Burr Comb, Bridge Comb – Managing Unwanted Combs
“Burr comb” is when bees build wax comb between the top bars and hive lid. “Bridge” comb is when its built between two frames hence “bridging” the two together. I classify cross comb as a type of bridge comb and likewise with “brace” comb… Although it could be considered structurally necessary in a natural beehive. Different regions have different names for these constructions, and I will be referring to the collective as “burr comb”.
To manage excess comb between the top bars and hive lid, place an “inner cover” – a slim piece of corflute (“fluteboard”) or sturdy plastic that’ll cover the majority of the top bars, leaving room for the bees to crawl through. For bridge comb between frames, evaluate your hive setup: are you leaving too much room and exceeding the bee space of 6-9 millimeters?
Why do bees make burr comb, and should beekeepers remove it? What happens if the comb is undisturbed for months? Read on and find out. Or don’t. That’s fine too.
Managing Burr Comb
Honey bees perceive that their hive has “too much space” and begin building comb to bridge the gaps. You can manage this by providing them with the illusion of sufficient space. For the bridging comb between frames, add another frame (e.g. if you have eight frames in a ten frame hive, add one more), and/or evenly space the current frames apart. I don’t like using ten frames in a ten frame hive because of how crowded the hive box becomes, however using the maximum amount of frames per box will resolve your bee space issues.
For excess comb between the hive lid and top bars, provide an inner cover. Some suggestions:
Use an “inner board”, the surface which an in-hive feeder sits when providing supplemental feeding.
Add a quilt filled with wood chips to improve insulation, and manage excess moisture.
This is what Warre hive beekeepers place between their top bars and hive lid.
Most simple: on the top bars, place a piece of corflute plastic, or any non-toxic thin sheet that won’t be chewed away by the bees.
The key is to allow bees access onto the lid surface for pest patrol/ventilation without leaving excessive space that causes them to build comb and bridge gaps.
Excess Wax and Pests
More wax, more pests. More pests in spaces not regularly patrolled by worker bees combined with a weak colony means you better prepare for trouble, and make it double. Wax moths lay eggs in beeswax, and their larvae tunnel through the comb, eating wax, pollen and cell cappings. Likewise, small hive beetles hide in the irregular spaces created by burr comb, feeding on pollen, honey, and brood. Their larvae tunnel through wax, consuming everything and fermenting the nectar with their faeces, leading to a slimeout. Lovely.
Does Extra Wax Endanger the Queen?
What about Her Majesty? How does the excess comb impact her? The short answer is that burr comb has no direct impact on queen health. The indirect impacts come from the increased difficulties in hive management. How many times have you had to pry frames apart with your hive tool? Imagine if the queen was on the surface of those frame and was jolted against the neighbouring frame – given her larger size, she could end up injured, or even squashed.
I wouldn’t put “queen health” high on my list of reasons to remove burr comb, so long as you’re confident in your beekeeping approach.
Biology of Burr Comb
From a biological perspective, burr comb is the colony’s attempt to make the most of available space within the hive. Great for bee, not for me. Inspections and frame removals become much more complicated, starting with opening the hive lid1. A paper by Camazine likens comb to an extension of honey bee behaviour (Camazine, 1991). The bees construct three areas: the central brood frame, the surrounding layer of pollen and the peripheral honey stores. If the hive identifies a gap between the top bars and the lid, they assign the space into the “peripheral” category, and begin storing honey… Well, that’s what mine do.
Burr Comb as an Example of Decentralised Control
No single bee decides “I’m going to build here!”. The entire colony responds to cues from their environment (the hive components), and feedback loops. Every step taken by a worker relays information. When the number of drone comb reaches a threshold, a negative feedback loop takes place and the workers stop building more drone comb (Pratt 1998). The queen has no say in this, for she is led by the workers to empty cells, and after feeling for the cell dimensions with her forelegs (~5.2 mm wall to wall for workers & ~6.4 mm for drones ) she lays a fertilized or unfertilized egg respectively.
Burr comb is the bees’ adaptive response to their immediate hive habitat. The comb and its structure influences behaviours like brood rearing or foraging. It is a signal of crowding, space availability, and whether they should maintain or expand certain areas, including that space between the lid and top bars.
Empty, Not Full Comb Provides the Signal
Why does the presence of empty and not “filled” comb determines what should be constructed next? After all, who knows when that cell will be filled? Consider that drone rearing takes place over 2-3 months, the peak of spring & summer, whilst the activity of comb building happens year-round in temperate climates. If a colony was to depend on the contents of the comb to regulate construction, then they will overbuild in anticipation of the season ahead, and likely waste hive resources in doing so. We cannot predict the weather and bees are no exception, so the number of empty combs set the “limit” for the amount of construction.
Burr Comb and Drone Brood
The typical Langstroth hive has foundation frames sized for worker brood. It doesn’t bother bees, after all, workers are the most important resource, and pollen/honey are easily stored in worker-sized comb. What about drone comb? When bees rear drone brood on the foundation, the comb protrudes from the worker cells as it is reshaped to meet the drone larvae’s measurements.
Enter burr comb. Since it’s built in irregular or unstructured spaces, the frame’s cell-size constraints do not impact the bees. This flexibility enables them to construct larger cells for rearing drones, meeting the colony’s drone production quota in preparation for swarming.
Zhang and colleagues showed that in foundation containing larger cell size, the size of the emergent drone increased in relation to the cell size (Zhang et al., 2024). Cell sizes from 5 mm to 7 mm were tested, and as cell size increased, so did drone body size2. These larger male bees would have an advantage over smaller drones in terms of mating and chasing virgin queens (Couvillon et al., 2010). I interpreted Zhang’s results as suggesting that burr comb could be the bees’ response to the size constraints of the worker-sized foundation cells, giving them the freedom to sculpt their own wax comb.
Case for Removing Burr Comb: Varroa Control
Varroa mites prefer larger-sized (and thus drone) comb over worker comb for reproduction (Many sources in the literature, e.g. Martin & Kryger, 2002 or Oddie et al., 2019). A more controversial topic is that cell size for Varroa control doesn’t matter. In the case of the aforementioned paper from Martin & Kryger, they found that size matters for the Varroa males, who are laid first near the wax cappings. When there is less cell space to move, it is harder for the male to access the feeding site left behind by their mother foundress towards the bottom of the cell.
The lack of movement means the male mite starves, and since one male is laid per cell, the subsequent females emerge unfertilized. From this result, we see that excess comb containing drones is a Varroa breeding ground. So unless you want extra drones from your colony for queen rearing, remove that drone-bearing burr comb to help keep Varroa levels under control – after all, drone trapping is a valid integrated pest management method for mite control .
Making use of Excess Comb
You don’t have to listen to me and remove excess comb. Sometimes, I don’t even listen to myself. Burr comb is a rewarding nuisance, for I harvest the excess and eat it as whole honeycomb (after removing the bees, of course.. unless it’s drone brood). If there’s excess comb in the brood nest, I scrape it with my hive tool and place it in a bucket for processing. Inedible, unwanted comb is great for rendering and turning into wax blocks – mine tends to have a brighter yellow colour, and is less impacted by hive debris.
So if you don’t want to do anything about burr comb, don’t. Harvest the honey-filled comb covering the lid, and melt the ones found between frames, simple as.
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Footnotes
- I used to keep a “Pigeon lid” one of my hives until one day it was near impossible to open due to the excessive burr comb buildup. Pigeon lids are designed so that lid edges jut out from the hive box, rather than sitting on top as in the standard telescopic lid. It requires a vertical rather than horizontal force to dislodge. Not easy to do when the hive is sealed shut – every hit of the hive tool moved the entire hive, and the ladies weren’t happy with me that day. ↩︎
- Drones reared in wall-to-wall cell sizes of 7 mm were larger then those reared in their natural ~6.5 mm cells. This does not mean that beekeepers should start using large plastic foundation for drone rearing, rather they should consider the implications of a larger cell size: more Varroa mites developing per cell, more difficulty in maintaining individual cell temperature and perhaps increased sensitivity to physical stressors – an accidental shockwave following the frame’s fall onto the ground (since there is extra room for the pupa to move in). ↩︎