Heelripper

Located in The Burrows, Azj-Kahet. Spawns as part of the "Escape the Burrows!" phase of the "Kaheti Hospitality" zone campaign quest. These NPCs appear in the first wave and will be mowed down very quickly by Alleria and Anduin, so your best strategy is to stand well away from your companions and draw one of these spiders off as soon as it appears. You can abandon and restart the quest as many times as you like until you successfully tame the colours you want. This is a once-only campaign instance, though it's uncertain if party sync will allow you to repeat it.