Causes Of Bee Population Loss & Decline (Why Are Bees Dying)

We’ve already put together a guide discussing whether bees are endanagered and whether they will go extinct

In the guide below however, we outline what some of the causes of bee population loss and decline might be.


Summary – Causes Of Bee Population Loss & Decline

Population Decline vs Endangerment vs Extinction

There’s a different between population decline, endangerment, and extinction

A decline is a general decrease in the population over a specific time period, without the population being endangered or going into extinction

Endangerment is a decline in the population to the point population numbers are low enough that the species is considered an ‘endangered species’ and is usually added to the endangered species list in that region

There’s a small number of species of bees that have been placed on the endangered list in some regions of the world

Extinction is a complete termination or loss of the species


Temporary vs Permanent Population Decline

Some population declines only last a year, or a few years, before population numbers stabilise and/or increase again. These are temporary declines

Permanent declines are year on year declines that last for a specific period, and may lead to the endangerment or extinction of the species


It’s also worth noting that bee population numbers can go up and down seasonally – honey bee loss for example is expected over the winter months.


Population Loss/Decline Causes

There’s various potential causes of bee population loss and decline

We’ve listed an array of potential causes below, relating to the endangerment of certain bee species, the temporary decline of some bee species, and some general bee population loss factors


Each Species In Each Location Can Be Different

Each individual species of bee in each geographic location around the world can have different factors that impact on population increase or decline, over different time periods

Therefore, each species in each location requires a separate analysis of the main causes of population decline in the event that this is happening during a specific time period


Challenges In Assessing Population Numbers

Sometimes the tools available to local agencies to study bee population decline are not as good as they could be, and can be deficient in some ways

There might be room to improve this to get more accurate data


Potential Solutions To Saving Bee Populations

There may also be ways to preserve bee numbers and populations in specific regions around the world


Are Bees Endangered Or At Risk Of Extinction?

According to available information, a very small number of species of bees might be endangered in certain parts of the world, but American honey bees are not yet on the endangered list, and neither are majority of bee species in the world.

In the recent past, there hasn’t been any bee species that has reached extinction.


Have Bee Population Numbers Declined?

A bee species’ population can experience a temporary decline over a multi year period for any one reason or multiple reasons, without experiencing a permanent decline.

Temporary population declines have happened with some major bee species over time in some places.

In the case of a species of bee being put on the endangered list, this generally involves a more permanent decline.


Causes Of Bee Population Loss & Decline

It really depends on the region and bee species as to what the main causes of bee population loss and decline are.

For example, the threats facing the Hawaiian yellow faced bees might be different threats facing US honey bees.

The time period over which bee population numbers are declining also matters – different periods of incline and decline can have different factors at play. indicates that ‘There is no one single factor that causes bee numbers to drop (when they do), but rather a combination of factors’


Causes Of Hawaiian Yellow Faced Bee Species’ Endangerment

A group of bee species that have been noted as being endangered in the recent past was the Hawaiian yellow-faced bees species.


According to, some of the threats that the Hawaiian Yellow Face bee populations face are:

‘… habitat destruction because of urbanization or non-native animals, the introduction of nonnative plant species, wildfires, nonnative predators and natural events such as hurricanes, tsunamis and drought’


Causes Of Rusty Patched Bumble Bee Species Endangerment

Another bee species that has been noted as being endangered in the recent past is the Rusty Patched Bumble Bee. also notes that:

… recently, in addition to the Hawaiian yellow-faced bees, the Rusty patched bumble bee has been placed on the endangered list too.

They note ‘habitat loss, natural disasters, and invasive species [are believed to be the causes].’


Causes Of US Honey Bee Temporary Population Decline

US honey bee population numbers temporarily dipped for a few years during the Colony Collapse Disorder trend (for roughly 3-5 years, with the first signs appearing in 2006 in California).

But, since then they have been increasing, and have been steady overall throughout history.


In general, the threats and factors that cause US Honey Bee population numbers to drop when they do are thought to be:


Main Causes 

– Varrora Mites

Varrora mites that feast on bees, and the viruses these mites carry … they bring roughly a dozen different diseases into beehives, and the widely prevalent gut fungus, Nosema ceranae (

They also bring a virus that deforms bees’ wings (


Varrora mites can also become very resistant to miticides – so, there can be significant problems trying to control them and eliminate them.


– Poor Nutrition, Which Can Also Lead To Poor Health

Poor nutrition can be a factor/cause in itself, but it can also be a contributing factor to poor health.



Poor nutrition in the bees’ diet … they don’t eat enough of a variety of nutritious food sources.

They tend to get nutrition from one crop such as almonds which is farmed in a monoculture, and sugar water or corn syrup that beekeepers feed them) express how important bee health and nutrition is to fighting off other causes of bee sickness and death:

‘… pollen and nectar [is] collected from flowering plants [and contains] nutrients necessary for growth and survival.

Honey bees with access to better and more complete nutrition exhibit improved immune system function and behavioral defenses for fighting off effects of pathogens and pesticides

Bee colonies are chronically exposed to parasitic mites, viruses, diseases, miticides, pesticides, and poor nutrition, which weaken and make innate defenses insufficient at overcoming these combined stressors

Colonies that are chronically weakened can be even more susceptible to infections and levels of pesticide exposure that might otherwise be innocuous, further promoting a downward spiral of health.

Sick and weakened bees diminish the colony’s resiliency, ultimately leading to a breakdown in the social structure, production, efficiency, immunity, and reproduction of the colony, and eventual or sudden colony death’


– Not Getting A Variety Of Pollen

They don’t get a variety of pollen that stimulates resistance to disease (

The end result is that bees are weakened, and more susceptible to illness, disease and death from the other factors and causes.


Sub Causes  

– Pesticides & Insecticides

Pesticides … synthetic insecticides called neonicotinoids used to spray crop seeds – bees come into contact with these chemicals during pollination and carry it back to the hive. These types of pesticides have sometimes shown to short-circuit bees’ memory and navigation (

Insecticides used to kill varrora mites (also usually synthetic)


However, writes this about some sources claiming pesticides are the main cause of honey bee deaths:

‘… despite over a decade of study, it’s still yet to be proven that they’re [pesticides] playing a significant role in honeybee deaths’


Other Causes

– Winter

Winter causing bee numbers to drop naturally compared to summer months/warmer times of the year

This is a seasonal cause


– Colony Collapse Disorder

Colony collapse disorder (a short multi year period where US honey bee numbers decreased due to various factors)


– Habitat Loss

Habitat loss of lower meadows because of urban development


– Lack Of Financial Incentive To Protect Bees

From Although people on farms and in cities are ready and willing to take action to protect bees and other beneficial insects, their actions are impeded by a lack of financial incentives …


– Lack Of Abundant Seeds For Pollinator Habitats

From Although people on farms and in cities are ready and willing to take action to protect bees and other beneficial insects, their actions are impeded by a … lack of abundant seeds to plant pollinator habitat on large scales …


– The Knowledge, Strategy & Actions Of Inexperienced Amateur Beekeepers

Inexperienced amateur beekeepers having a higher bee loss rate than bigger or more professional beekeepers with more experience and resources



Although people on farms and in cities are ready and willing to take action to protect bees and other beneficial insects, their actions are impeded by a … lack of education about ways to protect pollinators while applying pesticides.


– Other Mites & Beetles

Such as Acarina Mites and Hive Beetles


– Diseases

Bee diseases such as foulbrood and chalkbrood (which are made higher risk by bees having a poor diet)


– A Changing Climate

Climate change and a changing global average temperature (although this is more a ‘maybe cause than a definite cause) – changing temperatures can push bees’ physiological limits, change hive behavior, can change their eating and feeding patterns, and can force them to go find new habitats where it’s more mild in temperature


What Factors Are Less Likely To Be The Cause Of Bee Population Loss? discusses the temporary honey bee decline, and indicates what might be some likely causes, and unlikely causes:

It’s likely that [the loss of bees is not due to …] GMOs, cellphones, ultraviolet lights, electromagnetic radiation

It more likely to be a combination of factors that include parasites, pathogens, pesticides, poor nutrition, and habitat loss


What Specifically Caused The 44% Decline In The US Honey Bee Population In 2015/16? describes the potential causes of the 44% decline in the US Honey Bee population in 2015/16:

… many factors are contributing to colony losses.

A clear culprit is the varroa mite, a lethal parasite that can easily spread between colonies. 

Pesticides and malnutrition caused by changing land use patterns are also likely taking a toll, especially among commercial beekeepers

Varrora is a particularly challenging problem among backyard beekeepers (defined as those who manage fewer than 50 colonies).


The Potential Challenges & Difficulties In Identifying Bee Population Decline Causes, & Reporting Population Number Trends makes a point about how it can be difficult to pin point what the main causes of bee decline might be in a particular area over a multi year period:

‘… mechanisms for reporting colony losses and identifying the source of contamination are deficient and variable based on state and local government agencies


Additionally, some other challenges when it comes to counting bee numbers and pollinator species numbers might include:

– We can only get a measure on numbers of bees from colonies and hives of beekeepers – it’s impossible to measure wild bee numbers accurately

– There are other pollinator species other than bees – but, only a small number have hives that we can count numbers from














' ); } ?>

Leave a Comment