Chris van Swaay

Crazy but well worth 4 minutes of your day.

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).

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.

Veel meer natuur nodig om nuttige insecten voor de landbouw te behouden Regels van de EU die tot herstel van de insectenpopulatie moeten leiden zijn ontoereikend, blijkt uit Wagenings onderzoek dat donderdag gepubliceerd is in het wetenschappelijke tijdschrift Science.

Veel meer natuur nodig om nuttige insecten voor de landbouw te behouden

Veel meer natuur nodig om nuttige insecten voor de landbouw te behouden Regels van de EU die tot herstel van de insectenpopulatie moeten leiden zijn ontoereikend, blijkt uit Wagenings onderzoek dat donderdag gepubliceerd is in het wetenschappelijke tijdschrift Science.

www.trouw.nl/duurzaamheid...

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.

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.

Semi-natural grasslands as a nature-based solution for climate change mitigation: An assessment of carbon and plant communities across age gradients Semi-natural grasslands have the potential to sequester carbon and enhance biodiversity and therefore offer opportunities as nature-based solutions fo…

Semi-natural grasslands as a nature-based solution for climate change mitigation: An assessment of carbon and plant communities across age gradients...

www.sciencedirect.com/science/arti...

Though I wonder, because it is normally typical for C hyale to be attrackted to its host plant, C alfacariensis feeds on H comosa and Coronilla varia and probably others). They can only be seperated by DNA or by larvae (which are relatively easy to id).

It is clearly a Colias hyale/alfacariensis, which cannot be separated in the field, but C hyale does not occur (as far as I know) south of the Alps, so this must be alfacariensis.

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

Colias alfacariensis

This is a Clouded Yellow Colias croceus, another species, and a migrant from the south.

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.

No, we don’t monitor hibernators, would be interesting.

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.

Enjoy!

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.

Pity not as 15min count. Would still be in the north, comparable to Denmark, so would fit in the general picture.

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.

But remember P rapae also puts eggs on the same plant. Check your young larvae, they are different in the first two stages, with P mannii having a black head and P rapae a green head. See lepiforum.org/wiki/page/Pi... and lepiforum.org/wiki/page/Pi.... Older larvae cannot be separated.

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.

Droogte is idd vermoedelijk de oorzaak voor de slechte kwaliteit van de brandnetels. De atalanta zal het wel overleven, die proberen het volgend jaar gewoon weer opnieuw, maar de buddleia's zijn nu schrikbarend leeg.

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?

Hij is veel kleiner dan een boomblauwtje. Dat zie je natuurlijk niet op de foto, maar in het veld valt het meteen op, het is echt een klein friemeltje.