Ariadne Spinners was a shop in Knockturn Alley that sold spiders. It carried a number of varieties, including nocturnal, venomous, bird-eating, and the "world's largest" (possibly the giant huntsman spider). A sign on the exterior of the shop stated that these spiders were "good for pets."
Ariadne was a figure in Greek mythology. She was the keeper of the labyrinth that contained the Minotaur, and assisted the hero Theseus in navigating the labyrinth by giving him a spool of thread so he could mark the path back to the entrance.