As far as I understand questions and statements are identical in Italian, with the only difference being the tone it's said with / the presence of a question mark.
Unlike in English when we have to reshuffle some of the words around to make a question a statement and vice versa.
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.