Pollinators surge this summer, but long-term decline remains unclear

Day-flying butterflies increased by 43 per cent and bumblebees by 69 per cent this summer compared with last year, Yle reports. Researchers say favourable weather was behind the rise, but there is not enough long-term data to assess the overall decline in pollinator species.

Butterflies and bumblebees were particularly abundant in the garden of Marja Nuora and Erkki Pöytäniemi in Karjalohja, where the couple volunteer to monitor pollinators.

Data compiled by the Finnish Environment Institute shows that day-flying butterflies performed better than they have in several years. Most pollinator species also increased in number.

The summer began with record dryness, but rain and warm periods followed from the end of May onwards.

“The summer has been suitably warm and wet. After the dry spring, it has been a very good summer,” said Janne Heliölä, a researcher at the Finnish Environment Institute who coordinates volunteer pollinator monitoring.

Species that fly in the middle and latter parts of summer did particularly well. Small tortoiseshell and peacock butterflies were abundant after a two-year break.

Volunteers collect the data

The monitoring programme relies on observations by volunteers. Just under 50 people monitor day-flying butterflies and slightly more than 50 monitor bumblebees in different parts of Finland.

“The unpaid work of citizens makes this possible. The Finnish Species Information Centre only coordinates the work and reports the results,” Heliölä said.

Nuora has monitored bumblebees in Karjalohja since 2019. Her work involves regularly walking a two-kilometre route and recording the species she sees.

She said she joined the programme to build a closer connection with nature. Pöytäniemi began monitoring butterflies this summer and recorded between 40 and 50 species in total, with as many as 20 species seen on a single survey.

One summer does not show the long-term trend

Pollinators in Finland appear to be in a more stable position than those elsewhere in Europe, although the available information is limited.

There has been no clear change in the abundance of moth species over a time series of more than 20 years. Among day-flying butterflies, slightly more species have declined than increased.

Bumblebees have been monitored for only six years, making it too early to identify a long-term trend.

There is no long-term monitoring data on the numbers of wild bumblebees and bees in Finland. More pollinator species are classified as threatened, although that development may also reflect improved data collection.

Heliölä said the summer appeared to mark a recovery, but warned that pollinator populations fluctuate considerably.

“We need a time series of about 20 years before we can draw conclusions about whether the trend is upwards or downwards,” he said.