Police in north Adelaide are investigating a bizarre armed robbery from a home, involving the theft of 12, one-year-old snakes.

Police say that a woman living in the outer northern suburb of Hewitt opened the door to her home and a man with a black pistol threatened her.

The man made demands for "12 non-poisonous green-tree snakes" to be handed over to him; the snakes were kept in the house and each of them was worth $9000.

The man put the snakes in a duffel bag and tied up the woman and her two children.

Police, still on a hunt for the man, say that he is well built and has a deep voice; he appears to be in his 30s.

He had a black goatee and was wearing blue trousers and a shirt; he also had on sunglasses and a brown hat.