Is mold in a hive a problem?
Some mold in a hive is common and often not serious. Honey bee colonies live in a warm, humid enclosed space, and mold can appear on pollen stores, on dead bees, on empty comb and on frames the bees are not covering. A strong, growing colony will often clean it up on its own.
Mold becomes more worrying when it is widespread, when the colony is weak, or when it is combined with signs of wetness such as condensation dripping on the cluster in winter. In those cases, it is worth looking at moisture management and colony health.
Why mold forms
- Dampness. Rain getting in, poor drainage or a hive in a constantly wet place.
- Condensation. Warm air from the cluster hitting cold surfaces, especially in winter.
- Poor ventilation. Air that cannot move through the hive.
- Unoccupied comb. Stored pollen and comb that the bees are not tending, particularly in a small colony with too much space.
- Wet stored equipment. Supers and frames stored damp or sealed in containers.
Moisture control
- Site the hive well. Choose a spot with good air flow and some sun, and keep the hive off damp ground.
- Make sure the roof is weatherproof. Check for leaks.
- Ventilate. Adequate ventilation, such as an upper entrance or ventilated cover, helps moisture escape. Approaches vary by climate, so look at what experienced local beekeepers do.
- Manage winter condensation. Some beekeepers use a quilt box or similar so condensation does not drip on the bees (see how colonies stay warm in winter).
- Match space to colony size. Reduce boxes the bees cannot cover, and consider an entrance reducer so the colony can manage its environment. Be careful that reducing the entrance does not limit airflow in damp conditions.
Cleaning moldy frames and stored equipment
- For a living colony, one option is to place moldy frames in the hive and let the bees clean them, giving them a strong enough population to do so.
- Scrape off heavy growth from woodenware, and let equipment dry in sun and fresh air.
- Some beekeepers use a diluted bleach solution on hive bodies as a last resort. Rinse and dry thoroughly, and do not use bleach on frames or comb the bees will use.
- Store spare frames in a dry, ventilated space.
- Discard comb that is badly rotted or heavily contaminated.
When mold is a sign of something else
Mold can accompany a dead or declining colony, wet conditions that have stressed the bees, or old stored pollen. It is not the same as disease in the brood. If you see sunken or perforated cappings, discolored larvae or patchy brood, that is a different issue and you should contact a local bee inspector. See also white worms in a bee hive if you find larvae in damaged comb.
Staying safe when handling
Mold spores can irritate some people’s airways, especially if you have allergies or asthma. Consider wearing a mask when handling heavily moldy equipment, and work outdoors or in good ventilation. If you have symptoms after handling it, talk with a doctor.
FAQ
Does mold kill bees? Not usually by itself. It can be one of several signs that a colony is stressed or in damp conditions.
Can I use moldy honey? Honey with obvious mold or fermentation is better discarded, because quality and safety cannot be assured.
For other things that threaten colonies, see our overview of insects and animals that kill honey bees.