Finding dead bees is common. While a few dead bees are part of their natural life cycle, larger numbers or unusual circumstances can signal underlying issues. Understanding the causes of bee mortality helps interpret these observations and determine appropriate actions.
Natural Bee Mortality
Bees have a finite lifespan, and individual deaths are normal within a colony. Worker bees typically live for about five to seven weeks during active seasons like spring and summer. Their short lives are often marked by exhaustion from constant foraging.
Harsh weather conditions, such as sudden cold snaps, extreme heat, or severe storms, can also lead to bee deaths. Bees caught outside the hive during adverse weather, or those unable to regulate hive temperatures, may succumb to the elements. Natural predators, including birds, spiders, and other insects, contribute to the daily mortality of bees. Observing a small number of dead bees around a hive or in a garden is a normal aspect of a healthy, active bee colony.
Environmental and Human-Induced Causes
Beyond natural mortality, several environmental and human-induced factors can lead to significant bee deaths. These issues often weaken bee colonies, making them more susceptible to disease and other stressors.
Pesticide exposure is a major contributor to bee decline. Systemic insecticides, particularly neonicotinoids, are absorbed by plants and can be present in pollen and nectar. Bees can also be exposed through direct spray, contaminated water sources, or contact with treated dust during planting. Exposure to these chemicals can lead to disorientation, impaired navigation, paralysis, and ultimately, death, even at low concentrations.
Diseases and parasites also devastate bee populations. Varroa mites (Varroa destructor) are external parasites that feed on bees and can transmit debilitating viruses, such as deformed wing virus. These mites are considered one of the most damaging bee pests globally, often leading to colony collapse within two to three years if left unmanaged. Bacterial diseases like American Foulbrood (AFB), caused by Paenibacillus larvae, and European Foulbrood (EFB), caused by Melissococcus plutonius, primarily affect bee larvae, leading to their death. Nosema, a microsporidian fungus, infects the digestive systems of adult bees, causing weakness, dysentery, and a shortened lifespan.
Habitat loss and malnutrition further compromise bee health. The expansion of agriculture and urbanization has resulted in the destruction of natural landscapes, replacing diverse floral resources with monoculture farming or paved areas. This reduction in varied food sources limits essential nutrients, weakening bees and making them more vulnerable to diseases and pesticides. Lack of suitable nesting sites also impacts bee populations.
Climate change introduces additional pressures on bee colonies. Altered weather patterns, including extreme heatwaves, droughts, and floods, disrupt foraging activities and can destroy food sources and nesting habitats. Changes in flowering times, where plants bloom earlier or later, can create a mismatch with bee emergence and foraging cycles, leading to nutritional stress. Warmer fall and winter temperatures can also extend the period when bees forage, potentially increasing the spread of Varroa mites and the viruses they carry.
Interpreting the Signs
Observing the circumstances surrounding dead bees can offer clues about the cause of mortality. The quantity and location of dead bees are important indicators; a few scattered dead bees are normal, but large numbers, especially clustered near the hive entrance, may signal a problem. Piles of dead bees with their tongues, or proboscis, extended can suggest pesticide poisoning. Bees affected by pesticides might also exhibit disorientation, trembling, or an inability to fly.
The appearance of the dead bees themselves can provide further insight. Discolored or deformed bees, or those with unusual postures, might indicate disease or chemical exposure. For instance, larvae affected by European Foulbrood may appear curled, yellowish-brown, or melted, while American Foulbrood causes larvae to become dark brown and “ropy.” Fecal streaking on or around the hive can be a sign of Nosema infection. The time of year also matters; unusual die-offs during foraging season are more concerning than winter losses. Observing recent activities in the area, such as nearby pesticide applications, new construction, or unusual weather events, can help connect observations to potential causes.
Supporting Bee Health
Individuals can take several steps to support bee health, especially if non-natural causes of mortality are suspected. Planting a diverse array of bee-friendly flowers provides a continuous food source. Prioritizing native plants can be beneficial as they are well-adapted to local ecosystems and provide optimal nutrition.
Minimizing or avoiding pesticide use in gardens and yards significantly reduces bee exposure to harmful chemicals. If pest control is necessary, exploring non-chemical alternatives or using pesticides with the least impact on pollinators is recommended, always applying them according to label instructions and during times when bees are not active. Providing clean water sources, such as a shallow dish with pebbles or marbles for bees to land on, offers a safe hydration point.
Supporting local beekeepers promotes sustainable beekeeping practices, which are vital for maintaining healthy honey bee populations. In cases of significant bee mortality, especially if a large number of dead bees are found or pesticide poisoning is suspected, report the incident to local extension offices, beekeeping associations, or environmental agencies like the EPA. These organizations can investigate the cause and help implement measures to protect bee populations.