingly, cockroaches can still move about, mate and eat with one or two missing legs, and it usually takes three to five months before an amputated leg fully regrows. Researchers are currently studying the molecular processes that fuel limb regrowth in cockroaches in order to mimic the process in humans who have lost limbs.

Have you ever encountered a cockroach that you noticed had been missing legs?