Translation:The spiders crawl down from the wall and crawl under the carpet.
You're right; the English sentence is more natural without it. I've come to think that the course designers were trying to make it easier to deduce the correct Hungarian sentence from the English one, and so they include a lot of little directional words like the "in" here which would ordinarily be omitted in English - but they give you a clue about what's expected in the Hungarian (you should use bemásznak). I just saw this reach an extreme in the "Alllative Postpotional Pronouns" (https://www.duolingo.com/skill/hu/Allative-Postpositional-Pronouns ) section where the English sentences are almost entirely Pidgin English designed to gloss the Hungarian.
Of course, this causes difficulty in the other direction, since you have to guess an unnatural English sentence if you're given the Hungarian one. And there are some inconsistencies about when and how this philosophy is applied, so it's a bit frustrating.
Perhaps with time the course developers will be able to standardize their choices better, and use the Tips & Notes section to let us know what to expect. It's not unreasonable to use slightly "bent" English for educational purposes if it helps to understand all the parts of the Hungarian sentences. But it's the sort of thing you should be clear and consistent about, and draw attention to, at the outset.
Spiders sometimes crawl, or do a movement that could be described as crawling. But climb is definitely better here.
In general, it seems like 90% of the time Duolingo should accept either crawl or climb for mászik. It usually only accepts crawl, though. That's usually the less good alternative.