Leafmines: Stigmella viscerella

18 Monday Aug 2025

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British leafmines, leaf-mining moth larvae, leaf-mining moths, leafmines on Wych elm, Stigmella viscerella, Wych elm

I’m often surprised when I find a new leafmine: how is it that I’ve not noticed this one before, and how many different leafmines can there be? The answer to the first question has to be that I haven’t been paying enough attention, and to the second that there are probably hundreds that I haven’t yet found.

Today’s new leafmines were made by larvae of the moth Stigmella viscerella, and the mines can be found on the leaves of Elm trees, in this case Wych elm (Ulmus glabra), during August and September. Now that I’m aware of them, I’ve managed to find the mines in two different locations on two separate days, which is why the elm leaves in the two sets of images look different in colour (one day was brighter than the other).

The epithet viscerella may seem odd – it comes from the Latin viscera, plural of viscus, and refers to the human body’s internal organs – but when I look at these mines, the twisting shapes of the frass-filled galleries do, indeed, remind me of human intestines. I presume that the adult moth is not often seen as the UK Moths website doesn’t have its photo but, if you’re curious to see what emerged from these ‘intestines’, I managed to find an image on the German Lepiforum website.

Elm bark beetle

19 Wednesday Feb 2025

Posted by sconzani in insects, trees

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dead Wych elm, Dutch Elm disease, elm bark beetle, elm bark beetle tunnels, Large elm bark beetle, Scolytus scolytus, Wych elm

After last Friday’s post about the Velvet shanks I’d found on a dead Wych elm, it occurred to me that I couldn’t recall seeing any traces of the elm bark beetles (likely the Large elm bark beetle Scolytus scolytus, according to an article on the Forest Research website) that carry the fungus that killed the tree. So, I went back for another look, and it turns out I hadn’t looked closely enough: there were signs of beetle activity all over the exposed areas of trunk where bark had fallen away and this showed up much more clearly on the darker underside of the bark itself.

During the summer, the female elm bark beetle drills a hole through the tree’s bark, then creates a long straight burrow (called the mother tunnel) under the bark. As she excavates, she lays eggs and, when the larvae hatch they create their own tunnels outwards from the mother tunnel. If the effects of their presence weren’t so deadly, the tunnels could almost be viewed as tiny works of art.

A Cladius on Wych elm

05 Thursday Oct 2023

Posted by sconzani in insects, trees

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British sawflies, Cladius sawflies, Cladius ulmi, Cladius ulmi larva, sawfly larva, sawfly on Wych elm, Wych elm

There are just seven species of Cladius sawfly found in Britain, which, you might think, would make them relatively easy to identify. Sadly, this isn’t the case, especially in their larval forms, as all their caterpillars look very similar, and even the expert I consulted said he was unsure about the larval differences.

231005 Cladius ulmi (1)

However, I seem to have struck it lucky with this particular species as The Sawflies (Symphyta) of Britain and Ireland website says: ‘They can be distinguished from the other elm feeding species, Cladius rufipes, by the presence of a black spot on the front of the face which is absent in rufipes.’ As you can clearly see in the photo above, this larva has that black spot, so meet Cladius ulmi, a sawfly species that feeds on elm, in this case Wych elm (Ulmus glabra).

231005 Cladius ulmi (2)

A White-letter hairstreak

22 Saturday Jul 2023

Posted by sconzani in insects, trees

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British butterflies, butterfly, butterfly in Wych elm, White-letter hairstreak, Wych elm

Last Saturday’s weather was rather different to today’s constant rain – there was rain, but interspersed with warmer, sunny spells, and I managed to coincide my visit to local Dingle Park with one of those. This was my third time standing staring at the park’s Wych elms, and it was definitely a case of third time lucky.

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Previously, the White-letter hairstreaks had stayed high in the tree but, this time, one little beauty came down lower, wandering slowly across the leaves, all the while with its tongue out, licking up the tasty honey dew.

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Initially, it was quite distant but my patience paid off as it flitted from one cluster of leaves to another until it was really quite close. White-letter magic!

230721 white-letter hairstreak (3)

Cocoon

08 Saturday Jul 2023

Posted by sconzani in insects, trees

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Aproceros leucopoda, Elm zigzag sawfly, Elm zigzag sawfly cocoon, insect cocoon, leaf damage by Elm zigzag sawfly larvae, Wych elm, Wych elm leaves

At this time of year, whenever I spot a Wych elm tree, I spend a bit of time staring at the leaves. I look for two things in particular: the first is to see if I can spot any White-letter hairstreak butterflies flitting around, usually at the top of the tree but also lower down; and the second is to see if anything has been nibbling at the leaves. My searching paid off last week when I spotted the distinctive signs of leaf damage caused by the larvae of the Elm zigzag sawfly (Aproceros leucopoda), not necessarily a good thing as this is an invasive species, which I found new to Wales in October 2021 (Zorro comes to Wales) and which is now slowly spreading westwards. But, more interestingly in this particular case, I found one of the cocoons the larvae pupate in, a very delicate, woven-silk structure (you can see an occupied cocoon on the Forest Research website). This one was empty so I guess that’s one more adult sawfly helping to spread the species further.

230708 elm zigzag sawfly cocoon

The return of Zorro

14 Saturday May 2022

Posted by sconzani in insects, leaves, trees

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Aproceros leucopoda, Elm zigzag sawfly, sawfly larvae, sawfly on Wych elm, Wych elm

If you’ve been following along here for a while, you might remember last year’s ‘first for Wales’ find, the distinctive marks on leaves of Wych elm trees of the Elm zigzag sawfly (Aproceros leucopoda) (Zorro comes to Wales, October 2021). For the past couple of weeks I’ve been monitoring the trees where I first saw those marks and, yesterday, found them again, with the larvae that create them in situ, happily munching away on the elm leaves. In fact, following a good look around the area, I found larvae on six Wych elm trees (and there were other trees I couldn’t access), and then found a single larva on a Wych elm at Cosmeston, perhaps half a mile away. It will be interesting to see how quickly these creatures spread through the local landscape.

220514 elm zigzag sawfly larvae

White-letter hairstreak larva

26 Tuesday Apr 2022

Posted by sconzani in insects, trees

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British butterflies, butterfly larva, larva on Wych elm, White-letter hairstreak, White-letter hairstreak larva, Wych elm

In recent weeks I’ve been searching, unsuccessfully, for the eggs of Purple and White-letter hairstreak butterflies but … during Sunday’s woodland walk I did find this little beauty, my very first White-letter hairstreak larva. I was over the moon!

220426 white-letter hairstreak larva (1)

As you can see, its camouflage is excellent and I know I wouldn’t have spotted it if I hadn’t been looking so closely at the flower and leaf buds of this Wych elm. I couldn’t find any more larvae but I’ll return soon to this site for another look and, hopefully, will be able to re-find and observe this tiny creature as it grows.

220426 white-letter hairstreak larva (2)

Dothidella ulmi

29 Friday Oct 2021

Posted by sconzani in fungi, leaves, nature, trees

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British fungi, Dothidella ulmi, fungi on Wych elm, spots on Wych elm leaves, Wych elm

Fungi come in an amazing variety of forms and colours. Here’s one I found for the first time a week or so ago.

211029 Dothidella ulmi (1)

You’re probably familiar with Sycamore tarspot (Rhytisma acerinum), which makes black spots on the leaves of Sycamore trees. Well, this is superficially similar, though not as widely recorded in Britain: it’s Dothidella ulmi, a fungus that develops under the epidermis of leaves on Elm trees, in this case Wych elm, then erupts in a mass of grey blisters.

211029 Dothidella ulmi (2)

A white-letter day

09 Friday Jul 2021

Posted by sconzani in trees

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British butterflies, butterfly on Wych elm, hairstreaks, Satyrium w-album, White-letter hairstreak, Wych elm

I’m sure you’ve all heard of red-letter days, those days that are of special significance or particularly memorable. Well, for me, yesterday was a red-letter white-letter day – the day when I had my best ever views of the elusive White-letter hairstreak butterfly (Satyrium w-album).

210709 white-letter hairstreak (1)

These beautiful creatures spend most of their time in the tops of Wych elm trees (now that most English elms have died from Dutch elm disease) so my first sighting of them this year was typical – they were flitting around the top of a tree in a local park, far too distant for good views, let alone photos (see above).

210709 white-letter hairstreak (2)

Then, yesterday, I was walking in meadows adjacent to a local woodland, when I spotted this gorgeous White-letter hairstreak nectaring on a thistle right next to the path in front of me. I was able to photograph and watch it for at least 15 minutes before it flew back towards the nearby Wych elm. A white-letter day to treasure!

210709 white-letter hairstreak (3)