Wax moth caterpillars construct silken tunnels in beeswax comb, incorporating their fecal matter. Unchallenged by adult workers, caterpillars can quickly destroy beeswax comb. Moth pupae attach their cocoons securely to wooden hive parts, in boat-shaped indentations. The moth adults are undistinguished brown moths with a prominent snout; lesser wax moths have a yellowish head.
Both greater (Galleria mellonella; sometimes called honeycomb moth) and lesser (Achroia grisella) wax moths are night-flying moths considered pests of beeswax comb. They have a worldwide distribution, with the lesser wax moth being more common in warmer climates. Wax moth is a misnomer as neither greater nor lesser wax moth can survive on beeswax alone.
Wax moth caterpillars are a comb scavenger that can quickly completely destroy beeswax comb. Wax moths do not kill active bee colonies, though they are often believed to do so by beekeepers.
Adult moths lay eggs in cracks and crevices to avoid removal by worker bees, or they may lay eggs in unprotected stored comb. Moth caterpillars construct silken tunnels in beeswax comb, incorporating their fecal matter. The caterpillars feed on cast larval skins, pollen, and honey. They can quickly reduce drawn brood comb to webbing and debris.
They do not commonly tunnel in honey storage combs, but they can render comb honey unattractive if they tunnel beneath the cappings. As a scavenger, they can quickly reduce the beehive’s most valuable asset, drawn beeswax combs, to total waste under the right temperature and humidity conditions.
A condition called galleriasis occurs when normal worker and drone bees are trapped inside their cell and are unable to emerge because they are webbed in by the silk produced by the wax moth. When adult bees uncap adjacent cells (apparently looking for the caterpillar so they can remove it) a condition termed bald brood appears. Uncapping of several adjacent cells is normal.
Mature greater wax moth caterpillars exceed an inch in length while lesser wax moth caterpillars are only about half that size when mature.
Moth pupae attach their cocooncocoon:
very thin, protective silk envelope which an insect larva or pre-pupa forms about itself by spinning the envelope while inside the cell, to change to the pupal stage
securely to wooden hive parts, in boat-shaped indentations. The moth adults are undistinguished brown moths with a prominent snout; lesser wax moths have a yellowish head.
Wax moths don’t kill a colony. The usual scenario is that adult wax moth females find dying or weakened colonies—colonies whose population is unable to effectively protect its comb—in which to lay their eggs. The weakened colony does not remove the caterpillars as they normally would in strong, healthy colonies, and the caterpillars grow quickly, causing noticeable damage.
Stored drawn brood comb, unless protected in storage, can quickly be reduced to debris. Honey storage comb offers no food for wax moths, so it does not need to be protected in storage. Frames from dead or dying colonies that have been used to rear brood or which contain stored pollen are especially attractive to the caterpillars, since the protein the caterpillars need to grow is available.
There are numerous controls for wax moths. It is especially important to be vigilant in wax moth control in regions where winter temperatures are warmer and/or when empty combs are stored in a heated facility.
Strong colonies, capable of patrolling their entire comb surfaces, will keep wax moths in check. Sudden adult depopulation, a pesticide kill, winter deadouts, or other situations where the adult population is diminished, may lead to wax moth caterpillar damage of the unprotected comb.
Stored brood comb can be protected with the pesticide paradichlorobenzene or PDB. It should not be used in combs containing honey, and it is absorbed into beeswax. Stored combs can be fumigated with one of several chemicals. Most require a special pesticide license certification to use, and special precautions should be taken when using.
On a smaller scale, the combs can be placed into a freezer for 24 or more hours and then wrapped in heavy duty plastic bagging to prevent reinfestation. Spraying with the biological control agent Bacillus thuringiensis (BT) protects comb for a period of time.
For honey-extracted frames, open air circulation, sunlight, and protection from moisture usually offer sufficient protection from wax moth infestation.
Wax moth caterpillars can be confused with fly maggots, other scavenger moths, and even beetle larvae such as the small hive beetle.
BeeAware. n.d. Wax moth. BeeAware. Accessed 2023. https://beeaware.org.au/archive-pest/wax-moth-18/#ad-image-0
Hood WM. 2010. Wax Moth IPM. Clemson Cooperative Extension. Accessed 2023. https://www.clemson.edu/extension/beekeepers/fact-sheets-publications/wax-moth-ipm-publication.html
Snyder R. 2020. Detecting Wax Moth Larvae in Frames of Sealed Brood. BeeInformed. Accessed 2023. https://beeinformed.org/2021/07/02/detecting-wax-moth-larvae-in-frames-of-sealed-brood/
Jack C and Ellis J. 2021. Wax Moth Control. University of Florida/IFAS Extension. Accessed 2023. https://edis.ifas.ufl.edu/publication/AA141
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