Chris van Swaay

After the extremly hot and dry summer of 2018 numbers of the Dark green fritillary (S aglaja, grote parelmoer) on Dutch Butterfly Monitoring transects crashed and has not recovered. I fear it could get extinct in NL soon, what is amazing for a species that can live in so many different habitats.

The effect of different grazing managements on butterfly abundance, diversity and composition at a calcareous upland site Research from an upland calcareous site in the Yorkshire Dales finds light cattle grazing supports 4.9× as many butterflies and 1.7× as many butterfly species as light sheep grazing, while ungrazed a...

Here is the full paper
#conservationevidence
@richardfoxbc.bsky.social @djhbutterflies.bsky.social @martinswarren.bsky.social @ukbutterflies.bsky.social @savebutterflies.bsky.social @chrisvanswaay.bsky.social @pietervantieghem.bsky.social

besjournals.onlinelibrary.wiley.com/doi/10.1002/...

Not yet, this comes from the GBI calculations by Reto. 2025 will be possible by the end of this year.

The density of the Common Blue (P icarus) per 50km square in 2024 on eBMS Butterfly monitoring transects (www.butterfly-monitoring.net) shows a W-E cline, with lowest densities in Ireland, UK, Portugal and NL and highest in Sweden, Austria, Italy and Balkans.

In 2025 the number of transects where expert volunteers count butterflies in NL rose to almost 1600. On most of them (1257) all butterflies are counted, but some transects are for one species only or plots for egg-counts.

Begin januari gaf de Rechtbank Noord-Nederland aan dat gegevens over het gebruik van pesticiden beschikbaar moeten worden gesteld aan belanghebbenden.

Om deze vereiste transparantie te traineren gaat de staatsecretaris nu in hoger beroep.
uitspraken.rechtspraak.nl/details?id=E...

Number of butterfly species per 5x5km square in Netherlands in 2025. The richest sites are on the Veluwe (centre) and South Limburg (southeast). The open polders in N Holland, Friesland, Groningen and Flevoland have the least number of species.

2025 was another bad year for the Chequered Skipper in NL. The distribution of this butterfly is getting more and more sparse. The species cannot cope very well with the dry years since 2018.

Our second Masterclass in identifying European butterflies is coming up next Wednesday 17th Feb. This one covers the trickier species in the Atlantic region given by renowned expert Chris van Swaay. The Webinar zoom link: us06web.zoom.us/j/81934375118

That's not as it's supposed to be. All issues are open on github.com/BiologicalRe..., and if you have a github account (or make one), you can add an issue yourself.

Coenonympha arcania, pearly heath Widespread in lowland Europe, often on calcareous grasslands with a mixture of shrubbery. The white postdiscal spot is large and the upper eye spot on the hindwing is on the inside of the white zone.

Coenonympha gardetta, Alpine heath Widespread on grasslands above treeline in the Alps. The white is limited and eyespots are all in line on the outer edge of the white zone.

Coenonympha (gardetta) cephalidarwiniana, Darwin's heath complex On the French southern Alpine slopes there is a population with intermediate features, nowadays known as "cephalidarwiniana", externally close to C. arcania. These populations seem to have risen from hybridisation events but are stable now, species in the making. See https://doi.org/10.1002/ece3.5220 for more information, the name "macromma" has been used there for this species, but this has recently been shown to be a mistake, see https://www.areeprotettealpimarittime.it/media/140e9804.pdf

Coenonympha (gardetta) darwiniana, Darwin's heath complex On the border regions of Switzerland & Italy, Ticino, Domodossola etc there is a populations of heaths that look a bit like Alpine heaths but are much warmer in color and where the upper eyespot is just placed a bit more to the inside of the white zone. These populations seem to have risen from hybridisation events but are stable now, species in the making. See https://doi.org/10.1002/ece3.5220 for more information. These are the true Darwin's heaths

Pearly heath & Alpine heath form a complex of seemingly integrades in the southern Alps known under the name Darwin's heath - Coenonympha (gardetta) darwiniana. Here's the 4 players in that complex, check ALT text for more info on these species in the making #darwinday #dailylepi #butterflies

For all who more or less know the butterflies of NW Europe, but find the diversity of the Balkans overwhelming, there is a masterclass on "Eastern continental and Balkan butterfly species" by Rudi Verovnik on 11th February at 15h CET. For more details see butterfly-monitoring.net/epic-butterfly

Het is alleen geen bosparelmoer

Goed idee

YouTube video by Vroege Vogels Vroege Vogels - Vlieland Vlinderland

youtu.be/DhR_JpG3wQc

The Small Heath (hooibeestje, C pamphilus) experienced a huge crash in 1991 on Dutch Butterfly Monitoring transects, maybe caused by extreme cold nights (-8C) in April. Though numbers are slowly going up, the species never fully recovered. #vlindermaand

Brown Hairstreak (sleedoornpage, Thecla betulae) is a local species in NL, and can be found in the centre of the country where sandy soils meet clay, often in urban areas, as well as in S Limburg (SE NL). This distribution has been more or less unchanged for the last 30 years. #vlindermaand

Probably

The Green-veined White (klein geaderd witje, P napi) is still widespread and common in NL, but numbers have halved since 1990 on Dutch Butterfly Monitoring transects. With the species preferring moist circumstances, the increasing number of droughts by climatechange surely have effect. #vlindermaand

#vlindermaand

The Sooty Copper (L tityrus, bruine vuurvlinder) has shown serious declines, esp. in the north of NL. Only on the Veluwe (centre) the situation is better. This species is vulnerable to N deposition (fartmann.net/downloads/ar...).

Not sure why that was not calculated, would have to check.

The Gatekeeper (P tithonus, oranje zandoogje) is doing well in de coastal dune-transects of the Dutch Butterfly Monitoring Scheme, but shows declines in the Agricultural area (where most transects are in verges) and esp. woodland. We don't know why the trend on woodland is so negative. #vlindermaand

Large and Small tortoiseshell (grote en kleine vos, N polychloros and A urticae) show opposite trends in their distribution in NL. The Large T used to be rare, and is now widespread, esp. in the eastern half. The Small T is now rare outside the W and N. #vlindermaand

As NL is at the NW-edge of the distribution of the Swallowtail (koninginnenpage, P machaon) we see periods of expansion (2009-2013 and 2018-2025) alternate with periods of retraction (2014-2017). #vlindermaand

Dat hebben wij ook eens gedaan, heel goedkoop op de 13e verdieping, daar wil geen gokker slapen.

Camouflage: Green Hairstreak - Groentje - Callophryx rubi. #vlindermaand

Probably the wet conditions, the species profits from hot and dry weather.

Around 1990 the Queen of Spain Fritillary (I lathonia, kleine parelmoer) in NL was restricted to the coastal dunes. After 2000 the inland was colonised, but not from the coast, but from the southeast (B and D). In 2024 the species crashed, some recovery in 2025. #vlindermaand