Greater Wax Moth (Galleria mellonella)

The greater wax moth (Galleria mellonella) is a night-flying moth whose larva feeds by tunnelling through the comb. In a strong colony the bees clear out the larvae; the real damage is seen in stored combs and in weak hives with too much space. Control is based on strong colonies, reduced hive space and correctly stored comb; substances that leave residues, such as naphthalene, are not used.

How to recognise it

• Adult moth: A grey-brown moth about 1.5–2 cm long that folds its wings like a roof. It flies at night and hides in cracks during the day; when disturbed it usually runs quickly rather than flying.
• Larva (caterpillar): Grey-white with a brown head; as it grows it reaches 2–3 cm. It has no spines on its back.
• Silk tunnels and webbing: White silk tunnels on the surface and in the middle of the comb, black crumbs of faeces.
• Cocoons: White silk cocoons packed tightly together on frame bars and hive walls; boat-shaped hollows are left in the wood beneath them.
• "Bald brood": Pupae with their heads showing, uncapped along a line where the larvae have passed beneath the cappings.

Life cycle and feeding

The female moth enters the hive at night and lays her eggs in cracks and gaps. The larvae that hatch enter the comb and tunnel through it as they feed; when mature, they spin a tough cocoon against the wood and pupate. Development depends on temperature: it takes a few weeks in hot summer conditions and months in cool conditions. This is why the damage explodes in summer and autumn.

The larva cannot develop well on pure beeswax. Its main food is the cocoon remains, pollen and impurities in dark combs in which brood has been reared. For this reason dark brood combs are the most damaged; light-coloured super combs that have never held brood and foundation attract it less.

How it differs from similar conditions

If you see a larva in the comb that makes you think of the small hive beetle, preserve the sample in alcohol and report it to the official veterinary service / local agriculture authority.

What to do in the hive

• Keep the colony strong. A strong colony clears out the larvae itself; seeing wax moth in a hive is often a sign that the colony has weakened or has too much space. Investigate the cause too: queenlessness, varroa, disease.
• Reduce the space. Remove frames the bees cannot cover and empty boxes.
• Unite weak colonies, seal cracks and clean the debris off the floorboard regularly.
• Sort out moth-infested combs. You can freeze lightly infested comb and use it; render down badly destroyed comb.
• Do not leave dead or abandoned hives open in the apiary. They soon become a source of wax moth.

Protecting stored comb

This is where the real battle is fought. Combs taken out of the hive after the harvest and during winter preparation can become unusable within a few weeks if they are not protected.

1. Sort them: Render down very old, dark and broken combs instead of storing them. Keep dark brood combs separate from super combs.
2. Freeze them: The safest way to kill all stages, including eggs, is to keep the comb in a deep freezer (-15 °C or colder) for at least 2 days.
3. Prevent reinfestation: After letting frozen combs dry, store them in closed boxes or hive bodies that the moth cannot enter.
4. Keep them cool, light and airy: The moth likes darkness, warmth and still air. A cold store and widely spaced, well-lit shelves markedly reduce the damage.
5. Biological protection: Authorised Bacillus thuringiensis (aizawai strain) preparations can be applied to comb for storage according to the label; they are effective against the larvae.
6. Regular checks: Inspect the store every few weeks during the warm months.

Perspective

In nature the wax moth is a useful decomposer: by clearing out old comb in abandoned nests, it prevents pathogens from building up. The problem in the apiary is not the presence of the moth but comb that the bees cannot protect or that is stored unprotected.