Dolichovespula spp. include the Dolichovespula media, Dolichovespula sylvestris and Dolichovespula saxonica. When viewed from the front, they appear to have a longer face than Vespula spp. (which have short, round faces). This is because the malar space (the gap between the bottom of the eye and the top of the mandible) is significantly longer in Dolichovespula spp. than it is in Vespula spp.
Please watch the videos linked below for more information on each species.