Unseen biodiversity of Glen Affric, part 3

This blog follows on from Part 1 and Part 2 in this series with the same name, covering some of the species and ecological relationships I observed in Glen Affric during my visits there in 2018. It picks up the story in the middle of August, when the forest was full of a wide diversity of insects, many of them feeding on the flowering plants that flourish in the later stages of summer.

Some of these were common species, and angelica (Angelica sylvestris) is a good host for a wide variety of flies, beetles, hoverflies and bees, that are all attracted by its umbels of creamy-white flowers. The bee beetle (Trichius fasciatus) is one of the more spectacular and easily-identified visitors, with the black and yellow markings on its elytra fringed by a mass of white hairs creating a remarkably good mimicry of various bumblebees. This phenomenon in nature, whereby a harmless species takes on the colour and form of one with more aggressive behaviour, such as powerful stings, is known as Batesian mimicry.

In addition to being very distinctive, the bee beetle is quite large, at about 1 cm. in length. Also feeding on the angelica plants were some much smaller reddish brown beetles that turned out to be three species in the same genus, Epuraea.

I was able to get these identified thanks to the expertise of Sholto Holdsworth at the Natural History Museum in London, who provides invaluable assistance to me with beetle ID queries.

By this time of year devil’s-bit scabious (Succisa pratensis) is just coming in to flower, and it also attracts a lot of insect visitors. Its distinctive bluish-purple blossoms are unmistakable, and even before they are fully open flies and hoverflies will land on them to feed. In some areas of the forest, this is one of the most important nectar sources in late summer, as devil’s-bit scabious will continue flowering after most other plants have finished.

Its common name is rather unfortunate for such an attractive flowering plant, with ‘scabious’ being derived from the fact it was used to treat scabies caused by the plague and other diseases in medieval times. The other part of its English name comes from the belief that its short black root, which ends abruptly, had been bitten off by the devil, apparently in anger at the plant’s ability to treat and heal people from these illnesses.

By the middle of August fungi are beginning to appear in good numbers on the forest floor, and it’s a time when I collect chanterelles (Cantharellus cibarius) for cooking and eating at home. When I was picking some I noticed an invertebrate on the gills on the underside of the cap of one of them. It was a harvestman, which is an Order of arachnids in the same Class as spiders in the scientific system of classification of organisms. This one was a small, readily-distinguished species (Nemastoma bimaculatum) that preys on small invertebrates.

On my next visit to the glen, about 10 days later, I came across another fungus, which although it is fairly common, is probably overlooked by many people. This was the ergot fungus, which affects grasses and some cultivated cereals such as rye. It manifests as a purplish-coloured curved cylinder, known as a sclerotium, protruding from the seed head of the grass. This consists of a hardened mass of fungal hyphae that can remain dormant until the sclerotium falls to the ground, where they begin to grow as a new fungal mycelium.

One of the places I visited on that day was the picnic area for visitors on the north shore of Loch Beinn a’ Mheadhoin. While I was walking around I noticed some yellow rattle plants (Rhinanthus minor) in a grassy section of the forest floor. This is an interesting plant, as it is hemi-parasitic, taking some of its nutrients from the roots of other plants. It also photosynthesises its own food and has distinctive yellow flowers clustered together on the end of stalks.

I knew from the aphid survey I commissioned for Trees for Life’s Dundreggan Conservation Estate in 2015 that there is a species of aphid that feeds inside the flowers of yellow rattle. Although these plants here in Glen Affric had finished flowering, I decided to check them to see if there were any aphids inside the ripening seed cases or capsules that were visible on the plants. Imagine my delight then when the very first yellow rattle seed case that I opened turned out to have aphids (Hyperomyzus rhinanthi) feeding inside it!

This was the first time I had found these aphids myself, as at Dundreggan they had been found by the aphid surveyors, Bob Dransfield and Bob Brightwell, who showed them to me. I suspect this is also the first time these aphids have been observed in Glen Affric, as I’m not aware of any previous records for them there. In fact, there aren’t any records at all for this species on the NBN Atlas, which is the central information resource for biological diversity in the UK, but it has certainly been found in the country before and it appears that very few aphid records get uploaded on to that database.

I spent quite a while looking at these aphids, as I found them on a number of yellow rattle plants in the vicinity. One in particular caught my eye, as it had a red shape attached to it. This was a parasite – the larva of a red mite, similar to ones I’ve previously seen on other species of aphids. These larvae feed on the haemolymph of the aphids and drop off to pupate into adult mites, with the aphids surviving their attentions. Thanks to the help of Joanna Makol, a mite expert in Poland, I was able to get this larva identified as being a species of Allothrombium.

While I was looking at the yellow rattle plants for aphids I noticed an area of bright red-orange colour on a leaf of one. I recognised this as being a rust fungus – a group of many species that produce brightly-coloured fruiting bodies like this on the leaves of various different plants. When I sent the photograph off to Liz Holden, a mycologist who helps me with fungal identifications, she confirmed that it was most likely Coleosporium tussilaginis, a species that I had provisionally identified it as, from searching the Internet.

By early September more fungi were visible in the forest, and this year in particular there seemed to be a lot of honey fungi fruiting on the dead wood of trees. I was to come across a lot of these in the following weeks, and those here were identified for me by Liz Holden as being Armillaria cf borealis.

My first visit to the glen in September turned out to be a very good one, as I found a lot of interest there that day. Almost straightaway I spotted another harvestman (Mitopus morio), which is larger than the other species I’d seen earlier and the most common one in the forest. It was sitting motionless on a rosette gall on the tip of a branch of an eared willow (Salix aurita). This gall is induced by a midge (Rhabdophaga rosaria), and takes the form of a dense cluster of distorted leaves tightly packed into a rosette shape, within which the midge larva develops, safe from predators.

A few metres away some motion on the stone parapet of a bridge caught my eye, and when I looked more closely I saw that it was a wolf spider. In fact it was a female, and her sex was obvious because she was carrying a number of her spiderlings, or baby spiders, on her abdomen. Perhaps surprisingly, especially for people with an aversion to spiders, many arachnid species take great maternal care of their young, and wolf spiders all have the behaviour of the mother carrying the spiderlings for the first few days of their lives. Thanks to my friend Edward Milner, the spider recorder for Orkney and Shetland, I was able to get this one identified as being Pardosa lugubris.

While I was looking at the spider I noticed a brightly-coloured flowering plant in the daisy family at the base of the parapet. It was orange hawkweed (Pilosella aurantiaca), which is also known as fox and cubs, and I could see that it had aphids feeding on the top of the stem, just under the flower heads.

This is a plant I’m not very familiar with, and I’d never come across it with aphids feeding on it before, so I spent some time observing and photographing the aphids. Bob Dransfield identified them for me as being currant-lettuce aphids (Nasonovia ribisnigri), a species which alternates between two different hosts each season. It overwinters on blackcurrant or gooseberry bushes, where young aphids feed after hatching in spring. When winged aphids appear in early summer they migrate to lettuce plants and other members of the daisy family, including orange hawkweed, where they feed until autumn, when a new generation of winged aphids migrate back to their winter hosts. This behaviour of utilising two completely different host plants during an annual cycle is characteristic of many different species of aphids.

There is an old oak tree (Quercus petraea) growing beside this bridge with the parapet, and I’ve often made interesting discoveries by looking at it. This day was no exception, as I noticed a tiny beetle on the underside of one of its leaves, which looked different to any I’d seen before. Sholto Holdsworth identified it as being a species called Corticarina similata, which he said is probably under-recorded but is likely to be widespread. When I checked the NBN Atlas for it, I discovered there’s only one record there for it in Scotland, from the Cairngorms National Park, so this is possibly the first time it has been found in Glen Affric.

On the underside of another leaf of the oak, I found a spider and when I examined it, I noticed it had a white oval shape protruding from its body. I recognised this as being the larva of a parasitoid wasp, and thanks to the expertise of Mark Shaw I was able to get it identified as being a species called Zatypota percontatoria. This wasp occurs throughout northern latitudes, specialising in parasitising spiders of the Theridiidae family. The larva controls the spider’s behaviour as it grows, making it spin a web within which the larva can pupate, killing and eating the spider when the web is complete. Further information about this wasp is available here.

Moving on from the oak tree and further into the glen, I stopped to look at some golden-scaled male ferns (Dryopteris affinis) that were growing beside the road. By this time of year their sori (the structures on the underside of their fronds that contain the spores they use for reproduction) are ripe, and I found several fronds that were covered in them, so I spent a little while taking some photographs there.

The sori make beautiful patterns on the fronds, and provide a colourful contrast to the green colour of the rest of the fern.

Not far away, I  came across some pea galls on a dead leaf that was still attached to the dog rose (Rosa canina) it had grown on. These are induced by a wasp – probably Diplolepis nervosa (although there is a closely-related species, Diplolepis eglanteriae, that induces similar galls on dog rose, but there are few records for it in Scotland). I wasn’t able to confirm the exact species, as it’s necessary to rear the adult wasp from the larva inside the gall to make a definitive identification. Another related wasp (Diplolepis rosae) is responsible for inducing the robin’s pincushion galls on dog rose – one of the most spectacular galls of all – but I’ve never seen that in Glen Affric, although it has been recorded in the vicinity of Inverness.

There were plenty of fungi fruiting by this time, and I photographed a number of common species during the day. One of those was the angel wings fungus (Pleurocybella porrigens) , which grows on well-rotted wood of conifers – here it was on an old Scots pine (Pinus sylvestris) log.

Another common species that was very abundant this year was the fly agaric (Amanita muscaria). It seemed to be a particularly good year for them, and large groups were visible in many areas, always close to birch trees (Betula spp.). This is because the fungus has a mycorrhizal relationship with birches, in which the fungal hyphae wrap around the trees’ roots, and an exchange of nutrients takes place between them. In this mutualistic, or symbiotic, relationship the tree passes sugars it has photosynthesised to the fungus, while the fungus provides mineral nutrients from the soil to the tree. This partnership is fundamental to the wellbeing and health of the Caledonian Forest (and indeed to forests all over the world), but it is invisible for most of the year and only becomes apparent in autumn when the fungi fruit on the forest floor.

A week later I was back in Affric again, and although I visited the same parts of the glen as on my previous visit, as so often happens I came across a completely different range of organisms. The first of those was a black-kneed capsid bug (Blepharidopterus angulatus) that was on the leaf of a hazel (Corylus avellana). This is a common species that was identified for me by Joe Botting, a specialist in true bugs or Hemiptera, and it preys on small invertebrates such as aphids and mites, and also feeds on aphid honeydew.

On a different hazel I found another member of the Hemiptera, in this case one of the shield bugs – the parent bug (Elasmucha grisea). It was an adult that had newly pupated from a final instar nymph, and which would overwinter before mating next spring.

The hazel was also ready for next spring, as the buds for the male catkins that open in February or March, well before the leaves appear, were already fully formed.

Nearby, an unusual shape caught my eye on another hazel leaf, and when I looked closely at it I recognised it as being a globular springtail. Springtails (or Collembola, to use their scientific name) are not insects, but are a separate type of hexapod (meaning six-legged) invertebrate that are differentiated from insects by having internal mouthparts. I hadn’t seen this species before, but it was identified for me from my photos by Peter Shaw, whom I had commissioned to carry out a springtail survey at Dundreggan some years ago.

Peter had recorded this species at Dundreggan during his survey, but that appears to be only record for it in northern Scotland, so I was pleased to have found it in Glen Affric – it’s another addition to the list of species occurring there. Springtails get their common name from a specialised tail-like appendage called a furcula  underneath the end of their abdomen. This functions like a folded spring, and when the springtail feels threatened the tension is released, propelling it a considerable distance (relative to its body size) to escape from potential predators.

Hazels do not support as many species of invertebrates as some other trees such as oak and willow, but I continued to find lots of interest on them on this day. Just a couple of metres away from the springtail I noticed a strange shape moving on one of the tree’s small stems. Looking closer I saw it was a lacewing larva, with a lot of debris on top of it, crawling along the stem. I’ve seen this phenomenon before in other forest areas in the Highlands, but this was the first time I’d observed it in Glen Affric.

Lacewing larvae are voracious predators, feeding on other insects such as aphids, and some species like this one (which is in the Chrysopidae family, but I haven’t been able to get it identified yet) flick the bodies of their victims on to their backs, where they get caught on the larva’s bristles and form a remarkable natural camouflage. This helps to protect the larva from being seen by insectivorous birds etc.

Moving on from the hazels, I passed an alder tree that had lots of galls on its leaves. These are induced by a mite (Eriophyes laevis inangulis) and are quite common – some leaves can have dozens of them on their upper surface. The galls are raised up off the leaf on small stalks and are roughly spherical in shape. When they first develop they are yellow in colour, becoming green, then red and finally dark brown or purple as the season progresses.

The larvae of the mite develop inside the gall, where they are safe from predators. It is still a mystery how a tiny mite like this causes the alder tree to produce these remarkable shapes, but it is thought to involve the secretion of a special chemical. Under that influence, the alder grows this enclosed chamber for the mite larvae, and also provides special nutritive tissue for them to feed on. For me, it’s hard to fully grasp and appreciate the evolutionary pressures and timescales that must have been involved to create such a dramatic and unusual relationship.

A little further on I came across an eared willow (Salix aurita) that had some blackened sections on quite a few of its leaves. The black parts were fringed with orange, which formed a narrow strip between them and the normal, green-coloured part of the leaves. This indicated the presence of the willow tarspot fungus (Rhytisma salicinum), a species which is quite common and infects a number of willows, including the goat willow (Salix caprea).

Not long after that I reached one of the goat willows that grow in this part of the glen, and some of its leaves also bore evidence of fungal infection, in the form of small orange spots on their upper surfaces. These are caused by a rust fungus (Melampsora sp.). There are a number of species in this fungal genus that affect willows, and this one could have been either Melampsora caprearum or another species – it’s not possible to identify them just from casual observations like this.

The main part of the fungus is on the undersides of the leaves, and turning them over reveals a mass of bright orange fuzzy shapes scattered across the leaf blade. These are most apparent on damp or wet days – in dry conditions the fungus shrivels up and is much paler, as a result of desiccation. Interestingly enough, there are a couple of larvae visible in this photo here, although they are hard to spot, because their colour matches that of the fungus almost exactly.

These are the larvae of a midge (Mycodiplosis sp.), and they are more clearly visible in this photograph. They specialise in feeding on rust fungi, both in the genus Melampsora and others such as Puccinia and Phragmidium, which also produce orange growths on plant leaves. There are a number of different species of these midges, which are non-biting, and their larvae are all orange in colour like this – another example of the evolution of camouflage in Nature.

Cryptic colouration, as camouflage is referred to in more scientific terms, was becoming a theme of my day, especially when I came across one of my favourite examples of it when I reached Dog Falls. There are some aspen trees (Populus tremula) growing there, and I often check their leaves for signs of some of the many invertebrates that feed on them. On one I found an almost fully grown larva of the poplar hawkmoth (Laothoe populi) munching away on a leaf. This is a truly spectacular caterpillar, reaching a length of 7 cm., and it has a pattern of stripes and spots on its body that almost perfectly mimics the surface pattern and veins of the leaves that it feeds on. It even has a distinctive horn at the end of its body that closely resembles the petiole, or stem, of the leaf.

I remember being astonished and delighted when I came across one of these caterpillars for the first time, many years ago, on this very same group of aspen trees at Dog Falls. I could hardly believe my eyes then, that it matched the colour and pattern of the leaf so well, and it left me feeling exhilarated and in true awe of Nature for the rest of that day. What a wonder of evolution to have produced such a convincing example of mimicry in the form and colouration of this caterpillar! Because of its size, a larva like this would be a great meal for a bird, and its cryptic disguise is what helps it to survive. For any birds that do spot it, the caterpillar has another defensive mechanism to protect itself. When it is threatened up close, it rears its front end up, showing its rather fierce looking head and the three pairs of true legs, which look like sharp bird claws, thereby discouraging a predator from striking it.

My final discovery of the day came a bit later, when I was on the north shore of Loch Beinn a’ Mheadhoin. I was looking at some young Scots pines not far from the water’s edge when I noticed a number of wood ants on one of the branches. This immediately drew my attention as the presence of ants like this usually indicates there are aphids feeding on the tree. The ants tend the aphids, helping to protect them from predators and parasites, and also feed on the liquid waste product, known as honeydew, that the aphids secrete.

Sure enough, as soon as I looked closely at where the ants were, I could see lots of aphids feeding, mainly on the underside of a young branch of the pine. I recognised also that they were a different species of aphid to those that I had found earlier in the summer on the ‘champion’ Scots pine in the Coille Ruigh na Cuileige exclosure that featured in Part 2 of this blog. Whereas those ones – the large pine aphid (Cinara pinea) – had been few in number, but large in size (at least as far as aphids are concerned!), these ones were smaller and in a dense concentration, feeding together on the underside of the pine branch.

At home that evening, I was able to identify them as the Scots pine aphid (Cinara pini) by referring to the excellent Influential Points website, which is run by Bob Dransfield and Bob Brightwell. Apparently the aphids’ behaviour of feeding on the underside of branches is common in the latter part of the year – perhaps this is to make them less visible to potential predators at a time when their protective wood ants are less active, because of colder weather?

I spent a while watching the wood ants moving back and forth amongst the aphids, stroking them with their antennae to stimulate the production of honeydew, which is a major food source for the ants. Thanks to the expertise of Hayley Wiswell, I was able to get the ants identified as being the northern or hairy wood ant (Formica lugubris), which is the commonest species of wood ant in Glen Affric.

I hadn’t come across this species of aphid in Glen Affric before, and it made a fitting end for what had been another day of interesting discoveries. I made a note of the location of this Scots pine, as I planned to return to it in the following weeks, to see how long the aphids stayed there, before they disappeared with the onset of colder weather and shorter days. What I found then will feature in Part 4 of this blog, along with a lot other interesting discoveries I made in the final months of 2018.