They alarm each other with Isoamylactate and they seem to lay traces to their hive. There is also a pheromone, produced by the larva, which causes the adults to warm the cocoons. Other pheromones are not known yet. Both species are hunters. But Hornets also hunt wasps and restrict their population growth.
Hornets also hunt at night so they also catch night-active insects like moth.
All Wasps and Hornets don't return to the old nesting site. Despite this, Bumblebees show a return behaviour. Other Bumblebee-species have a worst memory and don't return. This service was launched 1991 by Berlin's administration. The service should inform the citizens about the biology of endangered Wasps and Bees.