There is this short story about a (scientist?/explorer?) who goes to either Mars or Venus or a certain exoplanet (accompanied by his wife) which is in a tidal lock such that the dark side is very cold for a human being, and harbors vicious creatures. I think one of the two was a botanist. The sun side is too hot for a human, so they conduct their short time on the planet at the borderline of day and night, which is not a very broad strip. Anyone got a clue about this story?
Could this be "The Lotus Eaters" by Stanley G. Weinbaum?
A month after the events in "Parasite Planet", Hamilton "Ham" Hammond and Patricia Burlingame are married, and thanks to Burlingame's connections, the two have been commissioned by the Royal Society and the Smithsonian Institution to explore the night side of Venus. There they find a species of warm-blooded mobile plants with a communal intelligence that Burlingame nicknames Oscar. Oscar is very intelligent, quickly picking up English from Hammond and Burlingame.
The humans learn that the Oscar beings reproduce by releasing clear bubbles full of gaseous spores. When the bubbles burst, the spores come to rest on another Oscar being, eventually grow into another individual, and bud off. In "Parasite Planet", the vicious, night-dwelling Triops noctivivans used these bubbles to attack Hammond and Burlingame, since the spores have a soporific effect on humans.
The humans are horrified to learn that, being plants, the Oscar beings have no survival instinct. Despite their greater-than-human intelligence, the Oscar beings react with indifference when the local trioptes attack and consume them. This prompts Burlingame to name their species Lotophagi veneris – the lotus eaters of Venus. Hammond and Burlingame barely escape the trioptes themselves after exposure to the spores leaves them almost catatonic.
It is in "Parasite Planet" that they establish the vicious creatures.
After a time, Hammond suffers an attack of conscience, turns, and follows Burlingame south. He catches up with her in the foothills of the Eternities just before a huge doughpot traps them in a box canyon. Hammond is able to get off two shots of his flame pistol at the doughpot before the barrel shatters, reducing the thing's size but still leaving them trapped. They decide to go deeper into the box canyon, but in the darkness they are set upon by Triops noctivivans, vicious nightside-dwelling cousins of the Venusians. The trioptes drive them back toward the doughpot, dosing Burlingame with a soporific drug that renders her unconscious. Hammond is forced to make his way past the doughpot on a low, narrow shelf of rock while carrying Burlingame.
"Lotus Eaters" can be read in Astounding Stories, April 1935, available at the Internet Archive.
I found my references in Is there any sci-fi story about intelligent extra-terrestrial life on a tidal locked planet?, which I found via a search for science fiction short story explorer and wife on tidal-locked planet.