They explode on contact wih their target for about 22k fire dmg. As its fire, shamans fire elemental can take care of them without harm :). If you have some time before pull, pop-up fire elemental and watch.
Engineers CAN deconstruct these. A paladin in my raid just got 3x [Handful of Cobalt Bolts] from one.
The smart tactic for these is to have someone jump in an Arachnopod Destroyer, they can then "pounce" into the middle of the pack with the Boomer XP-500 mobs. All of the Boomer XP-500 mobs will explode, after which the raid tanks can run in and pickup aggro.