The square-cubed law is a big problem, and makes this creature impossible. But another problem exists and that is the fact that this is a hybrid.
Not only is this creature a hybrid, but it is a hybrid of two creatures drastically removed from each other on the evolutionary tree.
Take a look at this.
The further you have to go back to find a common ancestor the more difficult it becomes to have a plausible hybrid...and in the case of the dryder you have to go way way way back.
Arachnids are invertebrates and their systems are completely foreign to what makes up a human. Finding a plausible way for the two systems to work together is simply not possible. Thus the answer is magic on this one.
- Creating a centaur: Difficult
- Creating a bird person: Very Difficult
- Creating a kangaroo person: Super Very Difficult
- Creating a platypus person: Awesome
- Creating a Spider Person: Super Duper Very Difficult (also known as impossible)