Some nests of German wasps certainly do grow to huge dimensions
in New Zealand (and in Tasmania and parts of the Australian
mainland), but the majority of nests are annual-ie they die with
the approach of winter or during the winter.  The largest
overwintering nest I have seen had a volume of about 3 cubic
metres.  It is nests of this size that can send out fleets of
foragers all winter long to attack honey bee hives within a
kilometre or so which can be of considerable economic detriment
to honey bee keepers.
The existence of nests which have survived at least one winter
suggests that nests could survive many winters, but unfortunately
whenever such nests are discovered, the discoverer (who is
frequently a beekeeper) destroys the nest, or has it destroyed.
As far as I am aware, no nest is known for certain to have
survived more than a first summer, the following winter, and a
second summer.
With the advent of the Common wasp, Vespula vulgaris, throughout
the country, and the displacement of the German wasp from much of
our beech forest, the opportunity to study the overwintering
phenomenon seems to be decreasing.  However, the Common wasp is
itself showing something of the same overwintering ability, so
perhaps not all is lost.
One beneficial aspect of this displacement as far as beekeepers
are concerned, is that Common wasps do not display the same hive
attacking propensity as German wasps .  On the other hand,
however, Common wasps are far more numerous in beech forsts that
produce honey dew than German wasps ever were, so greater volumes
of honey dew are being removed now.
We are hoping that our biological control effort will begin to
have some localised beneficial results in a few years.  Bee World
in a month or so will outline the problems caused by wasps in New
Zealand, and the progress of our biocontrol effort to date.