September is a month of transition in the Caledonian Forest, with summer coming towards an end, and the first signs of autumn appearing as the bracken (Pteridium aquilinum) begins to change colour. However, there’s still a lot of life visible at this time of year, and so I was glad to have the opportunity of spending a Saturday at Dundreggan in the middle of the month purely for photography. I had some thoughts about going to one of the more distant parts of the estate, but as it transpired, I didn’t get further than about a 10 minute walk from the lodge, because there was so much of interest nearby!
Yellow is one of the prominent colours in the forest in September, with the fronds of bracken turning bright yellow before they die back for the winter, and the first of the birch leaves also showing some golden hues. At the edge of the woodland, ragwort is a brilliant yellow colour when it is in full bloom, and is possibly the most important food source for a wide variety of insects at this time of year. Just outside the field where our tree nursery is located at Dundreggan, there are quite a few patches of ragwort, and when I reached them I saw they were teeming with life.
It was a sunny day, and the warmth and brightness meant that there were a lot of insects on the wing, many of them utilising the ragwort. First to catch my eye were the small delta wing-shaped moths called nettle-tap (Anthophila fabriciana). This species derives its common English name from its larval food plant, the common stinging nettle (Urtica dioica), and indeed nettles grow very near this patch of ragwort. The moth is on the wing from May onwards, but I most commonly see them in September, feeding on ragwort like this.
There were quite a lot of them on the ragwort plants, and as I looked at some of them I noticed a caterpillar on one of the flowers.
I suspected that this was a caterpillar from one of the pug moths, and this was subsequently confirmed by Roy Leverton, a specialist in caterpillars who helped me with identifications, when he told me it was the wormwood pug (Eupithecia absinthiata). While I watched, the nettle-tap moth moved around on the ragwort flower, approaching the caterpillar, and then climbed over it, like it was just another part of the flower itself, to reach the next blossom.
There were a number of caterpillars on several of the ragwort plants, and some of those at least looked like the same species. This one in the photograph here was one that Roy thought was probably an early instar of the wormwood pug. Instars are the different stages of growth of caterpillars, with a moult in between each of them, when they outgrow the previous ‘skin’. They seemed quite at home on the ragwort flowers, and their colour was similar to that of the blossoms, in an example of the phenomenon of camouflage in nature, which is utilised by a lot of moth and butterfly caterpillars.
On another nearby ragwort plant I spotted a different caterpillar. This was one I’d seen before, but I couldn’t remember what species it was. Roy later identified it as the golden-rod pug moth (Eupithecia virgaureata).
With so many insects attracted to the ragwort, there were inevitably predators waiting to catch them. Straddling a couple of the flowers, waiting motionless for an unwitting invertebrate to come close enough, was a harvestman (Mitopus morio). This is a common species, in the same Class in the scientific system of biological classification as spiders – the Arachnida. Like spiders, harvestmen have eight legs, but they only have two eyes, whereas spiders have eight.
On another ragwort plant I saw a spider hanging on its web between some of the flowers, and my friend Edward Milner identified it as a female of a common species (Metellina segmentata).
By this time I had really had my eye in for spotting different insects on the ragwort plants, and because the sun was out, there were plenty of hoverflies feeding on the flowers. There are many species of hoverflies and quite a number of them sport black and yellow markings, making them similar in appearance to bees and wasps. This is known as mimicry, and in particular this is an instance of Batesian mimicry.
Taking its name from Henry Walter Bates, an English naturalist in the 19th century, Batesian mimicry describes the phenomenon whereby harmless species (in this case hoverflies, none of which sting or bite) closely resemble much more dangerous insects – bees and wasps. This provides protection from predators such as birds, because any bird which attempted to catch a wasp or bee and has been stung will avoid similar looking insects in future. There’s considerable variation in the colouration of black and yellow hoverflies, which is how to tell the species apart, but they all exhibit the same message – ‘stay away from me, because I look like I’m dangerous’. This is of course a bluff on the part of the hoverflies, but it’s a superb evolutionary adaptation that is obviously beneficial to them.
In the space of just a few minutes I photographed four different species of hoverflies on several of the ragwort plants.
Near the ragwort there was some bracken and a slight movement on one of the fronds caught my eye. Turning to have a closer look, I saw that it was a froghopper, and I thought that it was the species I most often see – the common froghopper, or spittlebug (Philaenus spumarius) – whose larvae produce the distinctive patches of ‘cuckoo spit’ on vegetation in early summer. However, when I sent the photo to Joe Botting, an expert on bugs who’s done several surveys for us at Dundreggan, he replied that it was a different species – the alder spittlebug or froghopper (Aphrophora alni). The common froghopper is quite a variable species and some of its colour forms resemble the alder spittlebug, so I’m not the first person to have got the two species confused.
Returning my attention to the ragwort plants, I noticed another insect that I often see on ragwort at this time of year. It was a plant bug – like the alder spittlebug, it is a member of the order of insects known as Hemiptera.
As he’s done in previous years when I’ve asked him about this bug, Joe stated that this is a member of a genus (i.e. Lygus) that is very hard to separate into species, but he’s reasonably confident that it’s one called Lygus wagneri. There were quite a few of these plant bugs on the ragwort flowers, and one of them was right next to a much larger insect – the ear moth (Amphipoea oculea).
The adults of this species are reportedly attracted to ragwort flowers, and indeed I see them on some of those plants at this time every year at Dundreggan.
Ragwort has a bad reputation as a plant, and is systematically weeded out of many meadows and fields, because it is poisonous to mammals, particularly horses. However, horses generally don’t eat the living plants, but are unable to distinguish dried ragwort in a bale of hay, so they unwittingly consume it there, and then suffer liver damage. This is apparently how the majority of poisoning incidents occur. Ragwort provides a crucial source of nectar and pollen for many insects at the end of summer, when there is a limited range of food available for them. Its removal from many places must undoubtedly be having an impact on insect populations and the species that feed on them, such as many birds. I hope that in future humans can develop more wildlife-friendly systems of animal husbandry, that enable us to share more of the Earth with the wonderful diversity of species that live on the planet with us.
I began this blog by writing about the changing colour of bracken in September. However, by the time I was ready for a break for lunch, I hadn’t made it past the ragwort patch, not far outside our tree nursery field, and hadn’t reached any significant areas of bracken yet. Because of the length of this blog, it’s another one I’ve decided to split into two separate parts, so this is a good point to take a break. I did, of course, find lots of other subjects of interest to photograph, as well as the bracken, and coming up in part 2 are wax cap fungi, caterpillars and galls on aspen trees (Populus tremula), a slime mould, and video footage of wood ants (Formica lugubris) tending aphids on aspen and juniper (Juniperus communis). It was indeed a day of wonders in the forest …