Defenders: Hold of Felyal
The Second was well aware of the unfortunate fate of their predecessors and as their march brought them closer to the edge of the Felyal, they halted travel early enough to assemble a pre-fabricted fort for every night. In addition, a full third of the army were on duty while the rest slept.
To provoke his opponents, General Tynan ordered troops to burn some of the outskirts of the forest during the day once they had reached it. The Loquae of Felyal, for their part, assembled every Mantis of fighting age, along with their totem cousins, then fell on the army in the dead of night.
While the ready troops struggled to assemble a firm defense, the inapt warriors rampaged through the fort. It looked like a repeat of the previous battle was in the offing when the Engineers managed to fire their engines. Immediately bright lanterns lit up the camp as bright as day and the tempo of the entire battle had been changed. No longer hampered by the darkness, Snapbowmen were able to co-ordinate and scyth down the attackers.
The battle itself continued for a while even after the conclusion was obvious: Mantis honour could not let them flee from presumably inferior opponents.
Result: Despite taking more casualties than the opponent that they had sprung a trap on, the Wasps had completely broken the spirit of the Mantids. The Wasps then advanced through the forest, razing and burning as they went, killing the last few holdouts at extortionate cost. Then again, there's always more Wasps