Lolth disagrees though :x

How This Shit WorksEdit

The transformation between drow and drider takes 12 hours and is extremely painful, and that's all we know from D&D "canon." Everything else was made up by Bob and Lumi with help from Chuck Wood, expert on weird anatomy problems.

The transformation can be broken apart into three four hour long stages.

Stage OneEdit

In this stage, there is little to no external obvious changes. The bones of the lower body begin to shift and change, which feels like a dull ache, but will become sharper as time progresses. The bones begin to grow and change shape, and the pelvis begins reshaping itself near the end of this stage.

Stage TwoEdit

The bones of the leg continue to split apart and grow, becoming hollow and thin, with more muscle growing inside of what will become the exoskeleton. Externally this looks like a horrible stretching and distortion of the legs and lower body. Though the legs appear bipedal, the victim will be unable to hold themselves upright, let alone walk, near the end of this stage.

Stage ThreeEdit

The new legs are still inside the old muscle and flesh. As they become the proper size and alignment, the new spider legs will literally burst out of the old legs, destroying the victim's lower body. Once the spider legs are free, they will rapidly grow to their full size, shifting into place on the reformed pelvis. The abdomen is also formed in this stage.

So the whole thing is horrifically bloody and disgusting and leaves shredded bits of skin and leg muscle all over, hooray.