Africanized Honey Bee Facts

History and spread

From Brazil to Blythe: how Africanized bees reached California

Africanized bees are hybrids of African and European honey bees. They descend from African queens brought to Brazil for a breeding program in the 1950s.

1. In 1956, scientists imported 47 queens of Apis mellifera scutellata into São Paulo, Brazil, for breeding experiments. (Source: Zarate et al., California Agriculture, 2023)
2. African queens escaped from a researcher's program in Brazil in 1957, according to Texas A&M's Texas Apiary Inspection Service. (Source: Texas A&M Texas Apiary Inspection Service)
3. Africanized bees reached Mexico by 1985, Texas by 1990 and California by 1994. (Source: Kono & Kohn, PLOS ONE, 2015)
4. UC Riverside lists the first discovery in each state as Texas (October 1990), Arizona (June 1993), New Mexico (October 1993), California (October 1994) and Nevada (April 1999). (Source: UC Riverside Department of Entomology, Africanized Honeybees page, updated 2022)
5. UC Davis reported in November 1994 that the first California find was at Chuckwalla Valley State Prison, west of Blythe, and that those bees were an almost pure African strain. (Source: UC Davis News, 1994)
6. By May 1998, the CDFA colonized area covered all of Imperial County and parts of Riverside, San Bernardino and San Diego counties, about 18,140 square miles. (Source: CDFA, Detection Advisory PD03-98, 1998)
7. The first naturally migrating Africanized swarm in Los Angeles County was found on November 23, 1998, beside Manhattan Beach Boulevard in Lawndale. (Source: CDFA, Detection Advisory PD04-99, 1999)
8. Africanized foragers were found in Orange County for the first time on March 1 to 3, 1999, in Costa Mesa, Garden Grove, La Palma and Seal Beach. (Source: CDFA, Detection Advisory PD17-99, 1999)
9. By 2005, the colonized area was about 63,303 square miles, including all of Imperial, Kern, Kings, Los Angeles, Orange, Riverside, San Bernardino, San Diego, Tulare and Ventura counties. (Source: County of Santa Clara Agriculture, Africanized Honeybee page)
10. UC Riverside's Center for Invasive Species Research reported that by 2008 Africanized bees had colonized all southern California counties and the southern Central Valley. (Source: UC Riverside Center for Invasive Species Research)
11. In Texas, Africanized bees had been detected in 163 of the state's 254 counties by August 2006. (Source: Texas A&M Texas Apiary Inspection Service)
12. In 2005, Africanized bees were found for the first time in Louisiana, Arkansas and Florida; Florida had found them in 14 counties. (Source: USDA Agricultural Research Service, news release, 2006)

Sources differ on 1956 versus 1957 for Brazil. USDA ARS (2004) says the bees were brought to Brazil in 1956 and reached the Brazilian wilds in 1957. Published spread rates also differ: 160 to 500 km per year (California Agriculture, 2023), 300 to 500 km per year (UC San Diego, 2015) and 200 to 300 miles per year (UF/IFAS; County of Santa Clara). The colonized-area figures come from official advisories at different times and are not a continuous series.

Genetics

What Southern California's Africanized bees are made of

Genetic studies show that Southern California's wild honey bees are mixed hybrids, with less African ancestry than bees in Mexico and Central America.

1. In a UC San Diego study, 64.8% of 298 foraging bees sampled across San Diego County carried African mitochondria. (Source: Kono & Kohn, PLOS ONE, 2015)
2. By wing and body measurements, 60.85% of the San Diego County bees in that study were classed as African. (Source: Kono & Kohn, PLOS ONE, 2015)
3. In the same study, 7 of 10 feral colonies carried the African mitotype, compared with 3 of 24 managed hives (12.5%). (Source: Kono & Kohn, PLOS ONE, 2015)
4. North of San Diego County, 23 of 265 bees from 91 sites (8.7%) carried African mitochondria. (Source: Kono & Kohn, PLOS ONE, 2015)
5. UC San Diego summarized the findings as more than 60 percent of San Diego County foragers having Africanized traits, versus only 13 percent of managed or commercial hives. (Source: UC San Diego news release, September 11, 2015)
6. Zárate and colleagues analyzed the nuclear and mitochondrial ancestry of 60 bees from Panama, Costa Rica, Mexico and San Diego. (Source: Zárate et al., Ecology and Evolution, 2022)
7. San Diego bees carried mitochondria from all four major honey bee lineages, while nearly all Central American and Mexican bees carried African mitochondria. (Source: Zárate et al., Ecology and Evolution, 2022)
8. A 2023 review estimated that feral bees in Southern California carry about 40% A. m. scutellata genomic content, roughly half that of hybrids in Mexico, Central America, Texas or Arizona. (Source: Zarate et al., California Agriculture, 2023)
9. A UC Davis genome study published in PLOS Genetics in October 2020 sequenced hundreds of bees and found African ancestry declines across hundreds of miles of latitude. (Source: UC Davis News, 2020 (Calfee et al., PLOS Genetics))
10. UC Riverside researchers tracked 236 colonies from 2019 to 2022, 101 headed by Southern California hybrid queens and 135 by commercial queens. (Source: Chong-Echavez & Baer, Scientific Reports, 2026)
11. Colonies with the local hybrid queens had about 68% fewer Varroa mites on average than colonies with commercial queens. (Source: UC Riverside news release, April 10, 2026)
12. UC Riverside describes the hybrid population as carrying ancestry from four lineages: African, Eastern European, Middle Eastern and Western European. (Source: UC Riverside news release, April 10, 2026)

The Kono and Kohn paper reports 23 managed hives in its methods and 24 in its results; the UC San Diego release rounds the managed-hive share to 13%. Mitochondrial tests trace only the mother's line, so a bee can carry African mitochondria with mostly European nuclear genes, which is why the 2015 (mitochondrial) and 2022 (nuclear) figures differ. The UC Riverside mite study measured mite loads, not defensiveness.

Behavior

How Africanized bees behave compared with European bees

The main difference is defense. Individual Africanized bees are not more dangerous; colonies send out far more defenders, react to smaller disturbances and stay agitated longer.

1. A European colony may send 10 to 20 guard bees in response to disturbances up to 20 feet away; an African colony may send several hundred in response to disturbances up to 120 feet away. (Source: UF/IFAS Extension, ENY-147, 2015)
2. Once agitated, European colonies usually calm down within 10 to 15 minutes, while African colonies can stay defensive for hours. (Source: UF/IFAS Extension, ENY-147, 2015)
3. Africanized bees inflict about ten times as many stings per encounter as European honey bees. (Source: County of Santa Clara Agriculture; San Bernardino County Environmental Health Services)
4. UC Cooperative Extension says Africanized bees can detect people or animals 50 feet or more from the nest and sense power-equipment vibrations 100 feet or more away. (Source: UC ANR Publication 8068, 2002)
5. Africanized bees may chase an intruder a quarter mile or more. (Source: UC ANR Publication 8068, 2002; UC Cooperative Extension San Diego)
6. European honey bees swarm 1 or 2 times a year; African honey bees can swarm 10 or more times a year. (Source: UF/IFAS Extension, ENY-147, 2015)
7. USDA ARS says a European colony typically swarms once every 12 months, while an Africanized colony may swarm as often as every six weeks in swarm season. (Source: USDA ARS Carl Hayden Bee Research Center, updated 2021)
8. African colonies abscond, completely abandoning the nest, during times of dearth or repeated disturbance; European colonies rarely do. (Source: UF/IFAS Extension, EENY-429, rev. 2025; ENY-147, 2015)
9. European bees nest in cavities of about 10 gallons, while African bees use smaller cavities of 1 to 5 gallons. (Source: UF/IFAS Extension, ENY-147, 2015)
10. Reported Africanized nest sites include water meter boxes, overturned flower pots, old tires, lumber piles, holes in fences and the ground, and spaces under low decks. (Source: UC Riverside Department of Entomology; UC ANR Publication 8068, 2002)
11. A 2023 review notes that no quantitative California study has yet compared defensiveness between local hybrids and European bees. (Source: Zarate et al., California Agriculture, 2023)
12. In San Diego County, feral hybrids accounted for 75% of flower visits to native vegetation and over 90% of visits to the most abundant wildland blooms. (Source: Zarate et al., California Agriculture, 2023)

Pursuit distances vary by source: UF/IFAS gives a 120-foot response distance, UC sources and San Bernardino County cite a quarter mile, and the San Diego County Department of Agriculture advises running until bees stop following, up to half a mile.

Identification

How to tell Africanized bees: you can't by eye

Africanized and European honey bees look the same in the field. Identification takes lab measurements or DNA tests.

1. UC Riverside says Africanized bees can be distinguished from European bees by measurements under a microscope and by DNA analysis. (Source: UC Riverside Department of Entomology)
2. UF/IFAS describes morphometric analysis of wing veins and body parts as the first round of identification, with genetic analysis giving a more rigorous answer, especially for hybrids. (Source: UF/IFAS Extension, EENY-429, revised 2025)
3. Morphometric analysis was first used to separate Africanized from European bees in South America in 1978. (Source: UF/IFAS Extension, EENY-429, revised 2025)
4. The Fast Africanized Bee Identification System (FABIS), developed by Sylvester and Rinderer in 1987, screens bees by weight, forewing length and hind femur length. (Source: Ohio State University Extension, Buckeye Yard & Garden onLine)
5. FABIS uses the forewings of 10 bees; in one Ohio State case, an average forewing length of 9.27 mm was above the 9.001 mm critical value, so the colony was classed as European. (Source: Ohio State University Extension, Buckeye Yard & Garden onLine)
6. The 1998 CDFA confirmation of Africanized bees in San Bernardino County used mitochondrial DNA analysis. (Source: CDFA, Detection Advisory PD03-98, 1998)
7. UC extension apiculturist Eric Mussen described three identification criteria: mitochondrial DNA (used by CDFA), morphometrics and isozymes. (Source: UC ANR, Bug Squad blog)
8. The USDA ARS Carl Hayden Bee Research Center says it can no longer analyze honey bee identification samples by morphometrics. (Source: USDA ARS Carl Hayden Bee Research Center)
9. UC Riverside advises that all honey bees not under a beekeeper's care should be treated as Africanized. (Source: UC Riverside Department of Entomology)

Behavior is not proof either way. In an Ohio State case, a colony its beekeeper described as aggressive was classed as European by FABIS. Hybrid bees can test differently depending on whether a lab measures wings, mitochondrial DNA or nuclear DNA.

Stinging incidents

Killer bees in California: documented deaths and incidents

Deaths from Africanized bee attacks in the United States are rare and poorly counted. The figures below are the documented ones I could find.

1. UC Riverside's list of U.S. deaths from Africanized bee stings runs from an 82-year-old man in Texas in August 1993 to an 83-year-old man in Long Beach, California, in September 1999 who received about 50 stings. (Source: UC Riverside Department of Entomology)
2. One death on the UC Riverside list, an 88-year-old woman in Phoenix in October 1995, involved more than 1,000 stings. (Source: UC Riverside Department of Entomology)
3. A 2009 Texas A&M paper, citing earlier work (McKenna and Hess, 2003), says at least 18 U.S. deaths have been related to massive numbers of stings, and that the true number is likely higher. (Source: Pankiw, Journal of Medical Entomology, 2009)
4. The same paper reported at least 212 confirmed stinging incidents in Texas from 1991 to 1993. (Source: Pankiw, Journal of Medical Entomology, 2009)
5. As of May 1998, CDFA reported no human fatalities from Africanized bees in California; Imperial County recorded its first animal death, a dog, that month. (Source: CDFA, Detection Advisory PD03-98, 1998)
6. On July 3, 2017, a 49-year-old date palm worker in California died after being stung by numerous bees from hives hidden in the palms; investigators did not know which strain was involved. (Source: CDPH, FACE Report 17CA003, 2018)
7. Since hybrid bees arrived in the Americas, more than 1,000 human deaths have been associated with honey bee attacks, mostly in Central and South America. (Source: Zarate et al., California Agriculture, 2023)
8. Venezuela attributed at least 70 deaths to Africanized bees from 1978 to 1981. (Source: Pankiw, Journal of Medical Entomology, 2009)

No agency publishes a current national count of Africanized bee deaths. The UC Riverside list stops in 1999, and the 2009 count of 18 covers deaths from mass stinging, not only confirmed Africanized cases. The 2017 California worker death was not confirmed as Africanized, and the worker was allergic to bee stings.

Climate limits

Why Africanized bees stopped spreading north

Cold winters and, possibly, heavy year-round rain appear to limit where Africanized bees can live.

1. That 2015 detection was about 250 km northwest of the previously reported limit in Mariposa County, recorded in 2006. (Source: Kono & Kohn, PLOS ONE, 2015)
2. The 2015 study's authors concluded that northward expansion has slowed considerably from maximal rates. (Source: Kono & Kohn, PLOS ONE, 2015)
3. A 2023 review places the northern limit of African ancestry in California in Napa and Sacramento counties. (Source: Zarate et al., California Agriculture, 2023)
4. UC Davis researchers reported in 2020 that bees with majority African ancestry are unable to survive colder winters. (Source: UC Davis News, 2020)
5. In South America, African bees have failed to establish below about 32° south latitude. (Source: UF/IFAS Extension, EENY-429, revised 2025)
6. USDA ARS entomologist José Villa found that annual rainfall above 55 inches, spread evenly through the year, correlated with an almost complete barrier to spread, though cause and effect was not confirmed. (Source: USDA Agricultural Research Service, news release, 2004)

The rainfall finding is a correlation reported in a 2004 USDA news release, not a proven cause. Southern California's dry climate is well below that rainfall level, so it does not limit the bees here.

Management

How beekeepers and property owners manage Africanized bees

Beekeepers in Africanized areas mostly manage the queen. Property owners reduce risk by closing off the small spaces these bees like to nest in.

1. UC Cooperative Extension in San Diego says a managed hive that suddenly turns much more defensive has a good probability of having been taken over by Africanized bees, and will have to be requeened. (Source: UC Cooperative Extension San Diego, Africanized Honey Bees page)
2. UF/IFAS notes some beekeepers in African bee areas requeen colonies with European queens, and that managing African colonies has been discouraged in the U.S. (Source: UF/IFAS Extension, EENY-429, revised 2025)
3. UC Riverside says well-kept managed European colonies help defend against Africanized bees through competition and genetic dilution. (Source: UC Riverside Department of Entomology)
4. UC Cooperative Extension advises sealing openings larger than 1/8 inch and covering vents and utility box openings with 1/8-inch hardware cloth. (Source: UC ANR Publication 8068, 2002)
5. The same publication advises checking for bee activity once or twice a week from spring to fall. (Source: UC ANR Publication 8068, 2002)
6. After the 2017 date palm death, CDPH advised employers to conduct a hazard assessment of the work area before work begins and to have a bee removal service remove any hive or nest found. (Source: CDPH, California FACE Fact Sheet No. 28, 2018)

Public safety

What to do if Africanized bees attack

Public agencies give consistent advice: get away fast, protect your face, and get inside a car or building.

1. UC Riverside advises getting away and sheltering in a car or building even if bees follow, and not jumping into water because bees will still be there when you come up. (Source: UC Riverside Department of Entomology)
2. UC Cooperative Extension says water or thick brush does not give enough protection, and advises protecting your face and eyes while leaving. (Source: UC ANR Publication 8068, 2002)
3. San Diego County advises running by a direct route until the bees stop following, which can be up to half a mile. (Source: San Diego County Department of Agriculture, Weights and Measures)
4. San Bernardino County advises running in a straight line, not standing still or hiding in a hole, and not slapping at bees. (Source: San Bernardino County Environmental Health Services)
5. San Bernardino County advises scraping stingers off with a fingernail or dull knife rather than squeezing them with tweezers or fingers. (Source: San Bernardino County Environmental Health Services)
6. UC Cooperative Extension says a stinger pumps most of its venom in the first minute, so it should be removed quickly. (Source: UC ANR Publication 8068, 2002)
7. UC Riverside lists people allergic to stings, the young, the elderly, the disabled, and confined pets or livestock as facing the greatest danger. (Source: UC Riverside Department of Entomology)
8. CDPH recommends that workers allergic to insect stings see a health care professional about an epinephrine auto-injector and carry it at all times. (Source: CDPH, FACE Report 17CA003, 2018)

This is general public guidance from the agencies named. UC ANR Publication 8068 and San Diego County advise seeking medical attention if breathing is troubled, if stung numerous times, or if allergic to bee stings.

Myths vs facts

Killer bee myths and what the research says

1. Myth: Africanized venom is stronger. Fact: both bee types use the same venom, and deaths usually result from the number of stings received. (Source: UF/IFAS Extension, EENY-429, revised 2025)
2. UF/IFAS puts a fatal dose of venom at about 10 stings per pound of body weight, from either bee type. (Source: UF/IFAS Extension, ENY-147, 2015)
3. Myth: one killer bee sting is worse. Fact: a single Africanized sting is no more painful or dangerous than one from any other honey bee. (Source: San Bernardino County Environmental Health Services)
4. Myth: they are bigger. Fact: they look nearly identical to European honey bees and are only slightly smaller. (Source: UC Riverside Department of Entomology; UF/IFAS Extension, EENY-429)
5. Myth: every swarm is dangerous. Fact: San Bernardino County says most swarms are not particularly defensive and will not chase a person, since they have no hive to defend. (Source: San Bernardino County Environmental Health Services)
6. UC Riverside says the 'killer bee' label refers to increased defensive behavior, not to the bee itself. (Source: UC Riverside Department of Entomology)
7. Like other honey bees, each Africanized worker can sting only once. (Source: UC ANR Publication 8068, 2002)

Questions

Frequently asked questions

Keep reading

Related on this site

• Africanized “killer” bees in SoCal: how to tell and what to do
• Emergency bee removal
• Live bee relocation

How this page was made

Methodology & sources

Every fact on this page was traced to a primary source (a government data release, a university research or extension publication, a professional medical body or a peer-reviewed paper) and checked against the original document. Data years are given where they differ from publication years. Where reputable sources disagree, both figures are shown. Sources are named in plain text next to each fact.

• California Department of Food and Agriculture (CDFA) detection advisories
• Kono & Kohn, PLOS ONE, 2015
• UC San Diego news release, 2015
• Zárate et al., Ecology and Evolution, 2022
• Zarate et al., California Agriculture, 2023
• Chong-Echavez & Baer, Scientific Reports, 2026
• UC Riverside news release, 2026
• UC Riverside Department of Entomology
• UC Riverside Center for Invasive Species Research
• UC Davis News
• UC ANR Publication 8068, BEE ALERT: Africanized Honey Bee Facts
• UC Cooperative Extension San Diego
• UC ANR Bug Squad blog
• UF/IFAS Extension ENY-147 and EENY-429
• USDA Agricultural Research Service
• USDA ARS Carl Hayden Bee Research Center
• Texas A&M Texas Apiary Inspection Service
• Pankiw, Journal of Medical Entomology, 2009
• Ohio State University Extension
• California Department of Public Health FACE Report 17CA003
• County of Santa Clara Agriculture
• San Bernardino County Environmental Health Services
• San Diego County Department of Agriculture, Weights and Measures