I am here to clarify things.
I went out and investigated today. There is absolutely no proof that the species, Prenolepis imparis flew- no dead males, and the colonies I marked out did not look like they have had a mating flight any time recently (small nest entrances, not expanded for the exiting alates). I DID FIND QUEENS!!! I came home with five queens. Alza's first guess was correct. I collected four Dorymyrmex insanus queens, and one of what I believe is Dorymyrmex cf. bicolor. This would explain Alza's description of red head and thorax and black gaster, as my samples are identical to your descriptions. And yes, as Alza said, it obviously was a flight.
Queen- bright red with black gaster.( thought it was dorymyrmex SP at first )
Worker-Dark red with a black gaster ( knew it was myrmecocystus )
...
And yes, it was a flight.
