Wednesday, 18 March 2015

Some pitfalls in the recognition of Large and Scarce tortoiseshell

During the last week I have been searching again for Scarce tortoiseshell Nymphalis xanthomelas in the northern part of Belgium. Unfortunately without luck for the Scarce tortoiseshell but I still had a species-rich two days with eggs of Ilex hairstreak Satyrium ilicis, caterpillars of Glanville fritillary Melitaea cinxia and a Large tortoiseshell Nymphalis polychloros, in fact pretty scarce in the north of Belgium...

Ilex hairstreak egg, 12th of March

Large tortoiseshell, 12th of March

Glanville fritillary caterpillars, 17th of March

In the meantime a second Scarce tortoiseshell for this year has been seen in Belgium, a typical individual. In the Netherlands at least 17 have already been seen this spring! While looking at pictures of both large and scarce tortoiseshell I noticed that determination is not always straightforward. Some individuals can give rise to doubts, even with good photographs. I give three examples with a little analysis.

Example one: difficult Large tortoiseshell

This is a Large tortoiseshell with a rather broad dark edge to the hind wing, especially on the left side. The dark edge is still a bit wavy but much less than compared to the one I saw last week. The dark band is still edged off with a little yellowish but almost unnoticeable. Also the basal spot is rather divided in two. Notice also the dark edge to the front wing, close to the apex it gets a bit slimmer, especially in the curve just before the apex whereas in Scarce tortoiseshell in most cases the band stays evenly broad. You can just see a dark front leg.
The details of this picture (photographer, location, date,...) can be found here:

Example two: difficult Scarce tortoiseshell

The dark edge to the hind wing is very narrow and pretty wavy whereas in almost all Scarce tortoiseshells this band is (evenly) broad. There is however no sign of a yellowish edge to the dark band, in fact yellowish tones lack almost completely from the hind wing giving a more reddish appearance, the name "xanthomelas" literally means "red (xantho) - black (melas)" in contrast to "polychloros" (lots of colors). Also notice the dark edge on the front wing even getting broader in the curve near the apex. You can also spot the pale legs. Note also the more "extreme" shape of the wings compared to previous individual, reminding a little of a Comma Polygonia c-album. Details of this picture can be found here:

Example three: difficult Large tortoiseshell

This individual really seems to have pale legs... There are however some remarks. First of all, this individual was photographed more than a week before the invasion started in the north of the Netherlands and on the location with probably the highest density of Large tortoiseshells in Belgium in the south of the country. Also the wing shape looks typical for a Large tortoiseshell. It seems that under certain light conditions even dark legs of Large tortoiseshell can get a pale gloss. I noticed the same on the individual I saw last week, upperside of the butterfly is very typical for large tortoiseshell and in the field the legs looked dark but on some of my pictures the legs seem to have a golden gloss. A very big pitfall especially in the case of pictures from a certain distance where other features are not visible! Details on this observation can be found here:

Another picture of the Large tortoiseshell I saw on the 12th of March, the upper front leg seems rather pale, probably due to reflection to the small hairs on the leg. In the field the legs seemed all dark.

With these examples I hope you all keep on the lookout for Scarce tortoiseshells in the next few days and will have no doubt if you find one! Good luck!

Sunday, 8 March 2015

Spring for some... still winter for others...

As I made a call to look out for scarce tortoiseshell Nymphalis xanthomelas a few days ago, I couldn't stay inside today. So I decided to get on my bicycle and go to a forest some 20 km from home. Some butterflies were on the wing, comma Polygonia c-album and brimstone Gonepteryx rhamni. I also saw my first small tortoiseshells Aglais urticae.

No luck for the big shot for me, unlike in the Netherlands where already 4 scarce tortoiseshells were seen this weekend!
But I wasn't totally unlucky. After some searching I found 2 very small caterpillars of white admiral Limenitis camilla. Both were still in their hibernaculum, their winter stay made up of the remainings of the honeysuckle leave they fed on before winter and attached with some silk to secure during harsh winter.

Thursday, 5 March 2015

First spring butterflies in NW-Europe

In Belgium sun was shining today, wind was calm and temperatures rose to more than 10 degrees Celsius, for the weekend temperatures of even up to 14 degrees are predicted. Spring is clearly in the air and this means that butterflies wintering as adult will start to fly again. Today I was lucky to be on fieldwork and during work I already saw 3 butterflies; a red admiral Vanessa atalanta, a comma Polygonia c-album and a male brimstone Gonepteryx rhamni.

a spring 2012 picture of Gonepteryx rhamni

So for the weekend keep your eyes open; apart from the above mentioned species also peacock Aglais io and small tortoiseshell Aglais urticae will start to fly, some of you may even have the luck to see a large tortoiseshell Nymphalis polychloros. Also don't forget the influx of Nymphalis species last autumn in NW-Europe. Dozens of Scarce tortoiseshell Nymphalis xanthomelas were seen in the Netherlands and the UK, a few even reached Belgium. Undoubtedly some of them will have survived winter and will reappear in the next few weeks. Last autumn I gave a presentation for the Flemish butterfly studygroup on range shifts in NW-European butterflies that contained a slide on recognition of scarce tortoiseshell. Maybe not a bad idea to repeat it here to remind you all of the main features.
Scarce tortoiseshell on the left, large tortoiseshell on the right; all mentioned features are for scarce tortoiseshell and especially feature 4 and feature 6 are constant and the features to look at first.