The first one is the more common by far, and what people will assume you mean when there's no context.
For the second meaning it would be customary to say "Hva er det som spiser en krabbe?" to avoid any confusion. With context, it would of course be understandable even without rephrasing.
Why wouldn't it be something like "Hva gjør en krabbe spiser"? Maybe I'm using "gjør" incorrectly as an auxiliary verb, but the seqence of the "Hva spiser en krabbe" reads in the correct English-speaking order for "What eats a crab." And if the sentence is correct either way with no context, should it be considered incorrect? In translation engines, I'm finding the two English sentences translating as "Hva spiser en krabbe," with "Hva gjør en krabbe spise" showing up in reverse translation last week.
"Gjør" does not function as an auxiliary verb in Norwegian, neither in questions nor as part of any verb tense. There is also only one present tense in Norwegian, as opposed to the simple and continuous versions in English.
Translation engines are not to be trusted, and doubly so when dealing with smaller languages such as Norwegian (they receive fewer native corrections). However, they're safer to use when translating another language into your native language, as you'll at least be able to spot the gibberish yourself.
Thank you for your reply. I finally stumbled on how to access the threads of help for each answer that are available in the mobile edition. I'm deeply impressed by the time you and colleagues take in answering these questions. From what I think I've gathered, it really can be translated into English both ways... So I suppose one's imagining of the sentence depends on which nature shows one has watched, as to whether they are lunching or become lunch. Tusen takke! I'm also grateful that Norwegian doesn't require auxiliary verbs, as I understand it so far. Smart. :) Great language.
Bare hyggelig! :)
And yes, the Norwegian sentence allows for the crab to be either the subject or the object; the eater or the eaten, as it were. However, unless context indicates otherwise, one would assume the former. If you wish to express the latter, it's often preferred to phrase it unambiguously as "Hva er det som spiser en krabbe" ("What is it that [eats/is eating] a crab").
There are some auxiliary verbs in Norwegian, which you'll learn about later, but with your knowledge of English and German they should feel quite familiar.