Africanized Honey Bee
Africanized honey bees (AHB), known colloquially as "killer bees" or Africanized bees, are hybrids of the African honey bee, Apis mellifera scutellata (not A. m. adansonii see Collet et al., 2006), with various European honey bees such as the Italian bee A. m. ligustica and A. m. iberiensis. These bees are relatively aggressive compared to the European subspecies. Small swarms of AHBs are capable of taking over European honey bee hives by invading the hive and establishing their own queen after killing the European queen.
In areas of suitable temperate climate, the survival traits of africanized queens and colonies outperform western honey bee colonies. This competitive edge leads to the dominance of African traits. In Brazil, the africanized hybrids are known as Assassin Bees, for their habit of taking over an existing hive of European bees; this habit is most evident when the hive being attacked has a weakened queen, so not all hives are equally vulnerable, and overall rates of hive usurpation can reach 20%.
All of the above information came from Wikipedia, the free encyclopedia