Bee Swarm Season 2027: What to Expect in Southern California

The biology

What drives a swarm season

Swarming is how a honey bee colony reproduces. It follows colony growth, and colony growth follows the flowers. So swarm timing moves with local bloom, and a wet or dry winter changes it.

1. Penn State Extension explains that a growing spring population triggers colonies to rear new queens and drones, the first step toward swarming. (Source: Penn State Extension, Honey Bee Management Throughout the Seasons, updated 2023)
2. In a larger, more congested colony, queen pheromone spreads less through the brood nest, and that weaker signal is linked to queen rearing, according to Penn State Extension. (Source: Penn State Extension, Honey Bee Management Throughout the Seasons, updated 2023)
3. Penn State Extension ties the spring build-up to bloom: flowering trees in spring provide substantial nectar and pollen that feed colony growth. (Source: Penn State Extension, Honey Bee Management Throughout the Seasons, updated 2023)
4. When a colony swarms, its size is reduced dramatically, by one-half or more, according to Penn State Extension. (Source: Penn State Extension, Honey Bee Management Throughout the Seasons, updated 2023)
5. UC IPM describes a departing swarm as the old queen and about half of the workers, a group that can contain 5,000 to 20,000 bees. (Source: UC IPM Pest Notes, Removing Honey Bee Swarms and Established Hives (Pub. 74159), 2012)
6. In a 7-year Cornell study of 33 wild nest sites around Ithaca, N.Y. (2010-2016), 87% of colonies had a queen turnover, probably by swarming, each summer. (Source: Seeley, Apidologie, 2017)
7. The same Cornell study found 97% of wild colonies survived summers, but only 23% of first-year (founder) colonies survived winter, compared with 84% of established colonies. (Source: Seeley, Apidologie, 2017)
8. Around Ithaca, 80% of swarms are produced between May 15 and July 15 and 20% between Aug. 15 and Sept. 15, the Cornell paper notes, citing earlier work by Fell and colleagues (1977). (Source: Seeley, Apidologie, 2017 (citing Fell et al., 1977))
9. Cornell's honey bee extension associate said in 2019 that most New York swarms occur between mid-May and mid-July, with some seen through September. (Source: Cornell University media tip sheet, May 2019)

The Cornell figures come from New York, where winters are cold and swarming starts in mid-May. They describe the biology; Southern California timing is different. Here, mild winters and earlier bloom move the season forward, as the next section shows.

Local timing

When swarm season runs in Southern California

Local agencies put the busiest stretch in spring. Because Southern California winters are mild, colonies keep raising brood through winter and are ready to swarm early.

1. The Los Angeles County Agricultural Commissioner says that during April, May and June, many honey bee colonies swarm. (Source: Los Angeles County Agricultural Commissioner/Weights and Measures, Nuisance Bee Complaints)
2. UC ANR's San Diego County beekeeping program says swarming in the Central, Southern and Western states generally occurs from March to June, though it can occur at almost any time from April to October. (Source: UC ANR, Beekeeping in San Diego County: Bee Biology and Behavior)
3. UC Davis apiculturist Eric Mussen described swarms as leaving mostly in the spring, but sometimes in late summer. (Source: UC Davis Laidlaw Facility, Honey Bee Swarms)
4. UC IPM says swarming happens usually in the spring but sometimes at other times of the year when local conditions permit. (Source: UC IPM Pest Notes, Pub. 74159, 2012)
5. Under mild winter conditions like Southern California's, egg laying and brood rearing are usually not affected by winter, according to UC ANR. (Source: UC ANR, Beekeeping in San Diego County: Bee Biology and Behavior)
6. UC ANR notes that in early winter the queen increases drone production, in preparation for colony swarming. (Source: UC ANR, Beekeeping in San Diego County: Bee Biology and Behavior)
7. UC ANR says the colony reaches peak population in early summer, but in arid Southern California a reduced supply of nectar and pollen is available in summer. (Source: UC ANR, Beekeeping in San Diego County: Bee Biology and Behavior)
8. Hive populations diminish in fall as the amount of nectar and pollen collected drops, according to UC ANR. (Source: UC ANR, Beekeeping in San Diego County: Bee Biology and Behavior)
9. Los Angeles County says about one-third of the workers leave with a queen when a colony divides, and that swarms left alone usually leave in two to three days, sometimes within a few hours. (Source: Los Angeles County Agricultural Commissioner/Weights and Measures, Nuisance Bee Complaints)
10. UC IPM says a resting swarm's scouts usually reach a consensus on a new home within a few hours to a few days. (Source: UC IPM Pest Notes, Pub. 74159, 2012)

Sources differ on two points. On timing, the UC ANR March-to-June range covers the Central, Southern and Western states as a group, while Los Angeles County names April to June. On swarm size, UC sources say about half of the workers leave; Los Angeles County says about one-third. Both are rough figures and real swarms vary.

Swarm calendar

Month-by-month swarm calendar for Southern California

This calendar describes a typical year. It is built from the UC, county and federal sources on this page. Exact timing shifts with rain, temperature and bloom in your neighborhood.

The 'what homeowners tend to see' column restates the sourced biology in plain terms. It is a general guide and is not based on a measured count of swarm calls by month.

Rain to swarms

How winter rain becomes spring swarms

The chain is easy to describe and hard to measure. Winter rain feeds spring bloom, bloom feeds brood rearing, and crowded, growing colonies swarm. I found no source that measures swarm counts against rainfall in Southern California, so the link explains the direction of the effect but cannot predict a number.

1. Before the 2017 desert superbloom, 6.11 inches of precipitation fell across California's Southeast Desert Basins in winter 2016-17, more than 200% of the division's normal 2.97 inches. (Source: NOAA climate.gov, 2017)
2. NOAA's climate.gov describes desert wildflower seeds waiting years, then sprouting after unusually heavy or frequent fall and winter rains. (Source: NOAA climate.gov, 2017)
3. UC Riverside ecologist Cameron Barrows described the 2019 bloom season as following a regular series of soaking rains from October through February. (Source: UC Riverside News (university news release), March 2019)
4. UC Riverside earth sciences professor Richard Minnich said wildflowers 'just wait for their moment,' with the best blooms usually in the first wet year after a long drought; the release adds that wildflower seeds can survive decades or longer. (Source: UC Riverside News (university news release), March 2019)
5. Minnich cautioned that a wet year does not guarantee a lot of flowers, because invasive European annual grasses such as bromes compete with wildflowers. (Source: UC Riverside News (university news release), March 2019)
6. The UC Riverside release itself (not a quoted researcher) states that a tight relationship exists between the annual bloom and bee populations. (Source: UC Riverside News (university news release), March 2019)
7. UC Riverside entomologist Hollis Woodard said bees need a consistent supply of flowering plants across years to build up their populations. (Source: UC Riverside News (university news release), March 2019)
8. California has over 1,600 bee species, per the UC Riverside release, and UCR museum scientist Doug Yanega said about 500 native bee species live within 50 miles of Riverside. (Source: UC Riverside News (university news release), March 2019)

The UC Riverside figures come from a 2019 university news release quoting researchers; they have not been published in a peer-reviewed study. Superbloom data mostly describe desert wildflowers; urban and suburban bees also forage on irrigated gardens, so city bloom tracks rain less closely.

2027 outlook

El Niño 2027 and the swarm outlook: what the official forecast says

Nobody forecasts swarms directly. Rain can be forecast, but only as odds. As of NOAA's Oct. 8, 2026 ENSO discussion and Oct. 15, 2026 winter outlook, a strong-to-very strong El Nino is likely through January-March 2027, and the December-February outlook favors wetter-than-average conditions across the southern tier, including much of California. If that rain arrives, the sourced mechanisms point to a busier spring 2027 swarm season. If it does not, expect a typical or quieter one. This outlook will change as NOAA updates its forecasts.

1. As of Oct. 8, 2026, NOAA's Climate Prediction Center had an El Nino Advisory in effect. (Source: NOAA Climate Prediction Center, ENSO Diagnostic Discussion, Oct. 8, 2026)
2. The Niño-3.4 sea surface temperature index stood at +2.1°C in the Oct. 8, 2026 CPC discussion. (Source: NOAA Climate Prediction Center, ENSO Diagnostic Discussion, Oct. 8, 2026)
3. CPC's Oct. 8, 2026 synopsis: 'El Niño continues to strengthen, with a strong-to-very strong El Niño likely through January-March 2027 (remaining greater than an 83% chance).' (Source: NOAA Climate Prediction Center, ENSO Diagnostic Discussion, Oct. 8, 2026)
4. CPC put the chance of a historic event (a 3-month Relative Oceanic Niño Index of +2.5°C or more, exceeding any El Nino since 1950) at 54% for September-November, 83% for October-December and 70% for November-January 2026-27. (Source: NOAA Climate Prediction Center, ENSO Diagnostic Discussion, Oct. 8, 2026)
5. CPC also wrote that with an event of this magnitude, the chances of experiencing impacts consistent with El Nino are larger, though not guaranteed. (Source: NOAA Climate Prediction Center, ENSO Diagnostic Discussion, Oct. 8, 2026)
6. NOAA's Oct. 15, 2026 winter outlook for December 2026 to February 2027 says wetter-than-average conditions are most likely across the southern tier, from the Southwest to the Southeast. (Source: NOAA, U.S. Winter Outlook news release, Oct. 15, 2026)
7. NOAA's Oct. 15, 2026 outlook forecasts drought conditions to improve or end in the Southwest. (Source: NOAA, U.S. Winter Outlook news release, Oct. 15, 2026)
8. CPC's Oct. 15, 2026 discussion shows an elevated likelihood of above-normal seasonal precipitation for much of California and the Southwest in November-January. (Source: NOAA Climate Prediction Center, 90-day prognostic discussion, Oct. 15, 2026)
9. CPC added that its wet-side probabilities for the West Coast and Southwest are somewhat lower than for the Southeast. (Source: NOAA Climate Prediction Center, 90-day prognostic discussion, Oct. 15, 2026)
10. A September 2026 Southern California drought outlook pilot using NOAA data says very strong El Nino events usually bring above-average rain to Southern California, mostly from heavy storms between December and March. (Source: NOAA/NIDIS, Southern California Sector-Specific Drought Outlook Pilot, Sept. 2026)
11. A 2015 NOAA study found the strongest El Ninos greatly increase the likelihood of above-average precipitation statewide, while moderate events raise it only over Southern California. (Source: NOAA Physical Sciences Laboratory news, Dec. 2015 (Hoell et al.))
12. During the strong 2015-16 El Nino, Southern California's seasonal precipitation came in 32% below normal, a result researchers called a surprise. (Source: Zhang et al., Journal of Climate, 2018)
13. NOAA's ENSO blog notes that the 2015-16 winter forecast was widely panned as a bust for California. (Source: NOAA climate.gov ENSO blog, Nov. 2023)

Seasonal outlooks give odds and can miss. The odds above are from CPC's Oct. 8, 2026 ENSO discussion (its Oct. 15 seasonal discussion cites about 80% for at least a strong El Nino through January-March) and NOAA's Oct. 15, 2026 winter outlook. CPC's next ENSO discussion is scheduled for Nov. 12, 2026, and NOAA's next outlook update for Nov. 19. The 2015-16 winter shows a strong El Nino can still leave Southern California dry. I will update this page as the rain season goes on.

Rain so far

Rainfall so far this season

The rain season has only started, but October 2026 ran wet across the region. Riverside, closest to my Inland Empire service area, got about six times its normal October rain.

1. Downtown Los Angeles recorded 1.19 inches of rain in October 2026, against a normal of 0.58 inches (+0.61 inches). (Source: National Weather Service Los Angeles/Oxnard, monthly climate summary, Oct. 2026)
2. Los Angeles International Airport recorded 0.86 inches in October 2026, against a normal of 0.49 inches. (Source: National Weather Service Los Angeles/Oxnard, monthly climate summary, Oct. 2026)
3. Riverside Municipal Airport recorded 2.00 inches in October 2026, against a normal of 0.33 inches (+1.67 inches). (Source: National Weather Service San Diego, monthly climate summary, Oct. 2026)
4. San Diego International Airport recorded 1.68 inches in October 2026, against a normal of 0.50 inches, with 8 days of measurable rain versus a normal of 2.4. (Source: National Weather Service San Diego, monthly climate summary, Oct. 2026)
5. October 2025, by comparison, brought 0.61 inches to Riverside and 1.41 inches to downtown Los Angeles, per the same NWS summaries. (Source: National Weather Service San Diego and Los Angeles/Oxnard, monthly climate summaries, Oct. 2026)

October is a small share of the rain year, and one wet month does not make a wet winter. NWS data are preliminary. I could not get a current season-to-date (since July 1 or Oct. 1) total for these stations, so only the October figures are shown.

Colony counts

How many colonies are going into 2027

Swarms come from colonies, so the number of colonies matters. Most of these figures cover managed colonies; wild and feral colonies in walls and trees are not counted by USDA.

1. California had 885,000 honey bee colonies (operations with five or more) on Jan. 1, 2026, down from 910,000 on Jan. 1, 2025. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
2. California operations lost 220,000 colonies, or 18%, in January-March 2026, up from 150,000 (12%) in the same quarter of 2025. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
3. In April-June 2026, California lost 89,000 colonies (11%), compared with 80,000 (10%) a year earlier. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
4. Nationally, colonies on Jan. 1, 2026 totaled 2.81 million, up 6% from Jan. 1, 2025. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
5. U.S. colony losses in January-March 2026 were 454,890 colonies, or 16%, up from 12% in January-March 2025. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
6. The U.S. Beekeeping Survey estimated annual colony losses of 39.9% for April 2025 to April 2026, down from 55.6% in 2024-25. (Source: Auburn University, U.S. Beekeeping Survey release, June 2026)
7. The same survey put 2025-26 winter losses at 30.3%. (Source: Auburn University, U.S. Beekeeping Survey release, June 2026)
8. More than 2,300 beekeepers managing 219,000 colonies answered the 2025-26 survey. (Source: Auburn University, U.S. Beekeeping Survey release, June 2026)

The two loss measures point in different directions. The U.S. Beekeeping Survey shows annual losses easing to 39.9% in 2025-26 from 55.6%, while USDA NASS shows first-quarter 2026 losses higher than in 2025. They measure different periods, beekeepers and methods. NASS also revises earlier quarters; this page uses the figures in its August 2026 report. Neither tracks feral colonies, which produce many of the swarms homeowners see.

Almond season

Almond pollination and California's bees

Every February, beekeepers from across the country truck colonies into California for the almond bloom. It is the largest pollination event in the country, and it shapes California's colony numbers each winter.

1. California's almond pollination season generally starts around Feb. 10 and ends around March 10, according to UC Davis apiculturist Eric Mussen. (Source: UC ANR Bug Squad blog, 'White Gold' (quoting Eric Mussen, UC Davis))
2. Each almond acre requires two hives for pollination, per the same UC ANR source. (Source: UC ANR Bug Squad blog, 'White Gold')
3. University of Illinois economists estimated that about 1.4 million acres of almonds required about 2.7 million colonies for pollination in 2024. (Source: farmdoc daily, University of Illinois, Feb. 2025)
4. The same analysis estimated that February 2024 almond demand required virtually all (99%) of the colonies in the U.S. on Jan. 1, 2024. (Source: farmdoc daily, University of Illinois, Feb. 2025)
5. California's maximum colony count during January-March 2026 was 1,250,000, compared with 885,000 colonies on Jan. 1, as colonies were moved in for the bloom. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
6. In October-December 2025, California's maximum colony count reached 910,000, up from 520,000 on Oct. 1, 2025. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)
7. By April 1, 2026, California's count had fallen to 770,000 colonies. (Source: USDA NASS, Honey Bee Colonies report, Aug. 3, 2026)

Almond orchards are mostly in the Central Valley, and most of these colonies are managed hives that return to their beekeepers. I found no study measuring how the almond influx changes swarm numbers in Southern California neighborhoods, so this page makes no claim about it. The farmdoc estimates are university economists' calculations based on per-acre assumptions.

Africanized bees

Why Africanized bees stretch the swarm season

Africanized bees are established throughout Southern California, and UC says wild swarms and nests around San Diego are mainly Africanized. They swarm far more often than European bees and use smaller cavities, which may help explain why swarms and new nests show up outside the spring peak.

1. The California Department of Public Health says Africanized honey bees swarm 20 to 40 times more often than European honey bees. (Source: California Department of Public Health, Africanized Honeybees)
2. UF/IFAS says African honey bees can swarm 10 or more times a year, while European honey bees swarm 1 or 2 times per year. (Source: UF/IFAS Extension, Differences Between European and African Honey Bees (IN784))
3. UF/IFAS says African honey bees abscond (abandon the nest) often and relocate to better sites, while European bees rarely abscond. (Source: UF/IFAS Extension, IN784)
4. African honey bee swarms contain fewer bees and need a smaller cavity, typically about 1 to 5 gallons, compared with about 10 gallons for European colonies, per UF/IFAS. (Source: UF/IFAS Extension, IN784)
5. CDPH reports that Africanized bees were at California's southern border in October 1993 and are now established throughout Southern California. (Source: California Department of Public Health, Africanized Honeybees)
6. A UC publication says Africanized bees entered Southern California in 1994 and are established there and in the southern San Joaquin Valley. (Source: UC ANR Publication 8068, Bee Alert: Africanized Honey Bee Facts, 2002)
7. UC ANR's San Diego beekeeping program says the swarms and nests of wild bees around San Diego are mainly Africanized. (Source: UC ANR, Beekeeping in San Diego County: FAQs)
8. The County of San Diego advises residents to check once or twice a week from spring to fall for bees entering or leaving the same spot on a home or yard. (Source: County of San Diego Dept. of Agriculture, Weights and Measures, Bee Alert)
9. CDPH advises people not to attempt to remove a colony themselves. (Source: California Department of Public Health, Africanized Honeybees)

CDPH's '20 to 40 times more often' and UF/IFAS's '10 or more times a year' versus '1 or 2' are different ways of stating the gap and do not match exactly. Both agree Africanized bees swarm much more often. Neither gives a Southern California field count.

Questions

Frequently asked questions

Keep reading

Related on this site

• Will a bee swarm leave on its own?
• Bee swarm outside? What to do next
• Can one hive turn into multiple colonies?
• 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.

• NOAA Climate Prediction Center (ENSO Diagnostic Discussion; 90-day prognostic discussion)
• NOAA U.S. Winter Outlook news release
• NOAA/NIDIS Southern California Sector-Specific Drought Outlook Pilot
• NOAA Physical Sciences Laboratory
• NOAA climate.gov
• Zhang et al., Journal of Climate (2018)
• National Weather Service Los Angeles/Oxnard and San Diego
• USDA National Agricultural Statistics Service (Honey Bee Colonies)
• Auburn University / U.S. Beekeeping Survey
• Penn State Extension
• Cornell University (Seeley, Apidologie 2017; media tip sheet)
• UC Statewide IPM Program (Pest Notes Pub. 74159)
• UC ANR Beekeeping in San Diego County
• UC ANR Bug Squad blog
• UC Davis Laidlaw Honey Bee Research Facility
• UC ANR Publication 8068
• UC Riverside News
• Los Angeles County Agricultural Commissioner/Weights and Measures
• County of San Diego Department of Agriculture, Weights and Measures
• California Department of Public Health
• UF/IFAS Extension
• farmdoc daily, University of Illinois