Heat can affect wild bees long after summer |
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For urban green spaces, this means that shade and cool areas are important alongside flowers
Not only drought, but especially extreme heat is becoming an increasing problem for wild bees. During heatwaves, bees fly less, food availability decreases and reproduction can be disrupted. Bee species that are already under pressure are particularly affected. This was investigated by Natuurpunt.
| The rhododendrons are dried out at 37 degrees Celsius on the university campus in Nijmegen (Image NWST for illustration) |
During a heatwave, wild bees seek shade more often to keep their body temperature under control. As a result, they make fewer flights to flowers and less pollen reaches the nest. At the same time, high temperatures and drought affect plants. Flowers can become smaller and produce less nectar and pollen.
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During a heatwave, wild bees fly less and find less food
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Heat also affects reproduction
Research shows that heat also affects reproduction. In male red mason bees that experience heat stress during development inside the cocoon, sperm production can decrease by around one third. The sperm cells are also less mobile. Females can produce fewer and smaller eggs due to heat.
Bumblebees are vulnerable as well. After mating, a queen stores sperm in her body to start a colony later. Extreme heat can permanently damage these cells. A summer heatwave can therefore affect the development of a new nest in the following spring.
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A summer heatwave can affect a bee nest in the following spring
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Above 40 degrees becomes critical
Every insect species has a temperature at which important body functions begin to fail. For bumblebees, this limit is often around 42 to 45 degrees. Bumblebees are relatively well adapted to cold conditions, but less able to cope with extreme heat. Research indicates that wild bees have only limited ability to adapt to increasingly high temperature peaks.
Bees that survive a heatwave are not always out of danger. Heat can cause lasting damage to cells and proteins. As a result, bees may still die sooner after a heatwave. They then have less time to build nests and reproduce.
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Bees that survive extreme heat can still die sooner afterwards
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More attention to cool areas in urban green spaces
For urban green space managers, the impact of heat is an additional point of attention when creating habitats for wild bees. Providing enough flowers alone is not always sufficient. Variation in planting, shade and areas that heat up less quickly can also be important during hot periods.
This is especially relevant for wild bees that are already under pressure due to habitat loss and other disturbances. According to researchers, more extreme summers add an additional risk.
This article was previously published on 20 August 2026 on the website of Stad + Groen.
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