Challenges Facing Pollinators

In the modern world, pollinators are facing a wide variety of problems including habitat loss, climate change, pesticides, diseases, parasites and predators. Click on the tabs below to learn more:

Habitat Loss

Habitat is a place that provides the resources necessary for a living creature to thrive. The life cycles of pollinators are strongly tied to a variety of resources that habitats provide.  These include: host plants (specific species of plants required by some insects for food), pollen and nectar that provide protein, fats and sugars for bees, places to nest, places to seek shelter from predators, and places to overwinter. Cities and farmland have replaced much of the natural habitat in the prairies. This makes it more difficult for pollinators to find what they need to survive.

picture of a city landscapeHabitat loss comes in different forms. We are probably most familiar with its extremes, such as the conversion of a natural site to concrete, the felling of a forest, the ploughing of grassland, or the damming of a river.  However, there may also be habitat loss through changing one type of natural area to another kind of greenspace. A mowed yard or a manicured park might provide habitat for some species, but the highly altered area cannot provide the resources necessary to support a diverse community of pollinators.


Climate Change

Increased carbon emissions are changing how the natural world behaves. Some of the effects of climate change include severe, unpredictable, or unseasonable weather conditions, increased rains and flooding, extended droughts, intense wildfires, and an increase in invasive species.picture of a smoke stack

Climate change can alter the habitats where pollinators are found, and can also influence the long-term environmental patterns that many living things are accustomed to coping with. For example, insects that overwinter in leaf litter do best with a good snowpack for protection. If winter temperatures increase and snowpack is poor, they may be damaged from dry winter winds, or from the shifts between mild to freezing temperatures that are normally buffered by snow cover. Overwintering insects in milder temperatures may also be metabolically active when they should be inactive, burning their energy reserves too quickly. This makes it harder for them to survive until spring.

Some of the most well-documented impacts of climate change are the resulting mismatches between bloom times and insect emergence. Climatic conditions influence how early flowers open in spring, and when pollinators become active after overwintering. If the two events do not overlap, it can be disastrous for both plant and pollinator. The pollinator may emerge when few sources of pollen and nectar are available, limiting the growth and development of their offspring. The plants that bloom when no pollinators are available to visit miss the opportunity to cross-pollinate.  The negative effects of “flowering asynchrony” may be greatest for specialist plants and pollinators (those that rely on a certain species to survive), or in regions where the species are at the edge of their range and tolerance of environmental change.


What are Pesticides? Pesticides are broadly defined by Health Canada as “any product, device, organism or substance that is manufactured, represented, sold or used as a means for directly or indirectly controlling, preventing, destroying, mitigating, attracting or repelling a pest.” Commonly used pesticides include insecticides for controlling insects, herbicides for controlling weeds, and bactericides and fungicides for controlling various diseases in plants.  

Since most pollinators are insects, the insecticides present the biggest threat to their survival. The same compounds designed to be toxic to pest insects are often also toxic to beneficial ones. In some instances, herbicides and fungicides, which by themselves are not normally toxic to bees, can interact with other pesticides and have negative impacts on pollinator survival or pollinator health. Using any pesticide in your garden requires caution.

How do pollinators get exposed to pesticides? Pollinating insects can be exposed to pesticides in a variety of ways:

  • Direct contact with sprays or insecticidal dusts;
  • Residual insecticides left on blooming plants or weeds;
  • Systemic pesticides which are absorbed by the plant and move through the plant tissues, including pollen and nectar, upon which pollinators forage, and
  • Pollinators can drink water contaminated with insecticide.

For more information on pesticides and simple steps to protect pollinators from pesticides, click here.



Native and managed pollinators are affected by a variety of parasites and diseases that can negatively impact their health and survival. Some of these parasites and pathogens are specific to particular species, while others, such as some fungal diseases and viruses, may be more generalist in nature and shared among a variety of different pollinators. The impacts of these diseases are still poorly understood, but the scientific community is working to learn more. 

Some diseases and parasites can be accidentally propagated in the nesting sites provided by homeowners. Whether encouraging nesting sites for native pollinators or providing artificial nesting sites for bees, care must be taken to ensure that they are properly installed and maintained. Diseases and parasites that infect pollinators inside one yard may spread and negatively affect populations in surrounding yards.  Maintaining healthy bees not only protects the bees on your property, but also helps to mitigate the spread of diseases and parasites among other native pollinators.

Here are two examples of common nest site pathogens:

Moulds - A dangerous mould that commonly affects solitary bees is called chalkbrood (Ascophera aggregata and other species). This fungal disease can quickly spread among bee populations when spores from infected bees are deposited on flowers while foraging. The spores can also contaminate nesting materials.

Foliar moulds - These moulds are less serious but can still cause problems for developing bees. The mould can build up in nest material that is reused between years. More information on foliar moulds and their control in leafcutting bees can be found here.

Click here to learn more about artificial nest site maintenance and pathogen control.

healthy leafcutting bee larvae
Healthy leafcutting bee larvae
chalkbrood infected larvae with black spores
Chalkbrood infected larvae with black spores. Photo credit: David Ostermann.



A variety of tiny wasps can affect nesting bees. Parasitoid wasps lay their eggs in developing bees by using their spear-like ovipositor (a sharp tube for laying eggs) to poke through the walls of the nest cells. The egg hatches and the wasp larva consumes the immature bee as it grows, ultimately killing the bee. Parasitoid wasps, such as Chalcid wasps, are natural parasitoids of pollinators and a certain percentage of insects will always be parasitized each season. In some cases, these parasitoids can be harnessed to control agricultural pests.

Some parasitoid wasps may be more hazardous. An introduced species, Pteromalus venustus, targets both managed and native leafcutter bees. Severe infestations may have negative effects on the nests of these important pollinators. To learn more about this pest, click here.

Issues with parasitoid wasps may arise when using artificial nests at home, particularly if cardboard or staw-type liners are used. Click here to learn how to make artificial nests safer for bees.

Chalcid wasp Pteromalus venustus parasitizing leafcutting bee cell
Chalcid wasp Pteromalus venustus parasitizing a leafcutting bee cell. Photo credit: David Ostermann.


Managed pollinators, particularly honey bees, are susceptible to parasitic mites called varroa mites. Varroa mites, in combination with the viruses they transport, will eventually kill the colonies. There is evidence that when colonies with high levels of infection are in a weakened state, some of the viruses may spill over into the native bee population. The consequence of these viruses on native bee populations is still being understood.  

If managing honey bees on your property, it is important to ensure that the bees are maintained in a healthy state. Click here to learn more about honey bee health.


There are many natural predators that use pollinators as food. Birds, such as woodpeckers, and mammals, such as bears are just a couple of examples of animals that attack nest sites and consume the immature bees. Adult insects may also become food. Crab spiders and ambush bugs wait on open blooms to feed on foraging pollinators.

While getting eaten is a part of nature, predation can be a problem for nest sites at home. Bee houses can become attractive to predators and may be a target if not cared for effectively. Click here to learn how to protect artificial nests from predators.