It doesn’t take long to discover that brood combs turn black as night after just one season while honey combs stay light for years. What causes this difference?
Several reasons account for the discrepancy. But in truth, a combination of factors causes brood comb to darken more quickly than honeycomb.
The cocoons that remain in the cell after the bees hatch are the major problem. The cocoons are extremely sticky and, try as they might, the bees cannot strip them from the comb. Entomologists say the darkness is caused by the feces that remains woven into the bottom of the cocoons. Although the bees clean and polish the brood cells before they are reused, much of the fecal material remains trapped within the sticky layers.
Sticky surfaces attract debris
In addition to feces, the cocoons attract loose hive debris. Items such as dirt tracked in on bee feet (many bees times six), pollen grains, and atmospheric dust get trapped.
Once the young bees emerge, the workers add a layer of propolis to the insides of these cells. The layer of propolis makes the surface smooth and clean. Also, it contains many antimicrobial agents that make for a healthy colony. But propolis is usually dark red or brown, which accounts for even more color change in the brood area.
So the combination of sticky cocoons, bee feces, debris, pollen, and layers of propolis make the brood combs darker and darker.
Brood combs turn black because of heavy use
But, you say, the inside of honey cells are brushed with propolis too. That is true, but the honey cells do not contain cocoons and they are emptied and polished seldom—usually only once a year. Brood cells, on the other hand, can be polished and reused every 21 or 22 days during the spring and summer—a huge difference.
Another difference between honeycomb and brood comb is the amount of bee activity. Once a honey cell is filled the bees move on to another. But once an egg is laid in a brood cell, the uncapped larvae is fed a thousand times a day—quite a different traffic pattern.
The buildup of cocoons and propolis in brood cells is significant. Some researchers have analyzed brood comb and found that the cells become measurably smaller as the walls become thicker. If you render your own beeswax, you know how much more debris is filtered from dark brood comb than from melted honeycomb. Clumps of this debris, appropriately called “slumgum,” clog strainers and mesh bags, and tiny bits of it darken the liquid wax.
Is dark brood comb harmful to bees?
The question always arises whether dark comb is harmful to bees. In truth, bees love dark comb and it is often used in bait hives to attract wild swarms. I’ve heard rumors about beekeepers using black comb for twenty-five years with no ill effects.
Recently, however, there is concern about pesticide build-up in old combs, as well as the accumulation of some pathogens. Many sources now recommend rotating old black comb out of the hive every four or five years, not because of its color but to protect the hive from accumulations of pesticides and pathogens.
Honey Bee Suite