LAFAYETTE (CBS SF) — Africanized honeybees, also known as ‘killer bees’ have been found in the East Bay for the first time.

Africanized bees are a hybrid of the European bee and the African bee, and known for their more aggressive nature. They are smaller in size than European bees.

READ MORE: UPDATE: Pleasant Hill In-N-Out Burger Fined Over Vaccine Verifications; Dispute Follows SF Flap

Scientists located the bees in the Reliez Valley, a subdivision of Lafayette, in samples taken in 2014. Their findings were published in the September issue of the journal Plos One.

According to the report, Africanized bees first appeared in the United States in Texas back in 1990. The bees were first found in California around San Diego County in 1994, and since then have expanded their range as far north as the Sacramento River Delta.

READ MORE: UPDATE: Judge Won't Delay Case Against Los Gatos Mom Accused of Hosting Drunken Teen Sex Parties

Author Joshua Kohn, a professor of biology at UC San Diego has been traveling through the state to see how far north the bees have moved. His team discovered the colony near the southeast side of Briones Regional Park. Kohn believes they’ve migrated north due to the warm weather and drought conditions.

He told the San Francisco Chronicle humans should not be too worried because Africanized bees only attack when their hives are disturbed.

“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,” said Kohn.

MORE NEWS: Elizabeth Holmes' Defense Tries To Pick Apart Damaging Testimony From Theranos Project Manager

He said if they approach, run as quickly as possible and try to outdistance the bees. Africanized bees don’t usually go more than a quarter mile from their hives. Don’t attempt to swat or crush them. That will only make them more aggressive.