Summer solstice at Dundreggan

On Saturday 22nd June, the day after the summer solstice, I went out to Dundreggan, to celebrate the longest day of the year with a day’s photography in the forest there. At mid-summer we get about 20 hours of daylight in the north of Scotland, and it never gets fully dark. Even at midnight and 1 am, there’s always some light over the horizon in the north of the sky. I wasn’t planning to stay out that late though, but I was looking forward to enjoying the lush growth and abundant life of the season, as we officially moved from spring into summer.

Although the solstice is the longest day of the year, and is called mid-summer’s day, in biological terms it is more realistically the start of summer. In our part of the world, trees such as aspen (Populus tremula) and oak (Quercus petraea) only got their new leaves in early June this year, so the solstice is very near the beginning of their growing season. It’s also the start of the breeding season for many insects, and soon after I left my car and began walking in the forest this day, I came across a patch of nettles (Urtica dioica) which had caterpillars of the small tortoiseshell butterfly (Aglais urticae) feeding on them.

After hatching, these caterpillars spin a communal web, within which they feed initially, safe from predators. As they grow, they emerge from the web to feed more widely, and this was the stage they were at when I saw them.

 

 

 

 

 

 

 

This species utilises the ‘safety in numbers’ approach to ensuring that some young reach adulthood, as caterpillars in general, being relatively immobile, are very susceptible to predation by birds. To reduce the chance of predation, small tortoiseshell caterpillars, when they are disturbed, will flick their bodies from side to side in unison, doing a sort of lepidopteran impression of Medusa, with her hair full of twitching snakes.

While I was looking at the caterpillars on the nettles my eye was drawn to a larger shape on the leaf of a nearby nettle plant. It was a large beetle (Dascillus cervinus) – a species which is quite distinctive as it is covered in pale brown hair. Sometimes called the orchid beetle, it is about 1 cm in length and is distributed throughout the UK – I’ve seen it at Dundreggan before, in previous years.

On a another nettle plant a few feet away, I spotted a spider, and when I looked closer, I saw that there were actually two spiders – a  male and female appearing to be interested in courtship. The male was very cautious about approaching the female – an understandable action given the reputation that some female spiders have for eating suitors, often after mating. I didn’t wait around to see the outcome of this particular courtship, but enjoyed watching them for a few minutes nonetheless.

As with many spider species, the male was smaller than the female, and is also distinguished by the presence of his palps. These are appendages which are used for transferring sperm to the female, and which sometimes look like miniature boxing gloves – they can be seen clearly in the photograph here to the right. This species is quite common in our project area, and I’m grateful to Edward Milner for confirming the identification for me.

The more time I spent with this small patch of nettles, the more of interest that I saw. Returning to one of the plants with the small tortoiseshell butterfly caterpillars on it, I noticed a fly on one of the leaves. This was quite orange in colour and I subsequently had it identified as being a female of a species (Tetanocera elata) that is a parasitoid of slugs. (A parasitoid lays its egg in a host and the larva kills the host as it develops and grows, whereas a parasite will feed off its host without killing it).

Not far from the nettle patch are the only three mature ash trees that we have on Dundreggan, and I took some time to visit the largest of these.

 

 

 

 

 

 

 

 

 

 

 

 

 

The tree had only come into leaf about 3 weeks previously, and as it was a wind-still day, I was hoping to get some good images of it.

Ash trees have been in the news a lot in the past year, as a disease called Chalara is affecting them. It has devastated ash trees in parts of Europe, such as Denmark, where it has affected up to 90% of the trees, and has spread to the UK, on trees imported from the Continent.

The Chalara disease has been observed on some trees beside Loch Ness, but there’s no sign of it yet on our trees at Dundreggan. Because there’s only a handful of them on the estate, and they’re relatively distant from those at Loch Ness, I hope they won’t be affected by it.

Leaving the ash tree, I stopped to photograph a fly I saw on an unfurling frond of bracken (Pteridium aquilinum). This was later identified for me as being a female of a species (Thricops semicinereus) which is not associated with bracken – it was just using the bracken as a resting place.

Continuing along the outside of the enclosure we have the wild boar in at Dundreggan, I came to a patch of autumn hawkbit (Leontodon autumnalis), where there had been some aphids (Uroleucon leontodontis) feeding last year. There were aphids there again now, but when I sent the photos here to two different aphid experts, I got two different species names back from them! In late July there are a couple of aphid surveyors coming to Dundreggan for a week, so their visit may resolve the identity of them then.

There was some more bracken on the other side of the track from the autumn hawkbit plants, and when I had a close look at it, there were invertebrates utilising it as well. A bright green shape was the very distinctive cucumber spider (Araniella cucurbitina), sitting near the end of an unfurling frond of the bracken. It’s interesting to me that the two most readily-identifiable spiders in our area are both named after food – the other one is the strawberry spider (Araneus alsine)!

On another nearby bracken plant, there was a small fly which had captured, and was feeding on, an even smaller fly. I photographed this and collected the specimen so I could get it identified – it was a predatory fly (Bicellaria intermedia) – but unfortunately I didn’t manage to get the insect it was feeding on. There’s a whole world of predator-prey relationships in the world of these small insects such as Diptera, the two-winged flies, that I’ve barely begun to find out about …

While I was looking at the bracken, I saw a different insect on another frond, and recognised it immediately as a stonefly. Stoneflies form the insect order Plecoptera, and their larval stage is spent in freshwater, with the adults often being seen in spring or early summer near water, where they will just have emerged from their pupae. My colleague Colin Hall, who has a keen interest in stoneflies, identified this one for me as being a common species, Nemoura cinerea.

I walked on for a while, heading for a stand of aspen trees a little to the west in the woodland. During the aphid survey at Dundreggan last year, we’d found three different species of aphids on the trees in the stand, and I wanted to see if they were present again this year. On a visit a couple of weeks previously I hadn’t seen any aphids on the aspens there, and in general there seems to be far less aphids on all the trees than in 2012.

I searched for a while, but didn’t see any sign of aphids at all. However, there were a lot of small shiny metallic-looking beetles on the leaves of the aspens. These are a species of leaf beetle (Phratora vitellinae) that are quite common on aspens in our area, and I came across a pair that were mating, so I stopped to take a few photographs of them. There seemed to be more of these beetles than in other years, and I wondered if there was a connection between there being fewer aphids but more beetles? Could it be that the same combination of weather and other conditions that has caused a significant drop off in aphid numbers from 2012 had somehow favoured these beetles instead?

My final destination for the day, as it turned out, was a juniper bush (Juniperus communis) about 400 metres west of the lodge at Dundreggan. This particular bush was one of two where Ed Baker, who did the aphid survey of the estate in 2012, found an aphid species (Cinara smolandiae) never recorded in the UK before. He’d asked me to keep an eye out for more aphids there this year, so this was one of the days I’d planned to have a look at it.

Ed had originally thought the aphids in question were a species called Cinara mordvilkoi, but subsequent correspondence with other aphid specialists led to the conclusion it was Cinara smolandiae. The bush itself had featured in a short STV news clip about biodiversity at Dundreggan that was broadcast earlier this year. This day, however, there was no sign of that species on the bush – it was only the common juniper aphid (Cinara juniperi) that I saw, being tended by wood ants (Formica lugubris).

I headed back to the car park, so that I could drive back home, but before I left, I checked the interpretation boards there, as I’d seen some small insects on them when I’d arrived in the morning. These had quite distinctive markings on their wings, and as they were still there at the end of the day, I collected one for identification and for photographing under controlled conditions at home. It turned out to be another predatory fly (Tachydromia umbrarum). My solstice trip had turned into a veritable insect lover’s day therefore, and I’m very grateful to Peter Chandler for his help in identifying this species here, and the other Diptera featured in this blog.