SAN FRANCISCO (CBS/AP) – Researchers say Africanized honeybees, known as killer bees, have made their way to the Bay Area for the first time.

The San Francisco Chronicle reports the bees have been spotted in Lafayette near Briones Regional Park by UC San Diego researchers who have been tracking their movement in the state. The bees had previously only been observed as far north as Mariposa County.

It is not clear how many of the bees have moved into the area, but researchers say there is likely more than one colony.

The Africanized honeybee is a hybrid of the European bee and the African bee. The hybrids are known for their aggression toward perceived threats to their hives. According to a University of California fact sheet, they sting in large numbers, can sense a threat from people or animals 50 feet or more from nest, they will pursue an enemy 1⁄4 mile or more, and swarm frequently to establish new nests.

Researchers say the bees may have traveled farther north because of recent warmer weather conditions.

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