Honeybees, Apis mellifera, are eusocial insects with a well developed reproductive division of labour between the queen and the workers. The honeybee colony can be exploited by a wide range of parasites. Honeybee parasites may also become invasive species and can cause considerable damage to local ecosystems and agriculture. However, the successful treatment and control of such invasive species requires not only comprehensive information about the biology of the parasite itself but also a good understanding of the parasites' interactions with their hosts. In this thesis two recent examples of invasive honeybee parasites were investigated: 1) The small hive beetle, Aethina tumida (Coleoptera: Nitidulidae), is native to sub-Saharan Africa, where it is a minor pest only. In contrast, the beetles can be harmful parasites of European host subspecies in their new ranges (USA 1996, Egypt 2000, Australia 2002). Field and laboratory studies on the beetles and on European and African host colonies were carried out. The literature on the biology and the current distribution of the small hive beetle is reviewed and potential reasons for the difference between pest severity are discussed. Small hive beetles have the potential to become a global threat to apiculture and wild bee populations. 2) The Cape honeybee, A. m. capensis, is native to the Eastern and Western Cape provinces of South Africa and is characterized by a unique set of traits related to worker reproduction. Laying Cape honeybee workers can become social parasites in colonies of other honeybee subspecies. In 1990, the transport of A. m. capensis colonies into the northern provinces of South Africa had striking consequences for beekeeping with the neighbouring subspecies A. m. scutellata. Some pre-adaptations and mechanisms of the social parasitism by Cape honeybee workers, such as thelytoky and the development of pseudoqueens, are long known. In contrast, several proximate aspects of the social parasitic pathway are poorly understood. Likewise, the possibility of the evolution of a queenless social parasitic honeybee has also not been considered yet. Laboratory and field studies on socially parasitic workers and host colonies were carried out. In two articles the literature on socially parasitic workers is reviewed. This enables further insight into the proximate and ultimate aspects of the social parasitic pathway of A. m. capensis workers.