Bees are foundational to biodiversity and the world’s food supply, pollinating a substantial portion of the globe’s flowering plants and crops. Approximately one-third of the human food supply, including many fruits, vegetables, and nuts, depends on their pollination services. They support the growth of plants that provide food and habitat for countless other species. Despite their immense importance, bee populations face multiple serious threats, ranging from microscopic organisms to large-scale human activities that alter their environment.
Internal Biological Threats: Pests and Pathogens
The most significant single threat to managed honeybee colonies worldwide is the parasitic mite Varroa destructor. Recent research confirms these mites primarily consume the honeybee’s fat body tissue. This tissue is responsible for immune function, detoxification, and nutrient storage for winter survival. Feeding on the fat body severely weakens the bees, compromising their immune systems and making them susceptible to other diseases.
Varroa mites also act as a vector for debilitating viruses, most notably Deformed Wing Virus (DWV), which is considered a primary driver of colony failure. The physical injury from the mite’s feeding allows viruses to proliferate in the bee’s system. This often leads to workers being born with shriveled wings and shortened abdomens. This combination of physical damage, nutrient loss, and virus transmission makes the mite infestation a systemic problem that can lead to the rapid decline of an entire colony.
Other internal threats involve bacterial diseases that target the developing brood. American Foulbrood (AFB) is a highly lethal bacterial disease caused by the spore-forming bacterium Paenibacillus larvae. These spores are incredibly resilient, remaining viable for decades on old equipment and infecting larvae after they have been capped in their cells. European Foulbrood (EFB), caused by Melissococcus plutonius, is less severe but still contagious, often appearing when colonies are stressed from poor nutrition or unpredictable weather. Both foulbrood diseases lead to the death of the developing larvae, resulting in a spotty brood pattern and eventual colony collapse if left untreated.
External Biological Threats: Direct Predators
Direct predators typically pose a less systemic threat to a bee population than internal pests, but they can still cause localized damage and stress. Wasps and hornets are common hunters that often prey on adult bees as they return to the hive or raid the colony for protein, targeting larvae and pupae. Yellow jackets, for example, can become a nuisance, while larger species like the Asian Giant Hornet can decimate a hive’s adult population in a short period. This kind of predation usually results in the loss of individual foragers, which can slow the colony’s growth but rarely causes immediate collapse unless the attacks are overwhelming.
Mammals like bears and skunks are also drawn to bee colonies, primarily seeking honey and brood. Bears will often destroy a hive to access the honey stores and protein-rich larvae, causing massive damage to the physical structure of the colony. Skunks will scratch at the hive entrance to lure out guard bees, eating them individually until the colony’s defense is weakened. Spiders, such as orb-weavers, set up webs near floral resources to capture foraging bees, while crab spiders camouflage themselves directly on flowers to ambush unsuspecting visitors.
Anthropogenic and Environmental Factors
Human-caused factors represent the greatest existential threat to bees, as they weaken the insects’ overall health and resilience against all other enemies. The widespread use of systemic insecticides, particularly neonicotinoids, is a major concern. These chemicals are absorbed by the plant and present in the pollen and nectar that bees collect. Even at sublethal doses, neonicotinoids are neurotoxicants that interfere with the bee’s nervous system, which relies on acetylcholine for signaling.
Exposure to these chemicals impairs cognitive functions, including learning, memory, and spatial orientation. This neurological damage causes foraging bees to become disoriented, making them unable to navigate back to the hive, a phenomenon that leads to a significant loss of adult workers. The continuous exposure also weakens the immune system, leaving bees more vulnerable to the pathogens and mites discussed earlier.
Habitat loss and the resulting lack of diverse nutrition further compound these problems. Modern agricultural practices often favor monoculture, where a single crop is grown over vast tracts of land. While mass-flowering crops can provide temporary forage, this practice drastically reduces the variety of pollen and nectar sources available to bees. Bees require a diverse diet to obtain all the necessary proteins, lipids, and micronutrients, and a single-source diet can lead to nutritional stress and a compromised immune system.
Urbanization and industrial farming also lead to habitat fragmentation, eliminating natural nesting sites and forcing bees to travel greater distances for food. Climate change introduces another layer of environmental stress by altering the timing of natural events. Unpredictable weather patterns and warming temperatures can cause a “phenological mismatch,” where plants bloom earlier than the bees emerge from their overwintering stage. If bees emerge when their primary food sources have already flowered, they face a period of starvation, which directly impacts their survival and reproductive success.