OK ive phoned my pest control help line.
Wasps and Hornets do not leave a pheremone or other marker for any location they place a nest into.
Nests are located purely on the basis of food (like a nice plum tree) so if the area has ample food they may return or may find another suitable place to build there nest.
CLuster however flies do leave scent markers so large colonies can build up over years as they scent mark locations to cluster over the winter months but they dont sting :socool:
Hope that helps
"If you can't be a good example, then you'll just have to serve as a horrible warning."