(Blog updated on 17th April 2012 to include details of the slime mould)
It had been two weeks since my last trip out to the Caledonian Forest, as I was busy last week-end, in between public talks on the Millionth Tree lecture tour that I’m doing throughout the UK in the second half of March and April. The weather had continued to be very mild and warm for the season, so a few days after the equinox I set out for Dundreggan, keen to see how spring was unfolding.
It was a wind-still day, with some haze in the sky as I travelled, and it was also very dry – it had been quite a few days since the last rain had fallen. Upon reaching Dundreggan, it looked like the sun would come out, and it felt very much like the quickening of spring was well under way. As I stepped out of my car in the car park, I was greeted by the distinctive song of chaffinches (Fringilla coelebs), who seemed to be celebrating the mild weather and relatively early sings of spring with their musical trilling.
Walking up into the woodland, I hadn’t gone very far at all when I came across the very fresh scat of a pine marten (Martes martes) in the middle of the track. It was still glistening wet, and must have been deposited there just a few minutes before I saw it – in these warm conditions it would dry up very quickly. As I looked at it, I wondered if the pine marten was still nearby, perhaps watching me from some hidden spot?
I’ve never seen a pine marten in the wild in Scotland – although many of my colleagues at Trees for Life have, I’ve never been in the right place at the right time somehow. The only time I’ve seen one was in British Columbia, Canada, many years ago. While many people might be put off by scat, I’ve learned that it can be interesting because of the life that is attracted to it.
In fact, as I looked at it, I noticed that a slug was exploring the scat, but, perhaps disturbed by my presence, it soon moved away. A fly that landed on the pine marten poo stayed for longer, moving over much of the surface while it was there. I couldn’t see whether it was feeding and/or laying eggs, but I sent the photo to a fly specialist, who has advised me that it is a female, and almost certainly a species called Lasiomma seminitidum.
Moving on, I had only gone about 20 metres further when I spotted some more pine marten scat, this time on a large rock. This one was obviously older, as it was much drier. I couldn’t help but think it must have been left by the same animal, who perhaps had its territory here. This drier one was just outside our wild boar enclosure, and that led me to think that maybe the pine marten was benefitting from the boars’ presence. Some research that we had done there last year indicated that there were higher numbers of small mammals such as mice and voles in the boar enclosure, so perhaps the pine marten was taking advantage of the increased availability of prey?
Nearby the rock there was an old fallen, partially rotten birch log, and when I peeled back a section of the loose bark on it, I found a very interesting sight. It looked like a cluster of sporocarps of an old slime mould, which had new white radial shoots growing out of them. I’d never seen anything quite like it before, and it was quite beautiful in appearance. The whole cluster was about two centimetres in length and it looked almost like something out of an alien landscape in a science fiction film.
I sent the photos off to Bruce Ing, the country’s leading expert on slime moulds, who I’ve been corresponding with for the past few years. I had only met Bruce for the first time just over a week previously, when I gave the first talk on the Millionth Tree Lecture Tour to the Lochbroom Field Club in Ullapool, which he’s the coordinator of. He replied that the photo shows the sporocarps of a slime mould (Trichia varia) that are parasitised by a fungus (Polycephalomyces tomentosus) that only occurs on myxomycetes (as slime moulds are called in scientific parlance).
At the same spot, my attention was drawn to a flash of something very small and bright red on the ground. Looking closely I saw it was a red velvet mite, a tiny invertebrate in the class of organisms known as arachnids, which also includes spiders, scorpions and ticks. As larvae, these mites often attach themselves as parasites to the legs of harvestmen, but this looked like an adult, and was possibly of the species Trombidium holosericeum, which is one the largest in the northern temperate region.
Moving on again, I came to some more fallen birch trunks, and when I turned over another piece of bark on one of those, I found a good example of fungal hyphae, the white thread-like filaments that make up the main body of a fungus, growing on the underside. The mushrooms that we see in a woodland, most typically in the autumn, are just the fruiting bodies of fungi. The main part of their structure is the network of hyphae which persist year-round underground – it’s only occasionally like this that they are seen.
Another piece of bark from the same fallen birch trunk had a different item of interest on its underside. A slightly conical shape rising up out of the bark had a narrow thread on top of it which led to a tiny orange balloon-shaped object that had a net-like growth over it. I don’t know what is exactly, but one suggestion that’s been made is that it’s the egg sac of an insect. In any event, this, and the fungal hyphae, illustrate the interesting but invisible world of Nature that exists inside something which most people will never give any serious attention to – dead wood on the forest floor.
I decided to have my lunch there, and as I ate I wandered around a little more, to see if there was anything else of interest in the vicinity. In fact, elsewhere on the same fallen birch log I found some cudbear lichen (Ochrolechia tartarea), growing on the external surface of the bark. This is one of the most easily-identifiable lichens, as it produces a large mass of brown discs on its surface. These are the apothecia, the structures that release the spores of the fungal partner in the symbiosis between fungus and alga that makes up the lichen.
One of the birch trees there had a large burl or burr growing on its trunk. These are caused when the tree experiences stress such as drought or fungal attack, and the unusual growth is filled with dormant buds.
There were a few old Scots pines (Pinus sylvestris) nearby, and I was drawn by one large tree in particular. As I looked closely at its trunk, I saw a small spider sitting on the bark. I was immediately interested by this, as when we had a spider survey done at Dundreggan in 2009, the arachnologist found a rare species (Dipoena torva) on the trunk of a pine like this in the same area. That species hunts wood ants on pine trunks, and I haven’t seen it myself, so I was wondering if this was it on this tree? I’ll have to send the specimen off to the specialist to get it identified, but whatever species it is, this individual is a male – the large palps (which look a bit like boxing gloves on this one!) are only found on male spiders.
While I’d been walking through the woodland I’d been aiming for a large wood ant nest, near some aspen suckers that we’ve protected with Netlon tree guards. The suckers are growing off the roots of some mature aspens, along the lower reaches of what we call the Aspen Burn – one of the smaller watercourses on the estate. In the summer, the wood ants tend aphids that suck the sap of the aspens, and although there wouldn’t be any aphids present at this time of year, I did expect the wood ants (Formica lugubris) to be active, given the sunshine and warmth of the day. Reaching the nest, I saw that it was indeed full of activity, with thousands of ants busy on the nest itself, moving small bits of forest debris around, and heading off on missions to look for food. I decided to settle down for a while and just watch the ants, as I sometimes do, because it’s often possible to see interesting behaviour at their nests.
In fact, I’d only been there for a few minutes when I spotted a group of ants dragging a caterpillar across the surface of their nest. The ants regularly hunt for caterpillars, which they provide to their larvae as a source of food. This was a caterpillar species I recognised, having seen ants at the same nest at this time last year with one they had captured. Checking with a moth expert later, he confirmed it as being of the square-spot rustic moth (Xestia xanthographa), and I watched for a few minutes as the ants hauled it over the nest and down one of their entrance holes into the interior.
Soon afterwards, I spotted another ant carrying something across the nest. As I looked closer I saw that it was possibly a small earthworm. In this case, a single ant was able to carry the prey item, whereas with the caterpillar it took quite a number of ants to move it, as it was so much larger than each individual ant. In areas like this, where they are abundant, wood ants can have a significant effect on the populations of insects and other invertebrates.
A little while later, something larger moving on the nest caught my eye, and I saw a group of ants struggling to haul a large beetle across the surface of the nest. This was a flightless ground beetle (Abax parallelepipedus) that is quite easy to identify, although I had to get a specialist to confirm the ID for me. Growing up to 22 mm long, it was a real challenge for the ants to move, and it took quite a number of them to do so.
It was very slow going for the ants, and sometimes they tried turning the beetle over, either on its side, or completely upside down, in order to transport it over or around the obstacles, such as twigs, on their nest. I watched their efforts for over an hour, and they barely moved it more than about 20 centimetres in that time. After walking around for a while, and meeting the volunteer group based at Dundreggan for the week, I spent another hour or so watching the action.
Eventually, after almost 3 hours of struggle, the ants managed to manoeuvre the beetle to one of their nest entrances, and they slowly dragged it down into the interior, where its fate was sealed. It was a marathon effort on their part, and a testament to their effectiveness as small predators, that they’re able to capture and transport insects like this that are so much larger than each individual ant.
I was also shooting some video of the ants, so here’s a compilation of some of the best footage:
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Just when I thought I’d seen all the action at this ant’s nest for the day, because the sky had clouded over and in the cooler temperatures there were fewer ants active, an ant arrived at the nest with another item of prey – a spider in this case. One or two other ants came along to help, but it was much easier to manipulate and move across the nest than the large beetle had been, and it was rapidly taken down into the interior.
I decided to move on too, and headed back towards my car, via the small slope where I’d seen the first primrose (Primula vulgaris) of the year in flower on the 25th of February. There were a lot more plants in flower by this time, four weeks later, and many of them were just in their prime, with the individual blossoms looking very fresh and still perfect in their form.
They hadn’t reached their peak of flowering yet though, as I could see a lot of other plants where the buds hadn’t opened yet. In previous years, at the height of flowering on this slope (which is usually in late April, but it’s certain to be earlier this year, because of all the warm weather we’ve had in March), it can be hard to walk there, because the primroses are so abundant and growing closely together. That’s a delight to look forward to in another 2 or 3 weeks time!