0
by giving pollen and nectar
Pollen
Pollen is a powdery substance produced by plants and can be found on the stamens inside their flowering bodies.
according to this source, Cleveland, OH has the lowest pollen counts of a "midwest" city.
http://www.allergydiagnostics.com/news.htm
the pollen might stick to their clothes, hands/fingers and hair, which can be an easy source to find out where the person has been.