On the day that the Natural History Museum in London has asked to keep my Berberis sawfly larva specimen (see 8 November post) for its collection, and The Sawfly Study Group Newsletter has asked to publish some of my Berberis sawfly larvae photos, I think it only right that I at last tell the tale, as promised in my first post on this blog, of how I came to find and, more importantly, to identify these history-making creatures. Let me tell you, dear reader, it was not easy …
Are you sitting comfortably? Then I’ll begin …
It was just after lunch on Sunday 15 October 2006. I was mooching round our small garden in Heslington, as is my wont, having a look at what was going on. When I got to the berberis bush in the corner I noticed that some of its leaves were rather well nibbled. I turned over a partly nibbled leaf to see if I could see what was doing the nibbling, and was surprised to see something I’d never seen before. It was (I thought) a caterpillar, with a black head, a white body with yellow and black spots, and six black legs. Very striking!
I looked more carefully at the bush as a whole (which is only about 4’ tall by 3’6 wide), and found 15 of these creatures – seven of them grouped together on one stem. None of them was moving.
Not only did I find a lot of caterpillars, I had the privilege of finding lots of poo too, both on the leaves of the berberis itself, and on the leaves of the geraniums growing underneath, which were carpeted with poos! To my untutored eye, these poos were disproportionately large in comparison with the creatures’ girth.
I took photos with a view to identifying the creatures later in the day.
Later in the day, I still hadn’t managed to identify them. I’d looked through all my butterfly books and my Field Studies Council Guide to the Caterpillars of the Butterflies of Britain and Ireland, and couldn’t find a caterpillar that looked like these ones.
So I decided they must be moth caterpillars. And who better to tell me which moth than moth expert Dr Dave Chesmore, who works just round the corner from me, at the University of York.
I sent Dave a photo of my caterpillars. The email bounced. Only it wasn’t until several days later that I realised that the email that had been returned to me was the one that I’d sent to him. So, on Friday 20 October I resent the email. Which was when the fun really began.
Dave Chesmore got straight back to me and said he thought it likely they weren’t moth caterpillars at all, but sawfly larvae. He said a good way of telling was to examine the number and distribution of their pseudopods (also called pseudolegs). Butterfly and moth caterpillars have a gap before the final pair of pseudopods; sawfly larvae don’t.
Sawflies? Pseudopods? My education was proceeding at a rapid pace. Having only seen three pairs of legs at the front of these creatures’ bodies, I had no idea they had any ‘pseudopods’. Off I went to have a closer look.
I found a berberis leaf with a ‘mystery creature’ on, and tore the leaf off the bush. I set the leaf against a contrastive a piece of white card, and set about trying to resolve The Pseudopod Question.
This turned out to be slightly more tricky than I had anticipated, as getting the creature to lie straight and upside down was, well, impossible. Its natural inclination, if disturbed, was to curl up. Hmm …
So, I got a twig, coaxed the creature onto it, and held both up against the white card background. Sure enough, on serious peeking, I managed to discern tiny pseudopods in line after the big black legs. Well I never! The key question was: was there a gap before the last pair of pseudopods or not?
Answer: I couldn’t tell. Try as I might to see what was going on at the rear end of the creature, I couldn’t, as it insisted on curling its ‘tail-end’ around the twig.
I took as many pseudo-pseudopod photos as I could, then admitted defeat and returned the creature to the berberis bush, whence it had come. I then went to have a look at the photos on my computer. Blown up on my monitor, the pseudopods were fascinating (they were really too small to see clearly with the naked eye). But as far as I could see, the photos I had managed to get still didn’t answer definitively the caterpillar/sawfly larva question. I sent the best photo I had to Dave.
He got straight back to me with an answer: sawfly larva. Apparently, all this tail curling was typical of sawfly larvae!
At last, five days after first spotting these creatures, five days during which I had visited them regularly and got to know them quite well (intimately, in fact, as on Tuesday I had had the dubious privilege of watching one of them do one of its majestic poos), I at last knew what they were. Sawfly larvae. Mystery solved.
Or was it? As it turned out, far from being the end of this story, this turned out to be just the beginning …
So, sawfly larvae they were. The next question of course was: what sort of sawfly? I opened my trusty Collins Complete British Insects and started looking. Aha – easy. There was a picture a gang of larvae identical to mine: Croesus septentrionalis. So, that was that.
Except of course that it wasn’t. When I went to bed that night thre was something niggling at the back of my mind. According to the Collins, Croesus septentrionalis, if disturbed, ‘raise their rear ends in unison’. Our larvae didn’t do this. Well, not that I had seen. In fact, they seemed to do precisely the opposite, as my vain attempt to view their rear pseudopods had demonstrated. Hey ho, there must be some explanation …
Next morning, Saturday 21 October, I got up and turned the computer on to type up the next two verses of the sawfly larvae poem I had come up with overnight. Whilst waiting for the computer to start up, I was leafing idly through my Collins when I stumbled on another, larger, photo of Croesus septentrionalis. And immediately something struck me: this photo showed larvae with three pairs of yellow legs. Our sawfly larvae very definitely had three pairs of black legs! Either our larvae were at a different, black-legged, stage of development. Or … ours were a completely different species altogether … How to find out?
I went online and, for want of anything better, typed ‘berberis’ and ‘sawfly larva’ into Google. From the results, I clicked on a link to the wildaboutbritain site. And there I discovered … that there was such a thing as the Berberis sawfly (Arge berberidis), that it was native to Central and Southern Europe, but that since 2002 a few sightings had been made in the south of England. Another Google search yielded an image of Berberis sawfly larvae. They had black legs, and looked remarkably similar to the ones in our garden.
At that point it dawned on me: maybe I had the world’s first ever sighting of Berberis sawfly larvae in Yorkshire! Maybe … or maybe not! How to find out?
The wildaboutbritain site mentioned experts at the Natural History Museum in London and the Royal Horticultural Society in Wisley who were tracking the spread of the Berberis sawfly larvae across the UK. So, I set about trying to contact these people. I needed to know firstly if the larvae in our garden were indeed Berberis sawfly larvae and if so, whether they’d ever been sighted in Yorkshire before.
Was entomological history being made in our garden? Or not?
I waited for a reply. I waited and waited and waited. And then, on 28 October, two whole weeks after I’d first spotted them, the answer came. As you can read, at the very first post to this website …