The duck-billed platypus, Ornithorhynchus anatinus, found only in eastern Australia, lives in streams, rivers, and occasionally lakes with year-round water. It feeds mostly on bottom-dwelling aquatic insect larvae, which it finds by probing the streambed with its pliable, sensitive bill. It grows to a maximum size of 1 to 2.4 kg (2.2 to 5.3 lb). One of only a few venomous mammals, the male platypus has a poison gland in the hind leg that opens through a bony spur on the ankle. The spur is used to defend against predators and possibly to defend its territory against other males. The females lack the venom gland and bony spur.
