See you kill one wasp and the others get really up set about it.
I bet that the brush fire had the insects scurrying.
Anyway you really do not want to get stung by a wasp because unlike bees wasps can keep stinging and they also bend into a "U" shape so they can garb what ever they are stinging and also bite with the mandibles.Which I am sure makes the intake of the venom more likely and it also hurts.
I have been stung by a wasp a few times in my day they hurt even if you are not allergic.