Wax moths are a persistent challenge in beekeeping. The two primary species are the Greater Wax Moth (Galleria mellonella) and the Lesser Wax Moth (Achroia grisella). These pests are scavengers that target honey bee colony products and structures. While they rarely destroy healthy hives, they cause catastrophic damage to weakened colonies or stored beekeeping equipment and wax products.
Identifying the Wax Moth Stages
The wax moth life cycle includes four phases: egg, larva, pupa, and adult. Adult moths are the reproductive stage. The Greater Wax Moth measures up to 19 millimeters long, while the Lesser Wax Moth is around 13 millimeters. Both species are pale brown or gray, holding their wings in a characteristic “roof-like” shape at rest. Adult moths do not feed and cause no direct damage to the comb.
Female moths lay tiny, spherical eggs in clusters within hive cracks and crevices. These eggs hatch into the destructive larval stage, which causes the damage. Newly hatched larvae are small and creamy white, developing into gray, caterpillar-like worms. The greater species’ larvae can reach a length of 28 millimeters.
The larvae burrow extensively through the comb; this tunneling is the first sign of infestation. Once fully grown, the larva seeks a protected location, often chewing an indentation into the wooden frames or hive body. Within this cavity, the larva spins a tough, silken cocoon, transforming into the pupa. The pupa is immobile and yellowish-brown, lasting one to nine weeks depending on temperature.
The Destruction of Honeycomb
Damage is exclusively caused by the larval stage, which consumes the comb for nutrients. While larvae can digest beeswax, they primarily seek protein-rich impurities within the wax structure. These components include stored pollen, shed larval skins, and cocoons from previous bee generations. This makes old, dark brood comb highly susceptible.
The larvae move through the comb by creating silken tunnels, known as galleries, lined with protective webbing. This tunneling physically destroys the cell structure, making the comb unusable for raising brood or storing honey. The webbing contaminates the honey and wax with larval feces and silk, rendering the product unmarketable and the comb unsalvageable.
In a live colony, a heavy infestation severely weakens the bee population by destroying the brood area. This sometimes results in “bald brood,” where cell caps are partially removed. Extensive webbing and destruction can stress the colony, causing them to abscond or abandon the hive. In stored equipment, larvae may bore into the wooden components of frames or hive boxes to pupate, causing permanent structural damage.
Managing and Preventing Infestations
The primary prevention strategy for active hives is maintaining strong, populous colonies. Healthy bees naturally defend against wax moth entry and remove eggs. Beekeepers should conduct regular inspections to identify signs of weakness or disease, which often precede an infestation. Removing excess, unused comb or wax debris from the apiary eliminates potential breeding sites.
Temperature methods are highly effective for controlling infestations in stored equipment and leave no residue. Freezing infested frames or wax products at 0°F (-18°C) for a minimum of 24 hours kills all life stages. Heat treatment can also be used, but it must be monitored carefully to avoid melting the wax.
Chemical and biological controls offer additional solutions for stored comb. The biological agent Bacillus thuringiensis (Bt) is a naturally occurring bacterium applied as a spray. When larvae consume the treated comb, Bt spores release a toxin that kills them, but it is harmless to adult moths, bees, and humans. Chemical fumigants, such as paradichlorobenzene (PDB) crystals, treat empty stored equipment. PDB is not safe for use on frames containing honey for human consumption and requires extensive airing out before being returned to a colony.