Mold seems to be the topic of the week, but that is not surprising. This is the time of year when you open a hive that overwintered with little interference from you. What you find there are not gleaming combs of honey and pollen, but empty cells rimmed with white, green, blue, or yellow mold. At least it looks like mold and smells like mold. And you are right—it is mold.
Beginning beekeepers often respond by separating mold and bees as quickly as possible, treating everything with bleach, or kicking themselves for being incompetent. If all the bees are dead, mold is often fingered as the cause, as in “Mold grew everywhere in my hive and killed my bees!”
Mold in hives is natural
But wait; let’s back up. Molds (or moulds, which seem more sinister) are tiny fungi that live on plant and animal material. They thrive in humid conditions and reproduce by forming spores—great clouds of spores. These light-as-air particles are everywhere, just waiting for the right conditions so they can sprout.
Bee hives provide the perfect place for mold growth, supplying all the things molds like best: debris from plants and animals, a moist environment, and darkness. Millions of spores are waiting in the crannies and crevices of the hive with napkins tucked under their chins, knives and forks at the ready. They know the feast is coming.
Larger colonies have less mold
An active colony of bees has no problem keeping mold growth at bay. The bees clean and polish brood cells, remove dead bees, rotate stores of pollen, and remove invaders. But during the winter, the colony energy is spent in a cluster. The main interest is survival—eating and keeping warm. Housekeeping is put on hold.
As the winter progresses, the cluster becomes smaller and the bees move up through the boxes, eating their way through the honey stores and leaving empty, unattended combs behind. The mold gleefully takes over.
To make matters worse, a layer of debris accumulates on the bottom board or screen—vast helpings of dead bees, mites, bits and pieces of comb, feces, drips of honey. The mold is beside itself with happiness and joy. It reproduces like crazy. A mold spore in a winter hive thinks it died and went to heaven.
A growing colony will remove mold from your hive
But as spring approaches and the colony begins to expand, the now active bees begin regular housekeeping duties. The dead are hauled out, the cells are polished, and all that mold disappears in a flash. The bees know what to do.
On the other hand, if your colony died, it died of something else and then the mold took over. Excessive mold is the result of colony death, not the cause of it. I’ve seen beekeepers discard everything in sight just because of mold, which is silly and wasteful. Mold is a natural part of the entire beekeeping process.
Don’t apply your mold standards to bee hives
The problem with mold is that we, as pampered humans, apply our own standards to the bee hive. In our own lives, we go to extremes, even buying food laced with calcium propionate, sodium benzoate, and potassium sorbate so little furries don’t start on our dinner before we do.
These chemicals are usually acidic substances that delay mold growth. Most mold doesn’t do well in acidic conditions, which is why honey (very acidic) is slow to grow mold. It also explains why a little vinegar or lemon juice in sugar syrup can delay mold for a while.
Use bleach as a last resort
If you can’t stand the mold and simply must do something with those combs before you give them back to the bees, put them in a warm and dry environment for a few days with plenty of space between them. This will stop the active growth phase. Some people like to spray with bleach. Bleach is okay but if the combs don’t dry out quickly, the mold will just grow back. Sunlight discourages mold growth as well, but be careful not to melt your combs.
I recommend just leaving moldy frames with the bees. If you check those frames after the colony has a chance to work on them, you won’t be able to tell them apart from any other frames. Applying your own standards of housekeeping to bees will make you crazy and give your bees the last laugh.
Honey Bee Suite