I think he's a human astronaut. His boots have germs he is not aware of, which prove fatal to the aliens. It might be by Arthur C. Clarke.

marked as duplicate by user14111 story-identification May 14 '17 at 0:21

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  • There is a lot of guidance in this post to help you describe the story you're looking for in more detail - you can edit in anything else you remember. – Gallifreyan May 13 '17 at 21:41
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    Vaguely reminiscent of Clarke's "Before Eden", which was the answer to this other question. Could that be the one you're thinking of? – user14111 May 13 '17 at 22:36
  • That's it! I just read it. It's a wonderful cautionary tale. I thank you for pointing it out to me. – Robert Garner May 14 '17 at 0:07