What happens to wasps when it starts to get cold?

Most of them die off - especially the 'solitary' species.. I've already seen a number of dead and dying bees and wasps this year. They will have mated, and produced eggs which will lie dormant over the winter, to develop once the warm weather returns. The wasps that live in colonies usually 'ride out' the winter in nests either underground, or in disused buildings.