Normally, i don't like that pokémon gets an evolution so late, like Tangela from 1.gen evolves to Tangrowth in 4.gen, for example, but when the distance is only one generation, i can accept it, for example Golbat (1.gen) to Crobat (2.gen), in addition, in a situation like this where the pokémon only can evolve to a form in a certain region, i like this idea. Maybe the new spider-pokémon is a split evo. to Spinarak.