Suomen ympäristökeskus

Number of moths has remained stable for 30 years, but the species have changed significantly


The 30th anniversary report of the national Nocturna moth monitoring, coordinated by the Finnish Environment Institute (Syke) and launched in 1993, presents the history, background and changing species of moths in Finland. Nocturna is one of Finland's longest-running monitorings of species and the third longest-running moth monitoring in Europe. As moths are sensitive to changes in the environment, their monitoring provides valuable information about the effects of global warming, for example.

Black Arches (Lymantria monacha).
Black Arches (Lymantria monacha). Helmut Diekmann

The emerging dominance of southern moth species

 During the period of the national moth monitoring, several dozen new species of moths have spread into Finland. In addition, many species that were previously scarce and confined to the south of the country have spread strongly northwards, resulting in a more "southern" composition of moth communities, especially in the southern half of the country. At the same time, many species that have adapted to the cool climate found in Finland have moved further north and even disappeared from more southerly areas.

 “Such changes are expected to continue in the future as the climate warms,” says Juha Pöyry, Senior Researcher at Syke.

Overall, the number of moth species detected annually at monitoring sites has increased over the past 30 years. Many species have also seen strong increases in numbers, but an equal number of species have declined. A strong annual variation in the total number of individuals has been observed, and throughout the monitoring period the abundance of moths has been found to fluctuate on a cycle of about 10 years.  Despite the fluctuations, there has been no clear upward or downward trend in the total number of individuals.

Relative change in the total number of individuals of moths between 1993 and 2022. Numbers of individuals have fluctuated greatly over the years, but no clear downward or upward trend has been observed. @Syke
Number of moth species observed per year in different parts of Finland. A greater number of species is shown in the maps in a darker colour. An increase in the number of species over the years is clearly visible. @Syke

Moth monitoring provides valuable information 

In addition to global warming, the most likely environmental causes of changes in moth populations include land use changes, such as logging and intensified farming, which may have degraded habitats for some species. Nitrogen deposition through food chains and reduced air pollution may also have contributed to the changes. For example, moth species that feed on lichens are likely to have benefited from the reduction in acid deposition and the increase in nitrogen content of lichens.

The effects of warming temperatures and a longer growing season are also reflected in the increasing number of moths that are multivoltine, with more and more species producing a second generation in late summer or autumn.

Living in a wide range of diverse habitats, moths react to and are sensitive to changes in their environment.

“It would be important to continue monitoring moths in the future, so that we have up-to-date information on the effects of these changes," says Ida-Maria Huikkonen, a researcher at SYKE.

Moth monitoring time series one of the longest in Europe

The Nocturna moth monitoring started in 1993 as a general survey covering a wide range of habitats, but in the late 1990s it focused mainly on monitoring moth species in forest habitats. Nocturna is one of Finland's longest-running surveys of species and the third longest-running moth survey in Europe.

Monitoring has been carried out using light traps: the traditional Jalas moth traps were initially used, but in 2020 a new type of freezer trap was introduced. Originally, the regional ELY centres were responsible for the maintenance of the traps, but nowadays this is largely done on a voluntary basis.

The accumulation of high-quality data has been made possible throughout the monitoring activities by moth enthusiasts who have acted as volunteer data analysts.

“There’s a long tradition of butterfly and moth hobbyists and research in Finland, and there have been plenty of enthusiastic moth observers over the years”, says Huikkonen.

The long, geographically comprehensive time series is extremely valuable and has been widely used in scientific studies. The data has been used to study species distributions and their links to environmental changes, such as climate change, and interactions between different groups of organisms.



Researcher Ida-Maria Huikkonen,, p. 0295 252 255

Senior Researcher Juha Pöyry,, p. 0295 251534

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