In the apiary of Assiut University, the oriental hornets, Vespa orientalis L., were trapped and collecting every three days by using modified wooden traps to know their fluctuation and population during their active season. Also, detect the differences on the morphology, ultra-structure, and behavior between the different casts (queen, daughter worker and male) of V. orientalis. In the present study, the fluctuation showed that hornet population began with a slight increase number during September which comprised about (12.3%). In October, a big jump occurred (52.5 %) in their number. By the first week of November, the number started to decrease (26.7%) and then disappeared at the second fortnight of November. Antenna plays an important and vital role during host finding and acceptance behavior in insect life. Like many insects, oriental hornet Vespa orientalis L., use antennal chemo-receptors to detect the hosts during its active seasons. Scanning electron microscope (SEM) studies showed five types of sensilla (Chaetica, trichoidea, basiconica, placodea and coeloconica) were distributed on the antenna of the three different casts of the hornet. These function of sensillae possibly as chemo-, and tactile receptors, responding to movements of the antennae.