Bees are recognized globally for their services in pollination, which is integral to ecological stability and the world’s food supply. Factors that threaten their survival fall into two broad categories: immediate biological pressures and large-scale environmental stressors. Biological enemies include parasites, pests, predators, and diseases that directly attack the individual bee or the colony. Environmental threats, largely driven by human activity, are more systemic, weakening bee populations and making them vulnerable to biological dangers. The complexity of these interacting pressures is responsible for the significant colony losses observed worldwide.
Parasitic Mites and Internal Hive Pests
The most destructive biological enemy to the Western honeybee is the microscopic parasite Varroa destructor. This external mite attaches to adult bees and developing pupae, feeding on the bee’s fat body tissue, which is involved in immunity and metabolism. The mite acts as a vector for debilitating viruses, most notably Deformed Wing Virus (DWV). DWV causes severe symptoms like crippled wings and shortened lifespans, often leading to the rapid collapse of the entire colony.
Other internal pests compromise the colony’s health and resources. The Tracheal Mite, Acarapis woodi, infests the breathing tubes of adult bees, piercing the tracheal walls to feed on their hemolymph. This infestation reduces a bee’s ability to fly and shortens the adult bee’s lifespan.
The Small Hive Beetle (Aethina tumida) is a scavenger that thrives in weakened colonies. Its larvae tunnel through comb and defecate in the honey, introducing a yeast that causes the honey to ferment and “slime out.” This renders the food source unusable and often causes the bees to abandon the hive.
The Wax Moth (Galleria mellonella) is another hive invader whose larvae target the wax and protein-rich debris in the comb. The larvae tunnel through the wax, lining their paths with silken webs that destroy the comb’s structural integrity. In severe cases, the silk webbing can trap emerging bees, further weakening the colony’s population.
Natural Predators
Bees face numerous external predators that actively hunt and consume them or raid the hive for food stores. Predatory insects, like the invasive Asian Giant Hornet (Vespa mandarinia), pose an intense threat, using large mandibles to decapitate adult bees in the “slaughter phase.” A scout hornet marks the hive entrance with a pheromone, attracting nestmates for a mass attack to steal the protein-rich brood. The Yellow-legged Hornet (Vespa velutina) employs “hawking” by hovering near the hive entrance and capturing foraging bees as they return.
Vertebrate predators also target bees, often using specialized methods to overcome defenses. Skunks, protected by thick fur, scratch at the hive entrance at night, prompting guard bees to emerge. The skunk scoops up the bees, chews them to extract the internal contents, and discards the empty exoskeletons. Bears are primarily drawn to beehives not for the honey, but for the protein content of the bee brood, which they access by tearing apart the hive structure. Birds like bee-eaters capture bees in mid-flight and strike the insect against a perch to remove the stinger before swallowing their prey.
Major Pathogenic Diseases
Diseases caused by bacteria, fungi, and microsporidian parasites are significant, often targeting the vulnerable larval or adult stages. American Foulbrood (AFB), caused by the spore-forming bacterium Paenibacillus larvae, is one of the most severe bacterial threats. Larvae ingest the spores and die after their cell is capped, resulting in sunken, greasy-looking cappings and a characteristic “ropey” consistency when tested. The resulting dark, highly adhesive scale is nearly impossible for bees to remove, making AFB a persistent and devastating disease.
European Foulbrood (EFB), caused by Melissococcus plutonius, is generally less catastrophic but still damaging, attacking the larva before it is capped. Infected larvae appear twisted, yellow, or brown, and often melt into a rubbery scale that is easily removed by worker bees. This bacterium competes with the developing larva for nutrients, leading to death from starvation.
Chalkbrood is a fungal disease caused by Ascosphaera apis, where spores are ingested by young larvae. The fungus grows inside the larva, mummifying it into a hard, chalk-like pellet that can be white or black. These mummies can produce a distinctive rattling sound when the infected comb is shaken.
Nosema disease, caused by the microsporidian parasites Nosema apis and Nosema ceranae, infects the digestive system of adult bees. This infection shortens the lifespan of adult bees, can cause dysentery, and forces young nurse bees to become premature foragers, which reduces the colony’s strength.
The Impact of Human Activity
Large-scale human practices represent the most pervasive and challenging long-term threats to both managed and wild bee populations. The use of systemic insecticides, particularly neonicotinoids, has a profound neurotoxic effect on bees, even at sublethal concentrations. These chemicals impair cognitive functions by acting as agonists of the nicotinic acetylcholine receptors in the insect brain. Studies have shown that exposed bees suffer from a disrupted homing instinct and memory, leading to an inability to navigate back to the hive and a reduced successful return rate.
Modern industrial agriculture, characterized by monoculture farming, severely limits the diversity of food available to bees. Vast fields of a single crop provide only a brief period of nectar and pollen, followed by a nutritional desert. This lack of diverse forage results in a poor diet, which compromises the bees’ immune systems and makes them more susceptible to diseases and parasites. Habitat loss and fragmentation further exacerbate this problem by removing the natural corridors of wildflowers that bees rely on for diverse nutrition and nesting sites.
Climate change is a systemic threat that contributes to a phenomenon known as phenological mismatch. As global temperatures rise, the timing of spring blooming shifts earlier, but the emergence or peak abundance of worker bees does not always accelerate at the same rate. This difference in response timing creates a gap between when the bees need resources and when the flowers are available, leading to periods of resource scarcity and starvation.