2020 was a relatively good year for butterflies but some worrying trends continuing
Butterfly populations in Ireland generally had a good season in 2020. The multi-species butterfly index which tracks the populations of our 15 commonest species shows that the populations continue to grow from the lows of 2016, but that overall there are still -0.9% fewer butterflies than 2008, the base year of the scheme.
The good news is that populations of Small Tortoiseshell increased significantly in 2020, moving from a stable population to one showing a +6% increase on 2008. This was due to the fine weather early in the year resulting in a very large second generation in late summer. Four other butterfly species, Peacock, Brimstone, Dingy Skipper and Holly Blue experienced an increase in 2020, with that of the Peacock continuing its strong increase in population of +185% on 2008 levels.
Small Heath and Small Copper continue to decline but the rate of decline lessened last year. Nevertheless, Small Heath a butterfly of unimproved grassland with sparse fine grasses is still experiencing a strong population decline of -51%. Green-veined White population have continued to decline and are now showing a loss of -43% since 2008 and Speckled Wood have declined by -12%.
Two of our migratory butterfly species, the Red Admiral and Painted Lady experienced different fortunes in 2020. Red Admiral populations continued to increase and are now +60% more abundant than they were in 2008. In contrast, after the massive increase in Painted Lady numbers in 2019, there were fewer Painted Lady seen last year than any of the previous 12 years of the monitoring scheme. The numbers of migratory species by their nature fluctuate from year to year, yet the remarkable change in the number of Painted Lady is quite dramatic.
Established in 2008, the Irish Butterfly Monitoring Scheme has been tracking change in butterfly populations for 13 years. The scheme was established because butterflies are sensitive to changes in their environment making them good indicators of land-use and climate change. It is the longest running insect monitoring scheme in Ireland and managed by the National Biodiversity Data Centre. It involves volunteers walking a fixed route (transect) each week when weather conditions are favourable counting all the butterflies seen. It is a huge voluntary effort by citizen scientists, with 97 transects walked by 73 volunteers counting 26,547 individual butterflies. Unfortunately there are not sufficient sites monitored of our rarer or localised species to enable their populations to be tracked.
Read the detailed analysis here Irish Butterfly Monitoring Newsletter 2021