The biomass of insects in Norway has decreased over the last four years. Weather has had an impact on insects who prefer cold and snow rich winters to thrive.
Trapping insects in Troms in Northern Norway. Photo: Vegar Seljestokken, NINA
That insects thrive in warm summers are understandable. More surprising is it that cold winters with high precipitation have a positive effect. As part of the National Monitoring Program for insects in Norway, NINA researchers have looked at the effects of winter and spring weather on insect biomass.
- In the four years we have been collecting insects, biomass has decreased. Hopefully the trend is short-term and that it will reverse with more favourable weather conditions. At the same time, we fear climate change may have negative effects on insects in the future, says NINA researcher and project manager Jens Åström.
The researchers have looked at how precipitation and temperature affect the biomass of insects collected in traps in forests and meadows across large parts of the country. Biomass is calculated as the weight of insects a standardized trap collects per day. Warm and not too dry weather in summer has a positive effect, while a dry and mild winter creates challenges.
Snow as insulation
- It is challenging for insects to survive the winter in Norway, but a thick snow cover insulates well. Based on this, we assume that higher temperatures, which naturally will result in less snow, will affect insects, explains Åström.
In the same way, an early spring will cause insects to become active "too early". Precipitation in the form of rain or setbacks to more wintry conditions can then affect survival.
Cold winters rich in precipitation are positive for insects. Here two Boreus westwoodi mating on snow. Photo: Arnstein Staverløkk, NINA
So far, the National Monitoring Program for insects in Norway has estimated an approximate 14 % decrease in insect biomass annually in the period 2020-23.
For the program, it is reassuring that we are able to detect time trends, but we naturally hope that the decline is short-term, says Åström.
Insects working for nature and people
Insects play a crucial role in most ecosystems. They break down plant material so that nutrients can be used again, they pollinate plants, help regulate pest populations, and they are food for other animals. Several studies show, however, that insect populations have been greatly reduced in recent years, particularly in Europe.
The consequences are difficult to predict in detail, but entire ecosystems could potentially be affected. It is therefore important to understand what influences the occurrence of insects, for example land use or changes in climate. To be able to do that in Norway, continous long-term and country-wide monitoring is crucial, says Åström.
The Chrysops relictus is one of the species commonly seen in the researchers' traps. Photo: Arnstein Staverløkk, NINA
Monitoring becomes country-wide
In 2023, the area covered by the Monitoring Program was extended to also include Northern Norway, which involves a large expansion of weather conditions and latitudes covered by the Program. In 2024, Western Norway will also be included, making the monitoring of meadows nationwide. Forests are currently only monitored in Eastern Norway. The Monitoring Program is run by NINA and financed by the Norwegian Environment Agency.
Contact Jens Åström
Read the report Monitoring of insects in Norway. Report from the 2023 field season