Chris van Swaay
@chrisvanswaay.bsky.social
Ecologist and butterfly expert at Vlinderstichting and Butterfly Conservation Europe
Northern Chequered Skipper (C silvicola, geelbont dikkopje): Vulnerable (A2b) in EU (www.bc-europe.eu/webpage.php?...) because of population declines on European Butterfly Monitoring transects in eBMS (www.butterfly-monitoring.net).
October 22, 2025 at 6:22 AM
Northern Chequered Skipper (C silvicola, geelbont dikkopje): Vulnerable (A2b) in EU (www.bc-europe.eu/webpage.php?...) because of population declines on European Butterfly Monitoring transects in eBMS (www.butterfly-monitoring.net).
Now the 2025 field season for butterflies has come to an end, it is a good moment to look back at the great work of the recorders of Dutch Butterfly Monitoring transects. Almost 400,000 butterflies counted in 2025 on 1372 locations, 8,5 million since 1990 on 212,327 km. Thanks for all hard work!
October 6, 2025 at 11:09 AM
Now the 2025 field season for butterflies has come to an end, it is a good moment to look back at the great work of the recorders of Dutch Butterfly Monitoring transects. Almost 400,000 butterflies counted in 2025 on 1372 locations, 8,5 million since 1990 on 212,327 km. Thanks for all hard work!
2025 will mark another bad year for the Dark Green Frit (grote parelmoer, S aglaja) with numbers comparable to 2023 and 2024 in NL (=low). Once widespread throughout the country, and numbers ten years ago still good, now reasonable numbers only on Vlieland and N-Texel (the islands in the NW).
October 1, 2025 at 6:00 AM
2025 will mark another bad year for the Dark Green Frit (grote parelmoer, S aglaja) with numbers comparable to 2023 and 2024 in NL (=low). Once widespread throughout the country, and numbers ten years ago still good, now reasonable numbers only on Vlieland and N-Texel (the islands in the NW).
2025 marks a very bad year for the Glanville Frit (veldparelmoer, M cinxia) in NL. Only the coastal population had >10 butterflies, on the inland ones the species almost vanished. Poor weather in 2024 made few larvae enter last winter.
September 30, 2025 at 7:17 AM
2025 marks a very bad year for the Glanville Frit (veldparelmoer, M cinxia) in NL. Only the coastal population had >10 butterflies, on the inland ones the species almost vanished. Poor weather in 2024 made few larvae enter last winter.
The Painted Lady (distelvlinder, V cardui) was only seen in low numbers on Dutch Butterfly Monitoring transects this year. It is a migrant species, and the graphs show that 1996, 2003, 2009 and 2019 had large invasions, the other years just a few managed their way to NL.
September 29, 2025 at 9:32 AM
The Painted Lady (distelvlinder, V cardui) was only seen in low numbers on Dutch Butterfly Monitoring transects this year. It is a migrant species, and the graphs show that 1996, 2003, 2009 and 2019 had large invasions, the other years just a few managed their way to NL.
The Swallowtail (koninginnenpage, P machaon) had a good year on Dutch Butterfly Monitoring transects, clearly better than 2024 (though we have had better years). Exceptional was the large 3rd generation, which is usually small in NL.
September 16, 2025 at 6:25 AM
The Swallowtail (koninginnenpage, P machaon) had a good year on Dutch Butterfly Monitoring transects, clearly better than 2024 (though we have had better years). Exceptional was the large 3rd generation, which is usually small in NL.
The addition of flexcounts, as eg 15min counts, to Dutch Butterfly Monitoring transects, makes it possible to produce detailed flight curves. Although 2025 was warmer, the White Admiral (kleine ijsvogel, L camilla) had an earlier start in 2024. Also watch the small 2nd gen.
September 10, 2025 at 11:43 AM
The addition of flexcounts, as eg 15min counts, to Dutch Butterfly Monitoring transects, makes it possible to produce detailed flight curves. Although 2025 was warmer, the White Admiral (kleine ijsvogel, L camilla) had an earlier start in 2024. Also watch the small 2nd gen.
An interesting pattern for the abundance of the Common Blue (icarusblauwtje, P icarus) on Dutch Butterfly Monitoring transects: a large and early 1st gen, followed by a smaller 2nd gen (which is normally larger than the 1st gen) and a small 3rd gen right now. Food quality in summer has been poor.
September 8, 2025 at 9:26 AM
An interesting pattern for the abundance of the Common Blue (icarusblauwtje, P icarus) on Dutch Butterfly Monitoring transects: a large and early 1st gen, followed by a smaller 2nd gen (which is normally larger than the 1st gen) and a small 3rd gen right now. Food quality in summer has been poor.
The Hummingbird hawk-moth (kolibrievlinder, Macroglossum stellatarum) is a climate opportunist from the south, and they love warm weather. Numbers on Dutch Butterfly Monitoring transects were high this summer, and the next generation just started. So watch out for these 'hummingbirds' in your garden
September 4, 2025 at 8:14 AM
The Hummingbird hawk-moth (kolibrievlinder, Macroglossum stellatarum) is a climate opportunist from the south, and they love warm weather. Numbers on Dutch Butterfly Monitoring transects were high this summer, and the next generation just started. So watch out for these 'hummingbirds' in your garden
It's been a while since we had a good migration year for the Pale Clouded Yellow (gele luzernevlinder, C hyale) on Dutch Butterfly Monitoring transects, but finally numbers are comparable to 1992, 2003, 2006 and 2017. The species declined in C Europe, the origin of our butterflies.
September 2, 2025 at 6:31 AM
It's been a while since we had a good migration year for the Pale Clouded Yellow (gele luzernevlinder, C hyale) on Dutch Butterfly Monitoring transects, but finally numbers are comparable to 1992, 2003, 2006 and 2017. The species declined in C Europe, the origin of our butterflies.
After a great start this spring the Peacock (dagpauwoog, A io) had a poor 1st gen in July, and the 2nd gen is more or less absent on Dutch Butterfly Monitoring transects. Numbers are now much lower than in 2024.
September 1, 2025 at 2:07 PM
After a great start this spring the Peacock (dagpauwoog, A io) had a poor 1st gen in July, and the 2nd gen is more or less absent on Dutch Butterfly Monitoring transects. Numbers are now much lower than in 2024.
Yesterday I bumped into this fresh male Sooty Copper (bruine vuurvlinder, L tityrus), of what will probably become a 3rd gen. Also a new site for me on S Veluwe. This species shows a large decline, esp. in the north of NL, since I started butterflying.
August 31, 2025 at 9:38 AM
Yesterday I bumped into this fresh male Sooty Copper (bruine vuurvlinder, L tityrus), of what will probably become a 3rd gen. Also a new site for me on S Veluwe. This species shows a large decline, esp. in the north of NL, since I started butterflying.
Not that long ago in August Buddleia's could be covered with Small Tortoiseshells (A urticae, kleine vos). On eBMS transects and 15min counts (www.butterfly-monitoring.net) this butterfly is now restricted to higher elevations or latitudes. Open squares=counted in that period.
August 26, 2025 at 11:45 AM
Not that long ago in August Buddleia's could be covered with Small Tortoiseshells (A urticae, kleine vos). On eBMS transects and 15min counts (www.butterfly-monitoring.net) this butterfly is now restricted to higher elevations or latitudes. Open squares=counted in that period.
An update of the Pieris-whites on Dutch Butterfly Monitoring transects show they all have a relatively poor 3rd gen this year. The reason recorders feel they 'only count Whites' is because all other species are doing even worse, maybe except for C hyale and C argiades in the SE.
August 25, 2025 at 9:10 AM
An update of the Pieris-whites on Dutch Butterfly Monitoring transects show they all have a relatively poor 3rd gen this year. The reason recorders feel they 'only count Whites' is because all other species are doing even worse, maybe except for C hyale and C argiades in the SE.
Clouded and Pale Clouded Yellow (C hyale+crocea, gele en oranje luzernevlinder) are migrants in NL and show large year-year fluctuations in density on Dutch Butterfly Monitoring transects. Before 1980 C hyale was considered more abundant, now it is C croceus. Numbers for 2025 up to now.
August 24, 2025 at 8:38 AM
Clouded and Pale Clouded Yellow (C hyale+crocea, gele en oranje luzernevlinder) are migrants in NL and show large year-year fluctuations in density on Dutch Butterfly Monitoring transects. Before 1980 C hyale was considered more abundant, now it is C croceus. Numbers for 2025 up to now.
Up to July numbers of Red Admiral (Vanessa atalanta) were good on Dutch Butterfly Monitoring transects, but since then they plumeted and now mid-August we have a negative record, as never before there were so few of them counted. This is most probably linked to poor nettle quality.
August 18, 2025 at 8:35 AM
Up to July numbers of Red Admiral (Vanessa atalanta) were good on Dutch Butterfly Monitoring transects, but since then they plumeted and now mid-August we have a negative record, as never before there were so few of them counted. This is most probably linked to poor nettle quality.
We had a large 1st gen of the Common Blue (P icarus, icarusblauwtje) on Dutch Butterfly Monitoring transects. But where the 2nd gen is usually twice as big, in 2025 it was even smaller, probably because of poor foodplant quality as a result of dry conditions in spring. Will we have a 3rd gen?
August 13, 2025 at 6:15 AM
We had a large 1st gen of the Common Blue (P icarus, icarusblauwtje) on Dutch Butterfly Monitoring transects. But where the 2nd gen is usually twice as big, in 2025 it was even smaller, probably because of poor foodplant quality as a result of dry conditions in spring. Will we have a 3rd gen?
As a true climate opportunist the Short-tailed Blue (C argiades, staartblauwtje), which arrived in NL in 2009, profits from hot and dry summers caused by climate change. Numbers on Dutch Butterfly Monitoring transects now higher than ever.
August 12, 2025 at 6:21 AM
As a true climate opportunist the Short-tailed Blue (C argiades, staartblauwtje), which arrived in NL in 2009, profits from hot and dry summers caused by climate change. Numbers on Dutch Butterfly Monitoring transects now higher than ever.
The mean number of butterflies on Dutch Butterfly Monitoring transects is now very low as compared to other years since 1990 (though 2024 was worse). With such low numbers flowers in gardens also stay empty: there are simply no butterflies around to visit them.
August 11, 2025 at 8:17 AM
The mean number of butterflies on Dutch Butterfly Monitoring transects is now very low as compared to other years since 1990 (though 2024 was worse). With such low numbers flowers in gardens also stay empty: there are simply no butterflies around to visit them.
iNaturalist had one in Berlin last year
August 10, 2025 at 9:38 AM
iNaturalist had one in Berlin last year
The next generation of Southern Small White (P mannii) has started, I just made this photo in the garden. You notice them as they are a bit smaller than Small Whites and have a slightly different way of flying. This generation should have a large and dark square middle spot (as on the photo).
August 10, 2025 at 9:25 AM
The next generation of Southern Small White (P mannii) has started, I just made this photo in the garden. You notice them as they are a bit smaller than Small Whites and have a slightly different way of flying. This generation should have a large and dark square middle spot (as on the photo).
The White-letter hairstreak (S w-album, Iepenpage) was always very rare in NL, but is now widely distributed over N and C NL. This is partly as we now know how to spot the species, but also true expansion.
August 7, 2025 at 3:36 PM
The White-letter hairstreak (S w-album, Iepenpage) was always very rare in NL, but is now widely distributed over N and C NL. This is partly as we now know how to spot the species, but also true expansion.
2025 so far is a good year for the Southern Small White (P mannii, scheefbloemwitje) on Dutch Butterfly Monitoring transects. With the next generation just starting we hope numbers will peak in September.
August 5, 2025 at 9:31 AM
2025 so far is a good year for the Southern Small White (P mannii, scheefbloemwitje) on Dutch Butterfly Monitoring transects. With the next generation just starting we hope numbers will peak in September.
When I started butterflying the Speckled wood (P aegeria, bont zandoogje) was restricted to woodlands in a few regions in NL, now it can be found all over the country. 2025 seems to become a good year on Dutch Butterfly Monitoring transects.
August 3, 2025 at 6:42 AM
When I started butterflying the Speckled wood (P aegeria, bont zandoogje) was restricted to woodlands in a few regions in NL, now it can be found all over the country. 2025 seems to become a good year on Dutch Butterfly Monitoring transects.
When I started butterflying in the 1980s you could see hundreds or thousands of Graylings (heivlinder, H semele) on dry heathlands in August. It could be extremely abundant. But since then numbers went down and 2025 looks like a new low on Dutch Butterfly Monitoring transects.
August 2, 2025 at 11:25 AM
When I started butterflying in the 1980s you could see hundreds or thousands of Graylings (heivlinder, H semele) on dry heathlands in August. It could be extremely abundant. But since then numbers went down and 2025 looks like a new low on Dutch Butterfly Monitoring transects.