Wych Elm Galls

June 8th was a beautifully warm, sunny day; one which simply demanded my attention. I took myself up the hill and approached Uig Wood from its uppermost slopes, I had flies in mind! The image below shows the area where I spent a happy hour or so, swiping at sunbathing sarcophagids amongst a multitude of smaller dipterans. 

Sunlit, out of the wind, decidedly warm and without midges - a rare combination up here! 

Hidden beneath the sweeping boughs of these trees lies a sheep fence, topped with barbed wire. Thankfully, it does a grand job of keeping them out of the woods (as you can see, everything to the left in this image has been grazed to within an inch of its life). Don't get me started on the sheer mindlessness of rearing these awful woolly maggots, though the lost lamb pathetically bleating for it's mother was kind of cute as it spied me and slowly approached from a few hundred feet away to within about fifteen feet distance. Sorry buddy, I can offer you a can of Relentless or a swift kick up the backside, but nothing in the way of milk or motherly affection. I did briefly contemplate wrestling it into a headlock and checking the fleece for interesting critters, but it BAAAAAA'ed its way back over the crest of a hill and left me alone. Must get myself a haircut sometime soon. 

Anyway...

So I potted a handful of sarcophagids (I'd ordered the book on 23rd April. It arrived three days ago) and various other bits n bobs, and then suddenly noticed this weird-looking thing on a Wych Elm leaf

As galls go, that's actually pretty damned impressive!

I have a terrible memory when it comes to recollecting the name of something I've seen before. It doesn't matter if it was five years or five hours ago, I'm just truly abysmal at remembering scientific names. However, I am pretty good at knowing whether or not it's something I've seen before. And so, as I found myself staring at this monstrous leafy protuberance, I knew without a doubt that I'd never seen anything like it before. And then I spied more of them 

This latter image shows an earlier stage of gall development

There are lots of organisms that cause galls to develop in leaf blades, ranging from fungal attack to mite infestation, from bacterial infection to nematodes, from aphid colonies to insect larvae. I suspected aphids or flies in this instance, mostly due to the size of the thing. 

I collected one large specimen and, after I'd finally done swiping my net at flies, headed indoors to examine my find. Before that though, I jumped on the Book of Faces and promptly discovered that Stephen Bungard, professional botanist, BSBI county recorder and amateur all-round (and rapidly diversifying) naturalist had posted up pics of the exact same gall which he'd just found, and later blogged about, from neighbouring Raasay. Beaten to it by a couple of hours! Anyway, he'd already sussed the culprit and saved me the bother, though I still sliced it open and checked the contents for myself

This big old lonesome aphid, which went so far as to slowly rock back and forth (shuffle would be going too far, I feel) was the only thing I found inside the gall. Looking at the size of it, I did wonder if it hadn't already eaten the rest of the colony! Following up Stephen's identification, I concluded that he was bang on with Tetraneura ulmi, an aphid that causes spectacular galls on Ulmus leaves. And when I say spectacular....

 https://bladmineerders.nl/parasites/animalia/arthropoda/insecta/hemiptera/sternorrhyncha/aphidoidea/aphididae/eriosomatinae/eriosomatini/tetraneura/tetraneura-ulmi/

I'm hoping that by providing Bladmineerders' link to the species as a caption I can somehow bypass any untoward copyright infringement. Probably not, but the Dutch are generally quite a lenient bunch. Usually. 

Stephen mentioned that there were only four post-1998 records for the Highland Region, all of which were submitted via the HBRG. In the space of a few hours we'd unwittingly upped that by 50%, and then Neil took himself down to Tora and found it there as well, so from four to seven records and the first for some years! HBRG now have a Forum, still very much in it's infancy, but it looks useful (if ever I can log into it...) and the matter of this gall's sudden appearance now has it's own page here.

But we shouldn't get too far ahead of ourselves; it turns out that there are a whole host of aphid-induced galls on Ulmus. Thankfully ours seem to be pretty clear-cut Tetraneura ulmi, but others include Kaltenbachiella pallida, Colopha impressa and Eriosoma lanuginosum. There are also several further aphid species found on Ulmus which cause leaf puckers, bulges, curls and rolled rims, namely Eriosoma ulmi (which I've recorded here before), Eriosoma anncharlotteae, Eriosoma flavum, Eriosoma patchiae and Eriosoma grossulariae. Luckily they all have slightly differently formed galls and the aphids themselves are diagnostic in colour and morphology, so they ought to be identifiable should I happen to find any of them. Still, it's something to be aware of and to look out for. Some of these species switch to a secondary host midway through the year, which could be in the roots of various grasses. So I need to get a handle on them now, before they effectively 'disappear'. 

Talking of roots...