I have maybe a thousand nymphs, but the adults comeinto a swarm of a few hundred or more, then within a few to several months they have all died off but a few, and then a few months later the cycle starts over. I have not really paid too much attention to it, but I get the impression they go several months as nymphs and then as much or less as adults, with the whole life cycle being a year and a half, maybe somewhat more. Definately far from the lifespan of say a hisser of some type (2 years maybe 3).
Personally if I had to repeat any of this thread anywhere else I would go with Orins post.