LAFAYETTE  (AP) — Africanized honeybees, known as killer bees because of their swarming, aggressive and deadly nature when a colony is threatened, have made their way to the San Francisco Bay Area for the first time, researchers say.

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 San Francisco Chronicle reportedTuesday.

The bees had previously been seen only as far north as Mariposa County.

Joshua Kohn, a professor of biology at UC San Diego, said it is hard to tell at this point how many of the bees are in the San Francisco area.

“The sampling is a little sparse up north,” he told the newspaper. “But there is most likely more than one colony,” he said.

Kohn said honeybees normally forage within about a mile of their hive, though they can go up to about 5 miles.

The Africanized honeybee is a hybrid of the European bee and the African bee.

While the bees can pose a threat to humans, Kohn said, people should not be too concerned.

“An Africanized honeybee out foraging on flowers is no more aggressive than your average European honeybee. Nor is the sting of an individual any different,” he said. “It’s only when a hive is disturbed that the level of aggression from Africanized bees is elevated.”

Kohn said he has no way of knowing whether Africanized bees are in Lafayette permanently. But if they do stay, he said, there could be some benefits.

 The bees could represent a more stable species to replace rapidly dying European varieties.

“The Africanized bees are more resistant to one of the diseases related to colony collapse disorder in agriculture,” Kohn said.

The bees have been known to build their hives in trees, under rocks, within caves and under edges of man-made objects such as sheds or chimneys.

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

Brian Johnson, a honeybee researcher at UC Davis, said it’s important to remember the bees can pose danger.

A swarm of Africanized bees killed a construction worker and injured two others last month in Riverside as the workers graded land for a parking lot unaware that an underground vault housed a hive.

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