Ravenous Spider has a Forced effect: After Ravenous Spider engages you, it makes an immediate attack.

Can I use A Light in the Dark to return Ravenous Spider back to the staging area before it makes its immediate attack?

You don't have time to play A Light In The Dark before Ravenous Spider initiates its attack. During the attack at any action window you can return it to the staging are with A Light In The Dark, but returning an enemy to the staging area doesn't cancel the attack that's already been initiated.