This may be among the most weird first contact stories I've seen so far. With sufficiently different body chemistry & evolutionary environment, how hard can it get to recognize alien life & communicate with it, even if you notice there is (alien) intelligence somewhere around? This is actually a failed contact story, in spite of much effort from both sides.
Story summary.A sessile, long-lived, technologically far in advance of us, star faring race of aliens extensively mines metals off all sorts of worlds. A "Conservationist", a sort of policeman to prevent unauthorized mining, has noticed some "poachers" attempting to steal metals off earth. His approach makes them run away, but they've left behind "mole robots", bombs that will cause much upheaval in earth's crust to turn its metals-denuded surface into a metals-rich surface again in a few million years. Which means death for much of local life.
He'll land here, & notice obvious signs of intelligence. But all through his attempts to communicate with humans, he won't even realize they're the ones he's trying to help.
Fact sheet.First published: As a novel with additional material by Sam Merwin in Satellite Science Fiction, February 1957 as "Planet for Plunder". I'm not sure when the pure original novella version first saw the light of the day - probably 1972 in Robert Hoskins's anthology "Strange Tomorrows".
Related: Stories of Hal Clement.