Many factors led to the situation in which we fear the appearance of yet another exotic microbe simply demonstrating our vulnerability to new invaders and the shrinking of the globe. Beside the tremendous increase in international travel and trade, climatic changes are a crucial factor for exotic arboviruses to establish endemic transmission cycles in Europe. Certain temperatures, humidity and--at least for mosquitoes--suitable water bodies are required for the respective species to develop and become abundant. Increasing temperatures reduce the overall time of the mosquito life cycle because the aquatic developmental stages are completed faster, and secondly, the time span required for the mosquito to be capable to transmit the acquired arbovirus to another susceptible host is shortened. Thus the chances for an exotic arbovirus to establish an autochtonous transmission cycle are increasing. Here, a review is provided on the known factors that determine vector competence for mosquitoes and a particular arbovirus. The comparison of the closely related West Nile and Usutu viruses in Europe and North America further demonstrates how different and unpredictable the epidemiology of such arboviruses can be. Time will answer the question on who is going to be the next arboviral intruder into Europe. But it is today that we can bring ourselves into a good position to conquer the next "alien" by setting up interdisciplinary networks to promote research on these "exotic" and thus neglected pathogens thereby enhancing our understanding on their transmission and the factors and mechanisms required for this.