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Chris van Swaay @chrisvanswaay.eurosky.social · 11h

Next year, I will be co-leading at least one tour for butterflies. Departure is already guaranteed, but you can still join if you want to explore the Pyrenees with me: www.mariposanature.com/tours/butter.... I will post on the other tour when I have more info.

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Chris van Swaay @chrisvanswaay.eurosky.social · 11/10/2026

Max count per 1000m of Queen of Spain Frit (kleine parelmoer, I lathonia) on Dutch Butterfly Monitoring transects in 2026. Open dot=visited. Traditional high numbers in coastal dunes, but this year also lots in C and S NL. Also many near Wageningen.

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Chris van Swaay @chrisvanswaay.eurosky.social · 05/10/2026

At the end of the butterfly season the Pale Clouded Yellow larvae (gele luzerne, C hyale) will try to hibernate, the September generation was the last. The Clouded Yellows (oranje luzerne, C croceus) can't go into diapause and will either fly south or die with the first really cold night.

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Chris van Swaay @chrisvanswaay.eurosky.social · 03/10/2026

This morning in our moth-trap, Griposia aprilina, in English Merveille du jour (!), in Dutch Diana-uil. We had one last year too. I know it is not that rare, but a spectacular and beautiful moth it is. Would it be living in our oak?

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Chris van Swaay @chrisvanswaay.eurosky.social · 29/09/2026

This comma (gehakkelde aurelia, P c-album) looks like a little dragon with a small c. Both 1st (July) and 2nd generation (>July) on Dutch Butterfly Monitoring transects have moved forward in time, the 2nd gen most, but that also got much smaller over time. Does hot 2026 even produce a 3rd gen now?

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Chris van Swaay @chrisvanswaay.eurosky.social · 28/09/2026

The Essex Skipper (zwartsprietdikkopje, T lineola) had declined by >90% on Dutch Butterfly Monitoring transects since 1995. In N America the species is an invasive, accidentilly introduced around 1910, still expanding. This photo from www.inaturalist.org/observations/231653174 shows it in NW Canada.

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Chris van Swaay @chrisvanswaay.eurosky.social · 25/09/2026

Another poor year for the Purple Hairstreak (eikenpage, F quercus) on Dutch Butterfly Monitoring transects. The species spends most of the time in the canopy of oak trees, and can be hard to find, which makes them difficult to monitor. In some years, as e.g. 2018, they descend in large numbers.

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Chris van Swaay @chrisvanswaay.eurosky.social · 21/09/2026

2026 gave us more butterflies on Dutch Butterfly Monitoring transects than 2023 and 2024 (these years were the worst since 1990), and a little bit more than 2025, especially in August. But beware of shifting baseline, numbers in most years in the 1990s were often twice as high as nowadays.

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Chris van Swaay @chrisvanswaay.eurosky.social · 19/09/2026

Also moving fast along the Rhine in Germany, lots of habitat along the river. They might be here earlier : -)

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Chris van Swaay @chrisvanswaay.eurosky.social · 19/09/2026

The Lesser Purple Emperor (kleine weerschijnvlinder, Apatura ilia) has been expanding north at a speed of ±10km per year and has now started to colonise SE of NL. If this speed continues it might reach me in Wageningen in ten years or so. The expansion is caused by climate warming.

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Chris van Swaay @chrisvanswaay.eurosky.social · 09/09/2026

Distribution and trend of Dark Green Fritillary (grote parelmoer, S aglaja) in NL in 2026. It is painful to see how rare this species has now become, where it used to occur on semi-natural grasslands, woodlands, heathlands, coastal dunes, almost everywhere.

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Chris van Swaay @chrisvanswaay.eurosky.social · 08/09/2026

Migrant butterflies are having a good year on Dutch Butterfly Monitoring transects, with high numbers of Red Admiral and Painted Lady in summer, and lots of Pale Clouded Yellow now (the best year since the start of monitoring in 1990). Clouded Yellow is having an average year.

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Chris van Swaay @chrisvanswaay.eurosky.social · 02/09/2026

Since it recolonised NL in 2009, the spread north of the Mallow Skipper (kaasjeskruiddikkopje, C alceae) in the SW has been much faster than in the SE, despite having to cross stretches of water up to 5km regularly. The species prefers the clay-soils in SW and West NL and seems to avoid sandy soil.

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Chris van Swaay @chrisvanswaay.eurosky.social · 27/08/2026

Strange indeed, and very different from the >50% decline we have in NL since 1990. And this includes newcomers which the UK has much less of (as C argiades, B daphne, C alcaea e.o.).

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Chris van Swaay @chrisvanswaay.eurosky.social · 26/08/2026

The Pale Clouded Yellow (gele luzerne, C hyale) is having a good year on Dutch Butterfly Monitoring transects. In NL this is a migratory species, usually arriving from the east, now in its 3rd gen. Numbers this year so far resemble earlier top-years 2003, 2006 and 2025.

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Chris van Swaay @chrisvanswaay.eurosky.social · 20/08/2026

After a good 1st generation the Speckled Wood (bont zandoogje, P aegeria) suffers from the drought on Dutch Butterfly Monitoring transects. Numbers this summer are much lower. Still it remains a common and widespread butterfly who will recover once conditions become favourable.

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Chris van Swaay @chrisvanswaay.eurosky.social · 18/08/2026

Density of Ringlet (koevinkje, A hyperantus) per 1000m per 50km square in July 2026 on transects and 15min counts entered with the ButterflyCount app. Highest densities in Baltic, Poland, Czech Rpb and Denmark. A species sensitive to droughts, so numbers next year may be considerably lower.

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Chris van Swaay @chrisvanswaay.eurosky.social · 16/08/2026

Climate change has winners and (more) losers on Dutch Butterfly Monitoring transects, and the Grayling is one of the losers. So far 2026 shows even less butterflies than 2025. Although the species is typical for dry habitats, this used to be in an Atlantic wet climate, which has gone.

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Chris van Swaay @chrisvanswaay.eurosky.social · 30/07/2026

Lots of Scarce Coppers (morgenrood, Lycaena virgaureae) during today's walk in N Spain

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Chris van Swaay @chrisvanswaay.eurosky.social · 28/07/2026

European wildcat (Felis silvestris) in N Spain, so far we saw at least one each day on mown haymeadows.

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Chris van Swaay @chrisvanswaay.eurosky.social · 28/07/2026

Two newcomers in NL can cope very well with heatwaves as we have this year on Dutch Butterfly Monitoring transects and both have started their large 3rd generation very quickly after the large 2nd. The Short-tailed Blue colonised NL in 2009, the SSW in 2015.

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Chris van Swaay @chrisvanswaay.eurosky.social · 19/07/2026

Kleine parelmoervlinder vandaag op de vlinderstruik in onze voortuin. Een nieuwe tuinsoort voor ons. Queen-of-Spain Fritillary today on the buddleia in our front garden in the centre of NL. A new garden-species.

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Chris van Swaay @chrisvanswaay.eurosky.social · 19/07/2026

The last few weeks we have seen high numbers of Queen of Spain Frit. (kleine parelmoer, I lathonia) on Dutch Butterfly Monitoring transects. The map shows densities per 1000m from 1-18 July. Highest numbers are locally in the coastal dunes and on extensive used fields and new nature in C and S NL.

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Chris van Swaay @chrisvanswaay.eurosky.social · 17/07/2026

The Hummingbird hawk-moth (kolibrievlinder, M stellatarum) has a good year on Dutch Butterfly Monitoring transects, where day-active moths are also counted. The Six-spot Burnet had its peak much earlier than usual, the Mother Shipton (mi-vlinder, C mi) interestingly was later than usual.

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Chris van Swaay @chrisvanswaay.eurosky.social · 13/07/2026

Where the Red Admiral (V atalanta) has a good year on Dutch Butterfly Monitoring transects, Peacock (dagpauwoog, A io) and Comma (gehakkelde aurelia, P c-album) are only doing so-so. The Small tortoiseshell (kleine vos, A urticae) has been down for the last ten years.

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Chris van Swaay @chrisvanswaay.eurosky.social · 12/07/2026

Just like the Queen of Spain Fritillary (kleine parelmoer, I lathonia) the Swallowtail (koninginnenpage, P machaon) loves hot weather. I found a few in every 15min count I did today in my region in South Veluwe (NL).

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Chris van Swaay @chrisvanswaay.eurosky.social · 11/07/2026

Big numbers of Queen of Spain Fritillary (kleine parelmoer, Issoria lathonia) in my region on South Veluwe. Veel kleine parelmoers vandaag op de Zuid Veluwe.

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Chris van Swaay @chrisvanswaay.eurosky.social · 09/07/2026

A very early Brown hairstreak (Thecla betulae, sleedoornpage) on our transect in the Wageningen Rhine-floodplains. Een heel vroege sleedoornpage op ons transect in the uiterwaarden bij Wageningen.

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Chris van Swaay @chrisvanswaay.eurosky.social · 05/07/2026

In the past the Marbled White (dambordje, M galathea) did several colonisation attempts in NL, but so far all failed and the species never managed to survive 10 years on its own. Vagrants are seen every year, but this year numbers on two sites are much larger. Lets see if this new attempt succeeds.

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Chris van Swaay @chrisvanswaay.eurosky.social · 05/07/2026

Of course it can be different locally, but in NL as a whole it was fairly normal.

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Chris van Swaay @chrisvanswaay.eurosky.social · 05/07/2026

Mean number of butterflies per 1000m on Dutch Butterfly Monitoring transects per habitat last week. The high number on heathland comes from Silver-studded Blue (heideblauwtje, P argus), which can be very abundant. Overall Meadow Brown (bruin zandoogje, M jurtina) was the most abundant species.

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Chris van Swaay @chrisvanswaay.eurosky.social · 29/06/2026

The Pieris-whites have a good year on Dutch Butterfly Monitoring transects, esp. Large White (photo), Small White and Southern Small White have higher than average numbers at the end of June. The combination of enough rain a few weeks ago and Sunshine benefits these widespread butterflies.

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Chris van Swaay @chrisvanswaay.eurosky.social · 26/06/2026

Good numbers of Red Admirals (V atalanta) on Dutch Butterfly Monitoring transects. The combination of enough rain in spring and hot weather now is clearly positive for this nettle feeder.

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Chris van Swaay @chrisvanswaay.eurosky.social · 25/06/2026

Nederland heeft serieuze opgaven voor art. 10 (bestuivers) en 11 (graslandvlinderindex) van de Natuurherstelverording. Een belangrijke stap daarin zou natuurvriendelijk beheer van bermen zijn (zie www.groeneruimte.nl/nieuws/274011/?b=260624), als bv. kleurkeur (vlinderstichting.nl/kleurkeur).

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Chris van Swaay @chrisvanswaay.eurosky.social · 24/06/2026

On the Dutch Butterfly Monitoring transects we see a new wave of Painted Ladies (distelvlinder, V cardui) coming in from the south, probably with the hot air from France. This graph compares the mean number per week per 1000m with the top migration years 1996, 2003, 2009 and 2019.

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Chris van Swaay @chrisvanswaay.eurosky.social · 23/06/2026

Second generation of Map (landkaartje, Araschnia levana) is just starting at Dutch Butterfly Monitoring transect. On one or our transects we just spotted 4 fresh ones, this one actually has a lot of orange, as is more usual in the 3rd generation.

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Chris van Swaay @chrisvanswaay.eurosky.social · 16/06/2026

Poor numbers of Peacock (Aglais io, dagpauwoog) this spring on Dutch Butterfly Monitoring transects. We are at the onset of the first generation, though you can still find caterpillars. We hope for good numbers.

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Chris van Swaay @chrisvanswaay.eurosky.social · 06/06/2026

Occupancy-trend of the Chequered Skipper (bont dikkopje, C palaemon) in NL. After a long period of gradual decline distribution in 2024 and 2025 fell by almost 50%, esp. small populations were abandoned. Helas 2026 showed little recovery as far as we can tell now.

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Chris van Swaay @chrisvanswaay.eurosky.social · 02/06/2026

With numbers of Painted Ladies (distelvlinder, V cardui) rising on Dutch Butterfly Monitoring transects, it's a good moment to put this invasion in perspective. The graph shows a small influx, comparable with 1996 and 2003, and smaller than 2009 and 2019. But lets see how it continues.

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Chris van Swaay @chrisvanswaay.eurosky.social · 27/05/2026

Hornet moth (Sesia apiformis) in Wageningen floodplains (NL). We see them every year, but still fun. Hoornaarvlinder (Sesia apiformis) in Wageningse uiterwaarden. We zien ze elk jaar, maar het blijft leuk.

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Chris van Swaay @chrisvanswaay.eurosky.social · 22/05/2026

As May progresses we slowly sink into a few weeks with low numbers of butterflies in NL. We used to call this the June-dip, but more and more of it occurs in May as a result of climate warming. Spring butterflies are almost gone, and summer butterflies start emerging around mid June.

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Chris van Swaay @chrisvanswaay.eurosky.social · 14/05/2026

Het boomblauwtje wordt vaak gemeld uit stad en dorp, maar de transecten van het NEM meetnet dagvlinders laten zien dat de hoogste dichtheid op heide wordt gevonden, waar struikhei een belangrijke waardplant voor de rups is.

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Chris van Swaay @chrisvanswaay.eurosky.social · 14/05/2026

Although the Holly Blue (boomblauwtje, C argiolus) is often seen in gardens, on Dutch Butterfly Monitoring transects by far the highest density is counted on heathland, where Common Heather (Calluna vulgaris) is an important foodplant.

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Chris van Swaay @chrisvanswaay.eurosky.social · 11/05/2026

This year sees an early arrival of Painted Ladies (distevlinder, V cardui) on Dutch Butterfly Monitoring transects. These butterflies come from the Mediterranean and migrated north through France. In some years the can be very abundant (eg 2009 and 2019), in other years almost missing.

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Chris van Swaay @chrisvanswaay.eurosky.social · 05/05/2026

A very poor spring generation of the Map (Landkaartje, A levana) on Dutch Butterfly Monitoring transects. Numbers are much lower than in 2025, but also lower than in most of 1990-2025. Low quality nettles because of the dry spring of 2025 caused a poor 3rd gen and low numbers now.

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Chris van Swaay @chrisvanswaay.eurosky.social · 28/04/2026

A relatively good year for the Orange Tip (oranjetipje, A cardamines) on Dutch Butterfly Monitoring transects. Last week we crossed the peak level and numers are going down again. The graphs also shows we have to start the season before 1 April or we miss part of the flight period.

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Chris van Swaay @chrisvanswaay.eurosky.social · 24/04/2026

Where the distribution (=occupancy) of the Large white (groot koolwitje, P brassicae) is stable, it occurs everywhere, the population level is now significantly lower on Dutch Butterfly Monitoring transects, in spite of strong fluctuations. After 2008 the pop index never was >100.

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Chris van Swaay @chrisvanswaay.eurosky.social · 18/04/2026

Low numbers of Peacock (dagpauwoog, A io) on Dutch Butterfly Monitoring transects this year, after last years poor summer generation and missing 2nd gen because of poor quality nettles. This spring is also dry and much too warm so far, so things don't look good for nettles and peacocks this year.

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Chris van Swaay @chrisvanswaay.eurosky.social · 15/04/2026

Numbers of Chequered Skipper (bont dikkopje, C palaemon) can fluctuate a lot, but the last few years have been bad for the species with a decline of 70% since 1990. Also distribution (=occupancy) declined with 30%. As a species of moist woodland it has a problem with dry summers.

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Chris van Swaay @chrisvanswaay.eurosky.social · 14/04/2026

Density of Brimstone (citroenvlinder, G rhamni) on Dutch Butterfly Monitoring transects this spring higher than in spring 2025, but also higher than in summer 2025 (and these are the same butterflies as they hibernate as adult). They probably hibernated (or aestivated) quickly after emerging.

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