As Beekeepers Face Record Colony Losses, 2026 Swarm Season Arrives 17 Days Early
Analysis of weather patterns and swarm reports across 56 monitored regions shows the earliest in Swarmed's four years of tracking, driven primarily by an unusually warm winter and spring on the West Coast and in the Mountain West.
17 days
Earlier than 2025 nationally
Based on GDD threshold analysis across 56 regions
84%
Of North America currently in active swarm season
71 regions at Peak Activity, 120 High, 429 Moderate
4,032
Swarm reports already submitted in 2026
6,056 active beekeepers alerted
Published by beeswarmed.org · May 2026 · Updated daily · Based on 17,000+ georeferenced swarm reports
“The 2024-25 Apiary Inspectors of America survey showed beekeepers lost 55.6% of their colonies over winter, the highest loss rate since the annual survey began in 2010. So this spring beekeepers are extremely eager to catch swarms to replenish their hives with strong local bees.”
Swarm Season
1 Seeley, T.D. (2010). Honeybee Democracy. Princeton University Press.
Where Spring Is Arriving Earliest
Most ahead of 2025
- 178 days earlier
San Francisco County
CA
- 263 days earlier
San Mateo County
CA
- 363 days earlier
Larimer County
CO
- 453 days earlier
Marin County
CA
- 548 days earlier
Nevada County
CA
Closest to 2025 pace
- 16 days behind
Broward County
FL
- 25 days behind
Pasco County
FL
- 34 days behind
Miami-Dade County
FL
- 43 days behind
Manatee County
FL
- 52 days behind
Florida (state)
FL
Based on GDD threshold-crossing dates using region-specific learned thresholds. Only regions with 10 or more matched swarm-weather observations included. 56 regions met this standard.
of North America is currently in active swarm season
- A region is considered active when its daily swarm likelihood score exceeds 45 out of 100
- Likelihood scores combine weather conditions, accumulated Growing Degree Days, and habitat factors
- Scores are recalculated each morning using weather data from Open-Meteo across all monitored regions
How to read this map
Swarm Season Progress by State
“By running a national swarm reporting network we're able to get more swarms to beekeepers, but we're also building up data on seasonal patterns that we couldn't see before, and share those with beekeepers and researchers.”
What Swarmed does
Methodology & Data Sources
The findings on this page are derived from two independent analytical methods that both point to the same conclusion. Weather-based analysis compares the date when accumulated Growing Degree Days crossed each region's learned swarming threshold in 2025 versus 2026. Report-based analysis compares the shape of each year's swarm report curve, normalized as a percentage of annual total to control for Swarmed's growing network. Both methods produce a result of approximately 17 days ahead for 2026.
The dataset
The predictions shown here draw on a database of over 17,000 georeferenced honey bee swarm reports collected through beeswarmed.org across North America and Australia. Each record carries a GPS coordinate, date, and outcome. This is believed to be the largest dataset of its kind used for predictive modeling.
The weather model
Swarmed scores daily weather conditions for each monitored region using five variables: accumulated Growing Degree Days (GDD) since January 1st — a standard measure of accumulated warmth above 10°C used in agricultural forecasting to track biological readiness in insects and plants — maximum daily temperature, peak solar radiation, the number of warm days in the preceding week, and whether rain occurred. GDD thresholds, the accumulated warmth at which swarms typically begin appearing, are learned separately for each region from its local historical record, rather than applying a universal fixed date.
Research basis
Henneken, Helm & Menzel (2012) established temperature and rainfall as the primary meteorological drivers of swarm emergence using a crowdsourced dataset of 1,335 swarm events in Germany (Environmental Entomology, 41(6), 1462–1465).
Regional variation in phenological response
Recent experimental research provides context for the regional variation observed in Swarmed's 2026 data. Ganuza et al. (2026) exposed 14,921 cavity-nesting bees and wasps from 161 sites across a climate gradient in southern Germany to experimental post-winter temperature treatments simulating current and projected future conditions. Their findings confirm that bee emergence timing is highly plastic to post-winter temperatures, with insects emerging earlier in warmer treatments, but that this response is consistently modulated by the long-term climate of each population's origin. Spring-emerging species from warmer climates advanced their emergence more strongly under warming conditions than cool-adapted populations from cooler regions, a pattern consistent with local genetic adaptation. This helps explain why Swarmed's analysis shows dramatically earlier seasons in California and Colorado while Florida and the Gulf Coast track close to historical norms: populations in these contrasting climates appear to respond differently to the same warming signal. Ganuza et al. also find that cool-adapted spring-emerging species face the greatest fitness costs under warming, losing up to 34% of body mass at emergence under warmer post-winter conditions, raising questions about whether earlier seasons in cooler regions reflect equivalent colony health to earlier seasons in historically warm regions. Note that this study examined solitary bees and wasps rather than honey bees specifically; the phenological mechanisms are analogous but not directly transferable to honey bee swarming biology.
Surge events
When a colony has been confined by rain or cold for three or more consecutive days, swarming pressure accumulates. The first suitable flying day after such a period produces a spike in swarm activity. Swarmed detects these events automatically and sends alerts to beekeepers in affected regions. Surge conditions require peak solar radiation above 400 W/m², maximum temperature above 20°C, and no rain on the release day.
Habitat factors
Two locations with identical weather can have different swarm activity based on their environment. Each location is also scored on historical swarm density at that site and proximity to active registered beehives within 3km. A third factor, mature tree canopy cover derived from the Meta/WRI Global Canopy Height Model (Tolan et al., 2024), identifies areas with trees structurally capable of hosting honey bee nesting cavities, adding signal in forested areas underrepresented in observational data.
Trap placement
Swarm trap recommendations follow the nest site preferences established by Thomas Seeley's controlled experiments at Cornell and Appledore Island (summarised in Honeybee Democracy, Princeton University Press, 2010): 40-litre cavity volume, entrances of 12.5–75 cm², height above 3 metres, southeast-facing orientation.
Key references
- Henneken, R., Helm, S., & Menzel, A. (2012). Meteorological influences on swarm emergence in honey bees. Environmental Entomology, 41(6), 1462–1465.
- Bila Dubaić et al. (2021). Unprecedented density and persistence of feral honey bees in urban Belgrade. Insects, 12(12), 1127.
- Ganuza, C., Redlich, S., Holzschuh, A., Hovestadt, T., Mitesser, O., Göllner, S., Klein, A., Summ, T., & Steffan-Dewenter, I. (2026). Climatic origin and plasticity shape emergence timing and fitness in bees and wasps under experimental climate regimes. Functional Ecology. https://doi.org/10.1111/1365-2435.70309
- Rutschmann et al. (2025). Swarming rate and timing of unmanaged honeybee colonies in a forest environment. Insectes Sociaux.
- Seeley, T.D. (2010). Honeybee Democracy. Princeton University Press.
- Tolan et al. (2024). Very high resolution canopy height maps from RGB imagery. Remote Sensing of Environment, 300, 113888.
Data limitations
The 17-day seasonal advance reflects regions with sufficient matched swarm and weather observations across both 2025 and 2026. Estimates are most reliable in areas with consistent spring activity and may refine as additional reports come in throughout the season.