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.

learning from natural honey bee nests

It’s winter and I’m thinking about my bees in these recent cool temperatures; my curiosity turned to Google Scholar and searching for the beekeeper and engineer - Derek Mitchell. Here I found Derek’s 2024 paper in the Journal of Thermal Biology - Are man-made hives valid thermal surrogates for natural honey bee nests.  This is a highly technical read with an exotic mix of scientific units, but I found take-home nuggets useful to my hobby beekeeping. My goal is not to keep bees in a tree, but to modify my wintering of bees in a thin-walled wood box by learning what bees have, on their own, achieved living in tree cavities.

	Man-made hive	Tree nest
Top ventilation	Beekeeper’s  choice	None
Wall properties	Thin low R-value	Thick high R-value
Comb to wall surface	Continuous bee space separation	Comb attached to the wall with a few small gaps
Comb to roof surface	Continuous bee space separation	Comb maximally attached to tree cavity roof
Comb to bottom surface	Continuous bee space separation made more complex with multiple boxes	One continuous separation
Vertical comb length	Single frame height whether using one or multiple boxes	Continuous

Made with HTML Tables

Using 16 variables adjusted to experimental observation, Derek used computational fluid dynamics (CFD) modeling and compared the convective air flow and metabolic impact to bees in a standard British National Hive (one box of 35 Liters) versus a synthetic tree nest (45 liters).

Derek writes, “bee space above combs increases heat loss by up to ∼70%; hives, compared to tree nests, require at least 150% the density of honey bees to arrest convection across the brood area.”

Derek recommends blocking the bee space above the combs in a man-made hive, which I interpreted as adding a clear plastic sheet resting directly on the top bar frame. I have a box of letter-sized plastic sheets designed for overhead projector presentations - it seems perfect for the task. Stay tuned for how this works out for me as I am over-wintering two hives with a different number of boxes. One hive has two medium boxes, and the other hive has one deep box. I spliced sheets together with tape and trimmed the extended sheet to fit inside my eight-frame box. Each hive received one trimmed plastic sheet beneath its inner cover resting directly on the top bar frame. No doubt the bees will glue the plastic to the top bar frame and this will require some vigorous spring cleanup effort. 🤣

Perhaps you want to give this small modification a try and use different materials (e.g., wood, thick acrylic, or coroplast).

Broodminder - thermoregulation

 

Not inexpensive, but I purchased the most affordable BroodMinder sensor which measures the internal hive temperature. The sensor is a thin profile temperature data logger that rests on the top bar and syncs with my iPhone (then uploads to the cloud) where data is graphed and accessible on my iPhone or web browser.

The dashed red line is local weather data.   I'm naturally skeptical about weather data.   When I placed the broodminder in hives without bees, I found that temperature data tracked the weather data accurately.  

Hourly internal temperature data values from the sensor created the solid cranberry-colored line. Ideally the solid line tracks within the gray band (92°F - 98°F) and represents a queen-right hive.  There are many reasons why the solid line is drawn below the gray band, but I had no information as to why the temperature had climbed above the gray band to 105°F.  I'm puzzled and reached out to BroodMinder Support and Theresa Martin (author of Dead Bees Don't Make Honey) for assistance in shaping a theory.

I checked the sync with the iPhone which recorded the coin battery strength.  Nothing suspicious there, the battery was 97% of full strength.   

During the inspection of the counting board and an internal hive inspection, I discovered that the small hive beetles had compromised the honey.  The 105°F was likely created by the fermentation of honey.   I found the BroodMinder sensor and temperature graphs very helpful, internal temperature is one of many ways to monitor hive health.

Google Alerts

After a few missteps, I shaped my internet news query about swarms - my favorite aspect of beekeeping.  For the past few months I received daily emails from Google Alerts and I'm ready to share how the news media covers the topic of swarms.  I was not surprised to see the media crafted eyeball attracting internet headlines (clickbait). 

Here are 7 different internet headlines about the same bee event.  The beekeeper never appears in the headline so it's hard to describe the story as balanced.

3 workers stung by swarm of bees while trimming trees in New Jersey - FOX 5 New York

Police: 3 people hospitalized as bee swarm takes over Paramus neighborhood News 12 - New Jersey

Neighbors told to stay home after swarm of angry bees injures 3 tree trimmers, cops say
- NJ.com

Bee swarm injures workers in Paramus as police urge residents to stay inside -
northjersey.com

Cops in NJ warn of 'large swarm' after bees attack 3 workers - Audacy

Angry Bees Attack Three Tree Trimmers In Paramus: 'Cover Your Face!' (Update)
- Daily Voice

Bees Sting Employees In Bergen County Town, Sending 1 To Hospital | Wyckoff, NJ Patch
Paramus police closed Howland Avenue for a time and dispatched a beekeeper to the scene, Chief Robert Giudetti said. "The Bee Keeper arrived and accessed the situation determining if the bees are left alone they will return to the nest in the trunk of the tree ... The bees returned to the hive and the scene was cleared."

Some of the news was sad

75-year-old grandfather killed by swarm of bees while working on Texas ranch - New York Post
75-year-old Bryce Smith was clearing some trees on his property in Bedias. He was using the bulldozer and incidentally took down a bee hive while clearing the trees.

Where is the line between exploitation of the public's fear versus suggesting caution about bees?  Do semantics matter to our neighbors, or is it just me?  I cringe when people write hive when they mean nest, or write swarm when they mean guard bees.  I'm shocked by these dramatic internet news headlines, but still interested in exploring Google Alerts.

water foraging during June 2024 heatwave

In Atlanta, June 2024 was both hot and dry.  The daily temperatures were warmer than normal, touching the record high for a few days.  We accumulated 1.74 inches (4.4 cm) of rain compared to a normal June rainfall of 4.54 inches (11.5 cm).  

I rolled out the garden hose and watered daily.  The bees responded by drinking from the birdbath and packing around the edge of the ant moat that hangs above the hummingbird feeder.  

Next, I set out decorative bee-watering items with a dash of kosher salt.  How much salt is enough?  Follow this link to Salt preferences of honey bee water foragers and read that minimal salt is required to attract bees.  The unrelenting heat and the bees' keen memory of their new water source required that I top up the water several times a day.  I added a large chicken waterer 9/10 gal (3.3 liter) with a dash of kosher salt that kept up with the bees and evaporation at the waterer.  In my opinion, the key to attracting water foragers is to provide a permanent and dependable location for water.

NOAA's headline, June marked by record-setting U.S. heat waves, severe weather, highlighted tornados and flash flooding in Florida.   In Atlanta, the June 2024 experience was hot and dry.

Honey Bee Swarm Seasonality

Using David Marshall's (MABA’s swarm commander) 2022-2023 Atlanta swarm records I created a histogram graph with eight bins. The raw data has many of days with no swarms and combining two years in a simple graph does not completely patch days with no swarms days or sufficiently smooth the data. The histogram peaks on March 28 ± 10.5 days, and then there is a long tail into the summer months. 

I discovered a paper, Seasonal Cycle of Swarming in Honeybees, that combined six years of Ithaca, NY swarm emergence dates - I digitized the paper’s Figure 1A.  I created a histogram plot with nine bins. Figure 1A and the resulting histogram graph show a bimodal seasonal pattern – peaking on June 9 ± 7.5 days with a smaller peak in the summer months. 

 

 

I exchanged emails with one of the authors, Thomas Seeley, and shared how spring frost and fall frost climate data might reconcile these Atlanta and Ithaca swarm peaks. 

• The Ithaca x-axis contains fewer days than the Atlanta y-axis and is consistent with Ithaca's shorter growing season.
• In Atlanta and Ithaca, the peak swarm (orange circle) appeared before the local last spring frost.

I’ll leave it to the readers why honey bees in Atlanta don’t have a smaller summer peak like Ithaca – I don’t know. Having a pattern bias has sometimes served me well in making quick decisions, detecting missing data, or spotting corrupted data - what the typical swarm season pattern should look like is still up for grabs!

 

Swarm Trap - May 5th 2024

Swarm summary: It was an unusual swarm trap season.🤣 My neighbors helped me see a swarm select a sycamore tree cavity, and 43 days later this bee nest swarms and selected my swarm trap 7 houses away. Flight vigor at the bee nest has since increased - the bee nest is a gift that keeps giving!

 

I was hoping for something else! 

• 9th March - I installed 4 swarm traps in my neighborhood
• active scouting began at two 40-liter swarm traps hanging from crepe myrtle limbs. Each swarm trap contained:
• 5x deep frames with plastic starter strips
• UV-reactive blue swarm trap entrance
• synthetically produced Nasonov pheromone
• 23rd March in the early afternoon - my traps are passed over as the bees selected a cavity in the sycamore tree trunk using a cut-off limb entrance and active scouting of swarm traps subsided
  
• 29th April - sycamore bee nest entrance was obscured by a huge bee beard - see the 2nd photo.
  

In a roundabout way, the moment I've been waiting for!   

• active scouting restarted at the two 40-liter swarm traps
• 5th May at 5:30PM - bees selected my backyard 40-liter swarm trap and the sycamore bee nest entrance is no longer obscured by a huge bee beard - a flight journey of 290 feet (88 meters) - see the 1st photo.
  
• over the next 6 days after dark, I moved the occupied swarm trap in 5 steps towards my empty backyard hive stand.  The after-dark move was made easier by leveling the next location during daylight hours.
  
• 13th May - I transferred 5 deep swarm trap frames to 8-frame equipment and moved the swarm lure to the 8-frame landing board. No smoking or brushing of bees was required. - see the 5th photo.