Outpost on Io is a short science fiction story by Leigh Brackett.

Pendleton's quiet voice was grave. "Mars is old and tired and torn with famine. Venus is young, but her courage is undisciplined. Her barbarians aren't suited to mechanized warfare. And Earth..." He sighed. "Perhaps if we hadn't fought so much among ourselves..."

”MacVickers studied the Europan with the hating eyes of a wolf in a trap. His smooth black body had a dull sheen of red under the Jupiter-light. There was no back nor front to him, no face. Only the four long rubbery legs, the roundish body, and the tentacles in a waving crown above.

MacVickers bared white, uneven teeth. His big bony fists clenched. He took one step toward the Europan.A tentacle flicked out, daintily, and touched the silver collar at the Earthman's throat. Raw electric current, generated in the Europan's body, struck into him, a shuddering, blinding agony surging down his spine.”

Outpost on Io was first published in Planet Stories magazine in 1942. 6,000 words, average reading time 30 min. 

Leigh Douglass Brackett (1915-1978) was an American author, particularly of science fiction, and has been referred to as the Queen of Space Opera. She was also a screenwriter, known for her work on such films as The Big Sleep (1946), Rio Bravo (1959) and The Long Goodbye (1973). She was the first woman shortlisted for the Hugo Award.