Dead Bees

three dead bees outside hive
Dead bees can be caused by various factors including weather, climate change and diseases

During the last several years, there’s been an average annual loss of 30% of the world’s bees. In 2019, that percentage was closer to 40%. There are several reasons as to why bees are dying, but it is possible to prevent some of these causes of death – or even improve their populations.

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    What Causes Bees to Die?

    Around 2006, there was a reported rise in the phenomenon of “vanishing bees” or what had been termed Colony Collapse Disorder (CCD). With CCD, the majority of worker bees are found to have left the queen behind with only a few workers to care for the developing brood. 

    Although that phenomenon had been seen in earlier years, the uptick in disappearing colonies during the early 2000s turned into a global concern that coincided with the discussion of the overall decline in bee populations.

    Although CCD is not as big of a problem these days, there is still reason to be worried about real threats that can cause bee death. The major threats facing bees today are parasites, pesticides, poor nutrition, predators, disease, and climate change.

    Can Parasites Affect Bees?

    Parasites are a real threat to many species of bees – particularly honey bees. The varroa mite has been especially harmful in recent years and continues to be a threat if mitigation is not offered. 

    The varroa mite is only around 1.2 millimetres but is very destructive. It will wedge itself between the exoskeletal plates of the bee and release enzymes through its mouthparts to break down tissues. It feeds on the blood of adult bees, but also larvae and pupae. 

    The varroa mite is considered to be the most serious parasite affecting bees, but there is another notable one. Acarapis woodi is a mite that infests the breathing tubes – or tracheae – of honey bees. They use their mouthparts to break through the tracheal tubes and feed on bees’ blood.

    Colonies can die within a couple of years unless beekeepers take action to stop these parasites.

    Are Predators a Threat to Bees?

    It appears that bumblebees are especially attractive to predators. Badgers use their claws to dig up bumblebee nests and eat both the food stores and larvae. While birds don’t dig, they will often eat bees that are outside of the nest.

    Bumblebees are also threatened by spiders. The Crab spider waits for a bumblebee to approach a flower, then grabs the bee and injects it with a powerful venom that causes paralysis and death.

    Honey bees are threatened by predators like bears, skunks, and hive beetles. More recently, news of Vespa mandarinia – or murder hornet – has sparked fear among humans due to reports of its extremely painful sting. 

    But it is actually honey bees that are more threatened by this predator. Vespa mandarinia will crawl into hives and rip off the heads of large numbers of honey bees, which is a huge concern for the agriculture industry that depends on these bees for pollination.

    Goldenrod crab spider eating a bee

    Are Bees Threatened by Disease?

    Both adults and developing broods can be decimated by disease. Some of the adult diseases include:

    • Viruses that cause paralysis, such as chronic bee paralysis virus (CPV) and acute bee paralysis virus (APV)
    • Pollen and nectar from plants like buttercup, rhododendron, basswood, and laurel
    • Nosema disease, which invades the digestive tracts of honey bees


    Some common brood diseases are:

    • American foulbrood, which is caused by a spore-forming bacterium
    • European foulbrood, which can multiply rapidly in the gut of a larva
    • Chalkbrood – caused by a spore-forming fungus
    • Sacbrood – a virus that often goes unnoticed since it impacts only a small proportion of the brood, but can be a serious concern if the adult bees don’t remove the infected larvae.

    Do Pesticides Kill Bees?

    Pesticides are controversial since they are absolutely necessary for minimizing the number of insects that can destroy crops but have harmful health consequences for insects that are not part of the targeted population.

    Neonicotinoids are a class of insecticide that is the most widely used throughout the world – in over 120 countries. Because they are taken up by all or parts of the plants as they grow, neonicotinoids can certainly impact pollinators when they forage among these plants. The nectar and pollen that bees bring back to their hives or nests are undoubtedly contaminated by the presence of these pesticides. 

    Researchers have found an average of three or four chemicals in bee colonies and as many as fourteen. It is difficult to know what are the impacts of all of these different chemicals in combination.

    But studies have found that it may be bumblebees that are most impacted by these pesticides, even though much more attention has been paid to their effect on honey bees. In fact, bumblebees are two to three times more sensitive to neonicotinoids than honey bees.

    Pesticides used to manage parasites as the varroa mite can also impact bee health. A 2007 study found that the fungicide used to thwart that harmful parasite was found in the bee bread of honey bee colonies. Until more research is done, we will not know whether the substances used to control parasitism will have negative consequences for the overall health of a bee colony.

    How Does Poor Nutrition Affect Bees?

    It is entirely possible for bees to starve. When they don’t have adequate access to pollen and nectar, their nutrition will suffer. And it’s not only a lack of resources in total but the absence of diversity that can cause nutritional deficiencies.

    Much of this problem is due to letting the agriculture industry use a vast portion of available land to grow only one or a limited number of crops. Planting the same types of crops in the same place every year not only suppresses biodiversity but can also weaken the soil and increase the likelihood of plant diseases and pathogens.

    The nectar of the Silver Linden tree doesn't contain enough nutrition, causing the bees to starve from consuming it

    Can the Weather Kill Bees?

    Bees are vulnerable to weather threats like unexpected cold snaps, extreme heat, and flooding. Without their protective hives or nest, bees can be harmed not only by the direct impact of the particular weather system but also due to an absence of food while they are stranded or grounded.

    But it is not just one-off weather systems that are impacting bee health. Climate change can affect long-term weather patterns that can alter seasonal reproductive schedules and the availability and quality of food sources.

    Why Are There Often Large Numbers of Dead Bees Under Lime/Linden Trees?

    Occasionally, large numbers of dead bumblebees are seen under Linden (or Lime) trees. When this phenomenon was first spotted, scientists began to study what might be the cause. 

    It was originally thought that there was a toxic carbohydrate in the nectar, but it was eventually discovered that the nectar of a particular tree – Tilia tomentosa – lacked the nutrition the bees needed and they were literally dying due to poor nutrition. 

    Additionally, as the bees metabolize the nectar it can cause them to become addicted to it, and they will continue feeding even though they’re not getting the energy they need. If the bees rely only on those particular trees as a source of food, they will starve to death.

    Why Are There Dead Bees on the Window Sill?

    If there is a dead bee on the window sill, the most likely cause of death is that the bee was trapped in the house – away from the hive or nest that provides its nutritional needs. A bee has only about an hour of flying time on a full stomach, so if the bee is trapped for a long period of time, it won’t have the energy to survive. Once a bee is trapped in the house, it will likely die within a few hours.

    Dead bees on the window sill most likely mean that they got trapped inside the house and died from starvation

    How Many Bees Die From Road Collisions?

    There’s a simple reason why some people notice large numbers of dead bees along busy highways or on bridges over well-travelled roads. Municipalities often plant flowers on medians or road verges, and bees are putting themselves in danger in order to forage there.

    Planting on these verges does beautify the roadway and many may think they are helping out pollinators by providing floral resources. But more studies should be conducted to determine whether or not a particular location could cause more harm than good. It’s thought that billions of insects could die annually as a result of traffic collisions.

    What Can the Average Person Do to Help Reduce Bee Deaths?

    The largest contribution humans can make to improve bee health is to plant flowers. It is best not to use pesticides or to be more thoughtful about which ones to choose.

    People can also help by leaving some of the plants that crop up on the lawn – like dandelions or other wildflower types of weeds. 

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