I'm not sure if these guys turn into War Wamoura, or they just come like that, but it's basicly a giant white moth. It was using the same abilities as these guys, not sure if they are new for level 6 Beseiged. (Cause I havent been to any Beseiged lower than 6 since the update) The War Wamoura seem weaker though than Wamoura (also couldnt get a screenie cause it died in less than a few minutes.. so I doubt its one of the new BNM)
These things use several different attacks which makes them nasty to be around during Besieged:
Amber Scutum: Defense Boost, like Cocoon. Heat Barrier: Blaze Spikes x5, deals nasty damage but can be dispelled. Thermal Pulse: AoE fire attack, deals pretty hefty damage. Vitriolic Spray: Breath attack with additional effect of Burn.
If you can help it, try not to stand too close to these things during Besieged, especially if you're a mage. The Burn effect inflicted by Vitriolic Spray is much worse than regular Burn, so make sure you have Erase on hand if you get hit. If you're a RDM or a BRD, try and Dispel the Heat Barrier, it'll save a lot of damage to a lot of people.