A E van Vogt's "M 33 in Andromeda" (short story, space opera, free): Smart humans vs galactic-scale monster
According to Wikipedia, title of this story is wrong: "M33 is in constellation Triangulum; M31, the Andromeda Galaxy, is in Andromeda."
Also, according to Wikipedia, it's one of the stories in author's fix-up novel, "Voyage of the Space Beagle".
Note this is a juvenile story; don't be too critical or logical. But it did appeal to heart - in a fun, mindless way.
Story summary.Anabis, a galactic scale alien creature in the form of mist that surrounds worlds & interstellar void of its galaxy, feeds on the "life force" of animals - it's satiated when an animal dies! It doesn't directly do any killings though - it just ensures conditions where there will be killings. That is why it has turned every habitable world in its galaxy to a jungle world - because such worlds have "prolific life-&-death cycles"!
Now human exploration battleship, Space Beagle, is approaching its home galaxy, & Anabis sees a new food source - in the galaxy where the ship came from. Only there are too many galaxies in the general direction the ship is approaching from.
So we see a war of nerves between humans in the ship & Anabis - reveal location of human home galaxy, please. Because it's a van Vogt story, humans will, of course, not only win but see to it that Anabis is destroyed.
Fact sheet.First published: Astounding, August 1943.
Download full text as part of the scans of Astounding issue where it originally appeared.
Among the stories from John Campbell's Astounding/Analog.
Part of the author's "Space Beagle" series.
Related: Stories of A E van Vogt.