15 Minutes of Bee Flight

  

Growing Degree Days

According to Growing Degree Days (GDD), accumulated heat levels in Atlanta are already brushing up against historic highs. You can see it everywhere: trees leafing out, stone fruit bursting into bloom, and pollinators getting a head start on their busiest season. In my neighborhood, bees are making the rounds—crabapple, ornamental cherry, holly, even the occasional dandelion are all part of the early buffet.  Dave Marshall, our swarm commander, received our first swarm call on March 3rd.

15 Minutes of Bee Flight

Back in 2012, NASA coined the unforgettable phrase “Seven Minutes of Terror” to describe the landing of the Curiosity Rover on Mars. It captured a brief, intense, high-stakes moment. I found myself thinking about that on Sunday, March 15, when my own backyard delivered a headline-worthy event: “15 Minutes of Bee Flight.”  At 11 a.m., under warm sun and blue skies, my five-frame hive swarmed.

If you’ve never seen a swarm in motion, it’s easy to miss—or misunderstand. From a distance, it’s just a buzzing cloud. Are they leaving? Arriving? It’s impossible to tell. But when you focus—really focus—on the landing board, the story sharpens. In my case, it looked like a moving walkway, a steady stream of bees flowing outward. The old queen and roughly half of the workers and honey are gone!     

I managed to capture it on my iPhone, a small victory considering how fleeting these moments are. Within minutes, the airborne cloud settled high in a Leyland Cypress tree—far too high to reach. So I did what any beekeeper would do in that situation: grabbed binoculars, stared upward, and chatted with a neighbor about the spectacle.

By the next morning, the story had changed.

I was out at dawn, scanning for the swarm. The good news: they had moved on. The bad news: the temperature had dropped hard overnight. On the neighbor’s driveway lay the aftermath—hundreds upon hundreds of dead bees, casualties of the cold. Maybe a thousand in total. Not nearly enough to represent the full swarm, but enough to tell a sobering story.

These were the bees that formed the outer shell, sacrificing themselves to give the colony a chance to survive. It’s a stark reminder of how collective survival works in a hive—individual loss in service of the whole. My neighbors, wonderfully kind about the whole thing, even asked if I wanted to hold a proper ceremony for the fallen. 

In Summary

And that’s the thing about beekeeping, especially in a year like this. 

What begins as a perfectly timed departure—a warm, sunny launch into the promise of spring—can collide almost immediately with the unpredictability of nature. A brilliant plan meets a sudden freeze. It’s hard not to view it through a human lens, to look for logic or fairness in it. But the bees don’t operate that way. They respond, adapt, endure—or don’t.

Climate Prediction 2026

Brood Break Observations in Two Backyard Hives

8-Frame Hive:
This colony experienced a brief brood break from October 19 to November 19, 2025, but showed no noticeable response to the January 10, 2026 cold snap. In fact, a few drones were spotted on February 8. Overall, the colony’s behavior resembles an early spring buildup more than typical winter activity.
5-Frame Hive:
In contrast, the 5-frame colony slowly responded to the January 10 cold spell with an additional brood break. It has recently begun raising internal temperatures back into the brood range of 92°F–98°F, signaling renewed brood rearing. 

Understanding the BroodMinder Graph
The 5-frame hive graph includes three temperature curves:

• Raspberry curve: Temperature at the top of the lower box
• Purple curve: Temperature at the top of the second box, just beneath the inner cover. 
• Red curve: Outdoor temperature from a third-party source

At present, the purple curve remains below brood-zone temperatures, indicating no brood in the upper box. Meanwhile, the raspberry curve has climbed back toward brood-range temperatures following the most recent brood break.

Understanding the Growing Degree Days (GDD) Graph
The smooth brown line represents the multi-decade average of Atlanta’s Growing Degree Day (GDD) accumulation. GDD measures accumulated heat units and can seem abstract at first.
The jagged green line shows the current 2026 GDD. Prior to January 10, it tracked above the brown average line, reflecting warmer-than-normal temperatures. After January 10, the flat section of the green line indicates temperatures below 50°F. At present, the 2026 GDD has returned to near-average levels. In my swarm-obsessed view, average GDD values suggest a typical start to the Atlanta swarm season.

What’s Next?
The outlook from the National Oceanic and Atmospheric Administration offers limited hope for drought relief. For Atlanta, a modest chance of warmer and drier conditions could support foraging activity.  There is always a gray area between long-term climate outlooks and short-term weekly forecasts, so patience will be essential as the 2026 bee season unfolds.
February and March are likely to bring swings between unseasonably warm spells and freezing conditions. During cold, damp, overcast days with no flight activity, it can be unsettling not knowing what’s happening inside the hive. Fortunately, BroodMinder temperature loggers continue to provide valuable insight and reassurance. Stay tuned for further updates as we follow how these colonies navigate an unpredictable winter.

Growing Degree Days and swarm collection

In Better Beekeeping, Kim Flottum described Growing Degree Days (GDD) and how this measure of heat accumulation predicts plant blooming. A growing degree day is a formula that reflects temperatures above 50°F which is the most common base temperature.

For example, red maples (Acer rubrum) begin to bloom when they reach a GDD threshold of 30–50 GDD (base 50°F). I started thinking that there was a relationship between GDD and swarms. I returned to Kim’s GDD page over several years struggling to relate GDD and collecting swarms - my favorite aspect of beekeeping.

At first glance, GDD calculator rules and heat accumulation bookkeeping results might look abstract - you are not alone.

Atlanta, GA	Atlanta, GA
First Swarm Date -	Growing Degree Days
Date from David Marshall	(GDD BASE 50 °F) data from NOAA GDD calculator
2-Mar-22	173
25-Feb-23	312
1-Mar-24	176

Explanation of the Atlanta first swarm date versus Atlanta GDD table

Thanks to MABA’s swarm commander, David Marshall, I have three years of swarm collection data and combined these three first swarm dates with NOAA’s GDD plot. GDD measured on the first swarm day shows that 2023 GDD has a surprisingly large value compared to 2022 and 2024. In the table, two of these 3 data points (2022 and 2024) are extremely similar, but I nevertheless connected all points with a straight line. Wow, a relationship between GDD and swarm collection seems within reach!

Explanation of the Accumulated GDD graph

• Smooth brown line is an average of several decades of Atlanta’s GDD calculations
• Blue line is Atlanta’s historically highest GDD calculation (2017)
• Red line is Atlanta’s historically lowest GDD calculation (1915)

Black line passes through Atlanta’s first swarm dates of 2022, 2023, and 2024. For simplicity, Atlanta’s GDD curves for these three years are not shown, but those curves lie between the blue and brown curves. I hypothesize that years with GDD curves closer to the blue curve also have their first swarm date earlier in the year - as much as eight days earlier in the Atlanta area compared to an “average” year.

Explanation of NOAA’s historical last freeze day

Georgia includes a wide range of historically average last freeze dates, which implies that your local bee club GDD curves do not match my experience in Atlanta. Please do not hesitate to share your club’s swarm collection dates with me - I promise to treat your data with respect and acknowledgment.
In summary, it’s not too early to make a plan to find your swarm traps (bait hives) in winter storage and spruce up that trap (paint, frames, and lure) before the start of the 2025 swarm season. Keep an eye on your local GDD curve. In hindsight, Atlanta’s 2023 higher-than-average GDD trend was detectable in late January.

pollen color and winter 2020-2021

Here I'm using Growing Degree Days (GDD) to compare this Atlanta winter with previous winters. I calculated GDD using a web based calculator.  As seen in the table, this winter's GDD are much smaller than last year, with the nearest similar winter GDD found in 2013-2014. 

The back yard bees currently return with bright orange pollen and infrequently return with grey pollen - click on the image to enlarge. I'm using a wiki page of pollen colors of plants in hardiness zone 5, while Atlanta is found in plant hardiness zone 7 which presents challenges when comparing:

• plant flowering dates
• matching pollen color with a limited number of trees and plants
  

Other than color, I'm not able to analyze the bright orange pollen, but it's most likely sourced from winter-flowering ornamental cherry trees blooming in the neighborhood and attracting honey bees.

Using binoculars, I see that red maple trees are not yet flowering.  With evidence from previous years, I'll guesstimate that rosemary is the source of the grey pollen.

2019 spring bloom markers

This Atlanta spring has been like no other year, nor have we ever experienced an average spring.    Yet, I want a rough guide to plan my spring beeyard tasks.   At the moment, hives are in a winter configuration with bee cozy hive wraps and bradford pear and redbud trees blooming.

On February 21st, Atlanta pollen count exceeded 1000 which coincided with a Growing Degree Days (GDD) of 90. I'll use GDD equal to 90 and compare this spring with previous years. I calculated GDD using data from the University of Georgia Automated Weather Network.  I'll also use Julian Day  which converts a MMM-DD-YYYY date format which spans 4 months (January to April) into a seamless day of year format.

In the graph notice:

• similar Day of Year values between this year and 2018
• warm 2017 outlier which reached a GDD equal to 90 on January 19

2018 spring bloom markers

I was hoping to simplify my tracking of spring bloom markers, but instead I added another marker, Growing Degree Days (GDD), which is easy to calculate using free web-based tools.  Julian Day allows me to convert MM-DD-YYYY date format which spans 3 months (February to April) into a seamless day of the year format. GDD is a major convenience, I can tap into a database of daily temperature minimum and maximum instead of recording my own observations.  Focusing on the last two graph points, the accumulated warming this year is roughly 25 days delayed compared to last year (84 versus 59).

Here I compare additional observations with GDD, 1) Acer leaf-out in my backyard and 2) first day that the pollen count exceeds 1000.  Notice how well these markers follow similar graph trends.

Here I show a free web-based tool by AgroClimate which compares this year's GDD to the previous year.  Reading from left-to-right, notice where the curves depart - last year's accumulated warming began in mid January, approximately 30 days earlier than this year.  If the daily high does not exceed 50°F, then the daily contribution to accumulated GDD is zero - the curve does not grow in height. I love this graph layout, but I can't use this tool to go back further in history. This tool can draw the average GDD (not shown), but we all know that no such thing exists in the wild - we have never experienced an average year of weather.

Here I show a free web-based tool by Weather Underground which I used to calculate GDD beyond the previous year in history.  In previous years, I kept the starting point equal to January 1, and I change the ending point in a trial and error manner to achieve a GDD value close to 296.  Why 296 - this is the GDD value where the Atlanta pollen count exceeds 1000 this year.

                     2009 2010 2011 2016 2017 2018 

                      day  day  day  day  day  day

Bradford Pear          65   79   60        56   53
Carpenter Bees         68   87   72        63   77
Acer palmatum leaf out 73   92   77        64   76
Carolina Cherry Laurel 73   97   83        57   76
Pollen Count over 1000                76   51   84
GDD=296 (base 50°F)    92  104   93   84   59   84
Here I show other values that do not appear in the graphs.