In the hornets case I don't believe they suffocate it, but the ball of bees temp. at core kills the hornet as honeybees can take a much higher temp.
That's what I learned anyways
From the article:To kill a hornet, Asian honeybees will mob it and generate so much heat that the hornet dies. But Cyprian honeybees fight with a type of hornet that is adapted to hot climates and can withstand such "thermo-balling." According to researchers in France and Greece, the Cyprian bees swarm the hornet's abdomen and block the breathing holes, called spiracles. Cause of the hornet's death? Suffocation. The scientists named the attack "asphyxia-balling."
And today you learned something new.