Tie this one up with ants dying in the sugar, insects on your plate and lions eating your steak. Duolingo has taught me that in Italy I should prepare my own food.
Yeah, now I have to shake out my boots every time I want to wear them :) Io ho paura di serpenti :)
Why is this a question? Couldn't it also have meant:
The spider is under the cheese.
It would seem that in Italian, as in English or French, a question can be posed by simply making a statement and adding an inflexion at the end. In the case of the written language, the inflexion is represented by a '?'. So you're right, it could have been a statement, but the '?' made it a question.
I suppose you could say 'The spider? Is it under the cheese?' But Renato is correct when he says that your construction is not proper English.
Because it's not proper English. The word order that you write is just... wrong.
You don't need "it" in this case. If you say, "The spider is under the cheese?", it means you are surprised to hear that the spider is under the cheese. If you say, "Is the spider under the cheese?", it means that you don't know if it's under the cheese or not.