When do platypuses use their spurs?

Only the adult male platypuses have a spur. This venomous spur on each of their hind legs is the means by which they can deliver a venom strong enough to kill a small dog, and to cause almost paralysing agony to an adult human. Platypus venom also contains a protein which lowers blood pressure, also inducing shock.

It appears to be a defence mechanism, although there has been little opportunity for research to determine the spur's purpose.

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.