Why is a male platypus poisonous?

No. Adultmale platypuseshave venomous spurs on their ankles, which is different to being poisonous. Poison is ingested; venom is injected or administered by another similar method. Apart from several species of shrews and the Cuban solenodon, platypuses are the only venomous mammals.

Male platypuses have a venomous spur on each of their hind legs, through which they can deliver a venom strong enough to kill a small dog, and to cause almost paralysing agony to an adult human. It is possible that a very small child could be killed (though a tiny child would be unlikely to engage in behaviour threatening to a platypus), and it is also possible that the shock of the pain in an unhealthy, weakened adult could well result in their death. Also, platypus venom contains a protein which lowers blood pressure, also inducing shock.

People who have been "spurred" by a platypus report that the pain is strong enough to cause vomiting that may last for days, weeks or sometimes even months. The pain cannot be relieved by morphine and other standard pain-killing drugs. It seems the only way it can be relieved is through anaesthesia of the main nerve from the spur site.

Female platypuses do not have venom, but they are born with spurs. These spurs fall off by the time the young female is about a year old.