See my Patch 4.2 Rare Pet Briefing Post for an updated guide on how to tame Solix, as well as the other 9 Patch 4.2 Taming Challenge pets.
Solix is a rare orange lava spider being added in the 4.2 Firelands Patch. He can be found in the Molten Front, within the Igneous Depths.
Solix is among the eight new Taming Challenge pets, so he requires a little more planning and effort than the drop a Freezing Trap and tame types of pets.