The Enemies of the Hive: Mites, Hornets, Moths and the Other Threats Bees Face

The single biggest threat: Varroa destructor

If there is one organism responsible for transforming beekeeping worldwide over the last four decades, it is Varroa destructor, a parasitic mite originally native to Asian honey bees (Apis cerana) that jumped to the European honey bee (Apis mellifera) roughly a century ago and has since spread to nearly every honey-bee-keeping region on Earth. The mite reproduces inside sealed brood cells, entering just before a cell is capped and laying eggs on the developing larva, with reproduction succeeding at notably higher rates in drone brood than worker brood — one reason drone brood is sometimes used as a deliberate mite "trap" that beekeepers can remove and destroy.

Varroa's damage isn't limited to the physical feeding itself; the mite is also an extremely efficient vector for viruses, most notably deformed wing virus (DWV), which can leave emerging bees with shrivelled, non-functional wings and shortened lifespans. Left unmanaged, a Varroa infestation can escalate from a minor nuisance to a colony-collapsing crisis within a single season, which is why Varroa monitoring and treatment has become the single most important recurring task in modern beekeeping.

Bees do have some natural defences. Hygienic behaviour — the tendency for workers to detect and uncap infested brood cells and remove the pupa before the mite can complete reproduction — is a genetically selectable trait, and a specialised, more targeted version called Varroa Sensitive Hygiene (VSH) has been deliberately bred into some commercial bee lines. Mutual grooming between workers also physically dislodges some mites. Beekeepers supplement these natural defences with treatments such as oxalic acid (most effective when applied during broodless periods, since it only kills mites riding on adult bees rather than mites sealed inside brood cells) and various miticide strips, alongside management techniques like deliberately breaking the brood cycle for a few weeks to interrupt mite reproduction.

Wasps and hornets: robbers and predators at the entrance

Several wasp and hornet species prey on or rob honey bee colonies, with the severity ranging from a mild seasonal nuisance to an existential threat. Common wasps (Vespula species) mostly pose a robbing risk rather than a direct predation threat: when a colony is already weak or its guard force is thin, wasps will attempt to enter and steal honey stores, and if successful, can recruit more wasps to the raid, sometimes escalating into a full robbing frenzy that a weakened colony cannot repel and that can strip out its stores within days.

The European hornet (Vespa crabro) is a more direct predator, individually hunting returning foragers at the hive entrance, particularly active at dusk when European honey bees become sluggish. A strong colony with an alert guard force can usually mob and repel individual hornets effectively, but persistent late-summer and autumn hornet pressure can measurably reduce a colony's forager numbers and its ability to build up winter stores.

Far more serious is the Asian giant hornet (Vespa mandarinia), and its smaller relative the Asian hornet (Vespa velutina) which has been spreading through parts of Europe including sightings in the UK. Asian giant hornets can shift from individually hunting foragers to a coordinated "slaughter phase," in which a small group of hornets systematically kills every bee in a colony — sometimes tens of thousands of bees within a few hours — in order to take over the hive and harvest the brood to feed their own larvae. European honey bees have essentially no effective defence against this behaviour, since a hornet's thick cuticle makes individual bee stings largely ineffective. By contrast, Japanese honey bees (a different Apis cerana population) have evolved a remarkable defence: hundreds of workers swarm around an invading hornet and vibrate their flight muscles to raise the temperature at the centre of the ball to around 46–47°C, a temperature the hornet cannot survive but that the bees themselves can just barely tolerate — a striking example of a coevolved defence that simply hasn't had time to develop in bee populations recently exposed to this predator.

Wax moths and small hive beetles: opportunists that thrive on weakness

The greater wax moth (Galleria mellonella) and lesser wax moth (Achroia grisella) are less dramatic but genuinely damaging pests. Adult moths lay eggs inside a hive, often exploiting small gaps at night, and the resulting larvae tunnel through comb, consuming wax, pollen and the remains of brood cells while leaving behind extensive silk webbing that renders comb unusable. Crucially, wax moths are almost exclusively a problem in already-weakened colonies; a strong, populous colony will detect and remove moth larvae and eggs long before they can establish, which is why wax moth damage is often better understood as a symptom of an underlying colony weakness — such as Varroa damage, disease, or queen failure — rather than a primary cause of collapse on its own. Stored, unused comb is particularly vulnerable and beekeepers typically protect it in cold storage, since freezing reliably kills all life stages of the moth.

The small hive beetle (Aethina tumida), native to sub-Saharan Africa, has become an invasive pest in parts of North America, Australia and elsewhere. Adult beetles hide within the hive, often in propolis-sealed crevices where guard bees can harass but not kill them — a behaviour beekeepers sometimes call "beetle jailing" — while larvae tunnel through comb and defecate in stored honey, causing it to ferment and become unusable. In warm climates, beetle populations can explode extremely quickly under favourable conditions, and control typically combines in-hive traps with insecticide treatment of the soil around the apiary, since beetle larvae leave the hive to pupate in the ground nearby.

Brood diseases: bacteria, viruses and fungi

Beyond mites and larger predators, honey bee brood is vulnerable to a range of bacterial, viral and fungal diseases, several of which are serious enough to be legally notifiable in the UK and many other countries, meaning beekeepers are required to report suspected cases to the relevant bee health authority (in the UK, the National Bee Unit).

• American foulbrood (AFB), caused by spore-forming bacteria (Paenibacillus larvae), is the most serious brood disease — it produces sunken, perforated cell cappings and a characteristic "ropy" texture when a matchstick is drawn through affected larval remains, and because its spores can remain viable for decades, infected colonies and equipment in the UK are typically required to be destroyed by burning rather than treated.
• European foulbrood (EFB), caused by a different bacterium (Melissococcus plutonius), is also notifiable and generally less severe than AFB but still requires prompt reporting and management, often including antibiotic treatment under veterinary guidance or destruction of severely affected colonies.
• Chalkbrood, a fungal disease, causes larvae to become hard, white or black "mummies," and thrives particularly in damp, poorly ventilated hives, generally causing moderate rather than severe colony impact.
• Sacbrood virus causes affected larvae to fail to pupate properly, appearing as a fluid-filled sac with a characteristically darkened head, and typically causes mild to moderate colony impact rather than a serious threat on its own.

Vertebrate predators: bears, badgers and woodpeckers

Away from insects and microbes, honey bee colonies also face predation and disturbance from larger animals depending on region. In parts of North America and Europe, bears remain a serious hive-destroying threat, particularly in early spring when food is scarce or in late summer if other food sources fail, and a single determined bear attack can completely destroy a hive in one visit; electric fencing is by far the most effective deterrent. In the UK specifically, badgers occasionally dig at and disturb hives at night, dislodging floors or covers and letting in cold air that can chill and kill brood, which is why many beekeepers use hive straps and raised stands to make hives harder to tip or access. Woodpeckers, particularly during hard winters when other food is scarce, can peck through wooden hive walls seeking overwintering bees and stored honey, and are usually deterred with wire mesh wrapped around the hive during the colder months.

How guard bees mount a coordinated defence

Whatever the threat, individual bees don't defend the colony alone — defence is a coordinated, graded response involving pheromone communication. Guard bees stationed at the entrance patrol and inspect every arriving bee, checking its cuticular hydrocarbon scent profile (a chemical "ID badge" unique to the colony) to identify intruders. An unrecognised or threatening presence triggers escalating responses: guards may block entry and buzz aggressively, chase an intruder away from the hive, or, if the threat persists, release alarm pheromone (isopentyl acetate, sometimes described as smelling faintly of bananas) that recruits additional guards and can, in a serious threat, mobilise a large fraction of the colony's population to swarm out and attack collectively — a response usually reserved for genuinely severe threats like a hornet attack or a large mammal disturbing the hive, since every bee that stings in defence of the colony dies in the process.