Tag Archives: Gunnersbury Triangle Nature Reserve

Conservation, Natural History, Nature Reserves

Giant Ichneumon in London Reserve

15 May 2014 Ian Alexander

A terrifying monster stalks the suburbs. Silently and with unerring accuracy, it scans the surface, using its advanced sensors to detect and identify targets buried deep below. Once a target has been located, the hunter drills down to find it, deposits the payload, and leaves in search of the next. It could be a cyber-borg or pilotless military vehicle. Actually, it’s Rhyssa persuasoria, the giant Ichneumon. And giant or not, it’s about 30mm long.

Rhyssa is a parasitic wasp, a solitary hunter distantly related to the social, black-and-yellow striped wasps. Her prey are the larvae of other insects which burrow in dead wood for food and safety. Only when she is above, safety below is hard to find. For Rhyssa‘s weapon is as long as her body: her ovipositor is greatly elongated into a precision instrument that can drill deeply through wood and into the body of the larva. Once there, she lays a single egg down the ovipositor tube. The egg hatches inside the still-living larva, and devours it from the inside. The larva dies (so Rhyssa is a parasitoid, not a true parasite that avoids killing its host) and a young Ichneumon emerges.

Rhyssa persuasoria dorsal view — Rhyssa persuasoria, dorsal view: in search of a host

Today at Gunnersbury Triangle we erected a new bench, to allow visitors to relax and enjoy a quiet moment in nature. It sounds a trivial task. If only. Two volunteers spent a day putting the “ready to assemble” kits together. All the supplied bolts were the wrong size, so they had to ream out all the pre-drilled holes to the larger size. Meanwhile, that day, I dug out the well-embedded MetPosts remaining from a previous bench. Then we dug 2 holes for the new bench: they promptly filled up with water, and the deeper we dug, the more the local weakly-cemented gravel (our local rock, when it isn’t sticky clay) collapsed into the hole, making it wider at the bottom. It was clearly hopeless.

So today we spent an hour prospecting for a drier place that would also be aesthetically pleasing, not harm the rare ferns nor disturb the nesting Blackcaps, and be close to an existing path. Then we started digging holes all over again. This time they didn’t fill up with water, much: just the bottom 10 cm or so. To keep the sides from crumbling, we avoided digging with spades: we lay on bin-bags, and wearing rubberised gardening gloves, scooped out handfuls of wet gravel. Then we levelled the two holes, cast a base of PostCrete in each, let it cure — at this point everybody disappeared for a cup of tea, leaving me in the wood guarding the site. I sat on a coppiced Willow trunk, and was approached by the giant Ichneumon when I least expected it. Luckily my little camera was not far away — you can readily imagine why I wouldn’t want the big camera with me while working.

The team reassembled, we gingerly lowered the bolted wooden creation into place, wedged it tight with broken bricks, and fixed it in place with plentiful PostCrete before cunningly sloping the top to shed rainwater. Needless to say, during this procedure we accumulated more and more tools all round the excavation site. If only it were as simple as drilling for an unseen caterpillar and laying an egg in it. But then, Rhyssa has the jump on us, with millions of years of evolution in her hunting technique.

Conservation, Love of Nature, Nature Reserves

Yay! It’s Frog Day! Pond-dipping at Gunnersbury Triangle

11 May 2014 Ian Alexander

I try to get down to the pond on Frog Day because, whatever the weather, it’s always such fun looking into trays, seeing what people have caught, and helping people to get a rough idea of what sort of wildlife they are looking at. The parents too are frequently fired up with (especially boyish) enthusiasm. One dad turned out to be expert at catching newts; another family caught dozens of tadpoles (all still without legs).

People come and go; some are regulars, some are new, some were just passing by and are astonished to find a nature reserve here, let alone a pond and volunteers and free pond-dipping and wriggly wild animals.

And there definitely weren’t just the usual suspects in the water, either.

Budding Hydra, with head of a damselfly nymph — Budding Freshwater Hydra, with a nymph

This really was a surprise; a Hydra, not just bright green but actually budding. These tiny animals are coelenterates, like corals and jellyfish, with no proper gut running mouth-to-anus, but just a mouth surrounded by the tentacles, and a hollow bag of a body; anything undigested has to come out the way it went in. The animal is green with symbiotic algae, so it has quite a bit of plant about it, and when it isn’t in a white dish, it’s practically invisible.

This little fly has two tails, and may well be a Stonefly; it is a lot smaller than the common Mayflies, which have three tails. It seems like a special animal today.

A fine Dragonfly nymph was captured in one dish; here it is, being examined closely by one youngster. I saw a Broad-Bodied Chaser near the pond some years ago, so it might be that species.

With their characteristic three tails, the Mayfly nymphs are distinctive. Here in one dish are some, along with what seems to be a long slim beetle nymph, and the Dragonfly nymph. There were quite a few Damselfly nymphs about too, some quite boldly green.

At four we packed up to go and have a well-deserved cup of tea. As I turned round, I realised the Yellow Irises the other side of the boardwalk were in full bloom.

Natural History, Wildlife

Wood Wasp, Sprouting Loggeries

6 May 2014 Ian Alexander

While doing the Butterfly Transect at the Gunnersbury Triangle, I came across a fairly large Wood Wasp (in the sawfly family), about 25mm long. It was a bit tricky getting a photo, as these insects are distinctly skittish – they race about in the shadows, occasionally perching on a leaf’s upper surface. The breeze was wafting the branches gently, so patches of sunlight came and went. I shot several images with the miniature camera – it has two big advantages over my full-size SLR: one, it has a very short focal length, so it has a better depth of field than an expensive macro lens; two, it’s small and cheap, so I habitually carry it with me in my rucksack.

The two images here show (left) the resting position with the wings over the body, the long antennae, the alarming-looking ovipositor, and the orange-brown legs; and (right) the plump black abdomen with white spots. Perhaps the two images show that it’s rather hard to get a single image which is suitable for identification. This one looks like a Sirex so perhaps that’s what it is. The eggs are drilled into wood.

The butterfly transect yielded the first definite Green-Veined Whites, i.e. I was able to get close enough to be sure; until now they’ve all been “Small/Green-veined” worse luck. There were some Speckled Woods and an Orange Tip, too; a Brimstone turned up after I’d put the clipboard away.

But the most curious observation of the day was this sprouting loggery. We ‘planted’ (more literally than we knew) the sawn Willow logs in the winter. They seem very happy in their new setting and are growing vigorously. It will be interesting to see how they get on.

Natural History, Talks

Camouflage without Spots: Gunnersbury Triangle, Sunday 8 June 2014 at 2pm

25 April 2014 Ian Alexander

Cheetah (title image) — Camouflage without Spots: is that even possible?

Free Talk: Gunnersbury Triangle, Sunday 8 June 2014 at 2pm

In this short and I hope lively talk, illustrated with models and photographs, I will try to show that camouflage is a lot more than spotty coats.

Animals use many different tricks to hide themselves. Even when there is no cover to hide behind, animals find ingenious ways to make themselves invisible. And if they don’t need to hide, they use the same tricks in reverse to make themselves as obvious as possible.

“Suitable for ages 8 – 80”. Roughly.

OK, you want more technical detail. Hmm. Well, I shall not be talking about military camouflage, though it is (or should be) based on the same principles as in zoology. The title already promises no spots, more or less, so I shall obviously mostly be avoiding what my hero Hugh Cott called disruptive patterns. Yes, you can see that I’ve spent far too much time trying to improve Wikipedia’s coverage of camouflage. If you nose about in there you’ll discover that I’ll have plenty of spotless methods to talk about. To whet your appetite, here’s Hugh Cott’s beautiful drawing of a Potoo, which makes itself as good as invisible by perching, stone-still, atop a broken branch. I’ll leave it up to you to work out how the trick works. Even better, come along to my talk.

Hugh Cott's Invisible Potoo — Hugh Cott’s Invisible Potoo

Conservation

Hunt that Frog

3 April 2014 Ian Alexander

Down at the reserve, it was time to strim the meadow, which meant a frog hunt. A conservation frog hunt, to dislodge any frogs that might otherwise get permanently strimmed. I walked up and down, sweeping through the cow parsley – it’s a major reason why cutting is now necessary, it needs to be held back to allow more delicate flowers like garlic mustard through – but no frogs hopped out. I looked under the mats placed there for amphibia – there were no frogs, just three small toads sheltering in the cool darkness.

On the woodland edge of the meadow, brambles have been spreading in their looping way, bending down to the ground, striking root and springing off another few feet into the grass. I pulled up some dozens of them, cutting roots where necessary to leave nothing that could regrow. Some people just quickly clip them off above the ground, which slows them down for a little while: pulling, digging or root-clipping is far more effective.

Down at the pond, the heron was waiting silently, watching for frogs to eat. Since it has arrived, frogs have been much harder to find. I wonder how many of the dozen large frogs I saw mating a few weeks ago have finished up in that enormous dagger-shaped beak.

Natural History, Nature Reserves, Wildlife

Spring has sprung

1 April 2014 Ian Alexander

Today dawned foggy and cool, but the sun soon burnt its way through and it became a hot spring day. I spent most of it reroofing the tool shed at the Gunnersbury Triangle nature reserve. It was in tatters after at least one hard winter, and it was an interesting exercise peeling off the layers hopefully tacked one on top of the leaky other. I then removed three full boards from the roof, complete with what I’m sure any mycologist would have found a fascinating colony of wet rot fungus, together with several wriggly centipedes and a lot of woodlice.

As it grew hotter on the roof, I was joined by at least two species of hoverfly, one large, dark, and almost unstriped. A brimstone butterfly chased around with a smaller white, perhaps a green-veined or an orange tip. A comma butterfly wandered about. Down below, the stinging nettles, hops, and garlic mustard (ideal for orange tips) are coming up nicely, but there’s too much cow parsley and some volunteers are pulling a lot of it out.

At lunchtime I walked down to the pond. Chiffchaffs were singing all over; the pond was suddenly covered in pond skaters (Gerris) with one or two whirligig beetles. The tadpoles have hatched out into a wriggling mass.
Spring has sprung.

Conservation, Nature Reserves, Wildlife

On the boardwalk, we’re havin’ some fun

27 March 2014 Ian Alexander

Since rain was forecast, we drank up our morning tea quickly, took the tools we needed and wheeled our wheelbarrows off into the reserve. I was given the job of making the boardwalk over the pond safe. It looked all right, but quite a few boards were springy, one or two wobbled, and there were some alarmingly wide gaps where the boards fanned out to get around an angle, so they were tight one side, gappy the other. A mallard duck and drake were snoozing on the other end of the boardwalk. She had laid an egg in the swamp, then moved it behind a tree, but didn’t seem to be sitting on it.

I’m not particularly keen on power tools, but the volunteer officer gave me some flattery about my always doing work aesthetically, so I took a look at the boards. Sure enough, at the angle the boards were all over the place, uneven, and fixed any which way. A chiffchaff sang its endless, two-note ditty: not all warblers have thrilling, nightingale-like songs.

I took the drill and set about pulling out the worst of the boards. Three screws came out; the fourth one was inaccessibly deep and the drill bit just rattled over it. I jemmied up the board, hammered out the offending screw from the back, and levered it off. This was not at all the quiet and restful day in nature I’d had in mind. I lined the board up where I felt it should have gone and screwed it down. The next gap was now wider than before, so it was the next board’s turn. You can guess where this was going. On the fourth board I pulled out six screws, but it still didn’t budge. Scraping around carefully, I spotted another screw, deeply buried in a dirty crevice. I cleaned it off as best I could and luckily it came out. The board was still remarkably solid at both ends: clearly there were still at least two screws holding it down. But where? I took a spare screw and scratched about suspiciously: sure enough, there were two more subtly buried heads. I picked the mud out of the heads, and remarkably they both came up with the drill. Nine screws where three or so should have sufficed, on a misplaced, unchecked board.
Just as I was fixing it down with these dark thoughts, a blackcap burst into song: the first of the year for me.

The remaining planks were not too gappy, but were a bit higgledy-piggledy at either end. I pulled up a few more and lined them up to step round the angle as evenly as possible. Then I walked about and put in a line of screws where the boards were springing up and hadn’t been fixed down to the stringer below. The sun was shining and it was really quite warm on the boards. Suddenly there was a splash, and a lot of quacking. A rival drake had landed on the pond! The sleeping pair stood up and quacked for all they were worth. In a moment he had come over, and the pair jumped into the pond. He gave chase. Round and round they went, taking shelter under my feet, their position given away by a steady line of ripples. Then out they burst, flying, splashing down, sometimes with both males grabbing the female. They all flew off, but came back to fight some more a few minutes later. Being a drake in the breeding season is clearly hard work, even when you’re the only resident on a pond.

Nature Reserves

Singing in the rain

26 March 2014 Ian Alexander

Even as I arrived the weather looked threatening. The sun sparkled dramatically off the water, under a magnificently dark cloud, making the marsh marigolds gleam golden against the almost-black water.

From the hide, redshanks could be seen scurrying about; some lapwings energetically chased off a few carrion crows, and a few snipe wandered about, right out in the open, ceaselessly probing the mud for food. Even better, the first little ringed plover of the year came out on to the marsh, flying off suddenly, its narrow wings flashing. The lapwings’ territoriality is valuable to other nesting birds, like the little ringed plover, as it protects their nests from predators of eggs and young like the crows. Lose the lapwings, as we have done across most of England – there are hardly any wet meadows left – and you lose much more. Drain and fertilise the meadows, and coarse grasses outgrow all the delicate flowers: you lose both the beauty and the bees, and the bees matter as they pollinate crops. The farmers hardly noticed they had done anything: after all, they only did a few sensible things to the land. That’s how delicate the ecological balance is.

The rain arrived, sweeping in on a cold wind that whistled through the hide windows, spattered camera lenses and binoculars with fat raindrops. In a minute, every window was closed, everyone happy to be in a warm dry place. I focused the telescope on a snipe and watched it while the rain threw up splashes all around it. Every minute or two it shook itself, keeping its feathers dry and fluffed up to maintain its insulation – clearly its plumage is nowhere near as oily and waterproof as a duck’s. But it went on feeding, its legs in the chilly water, its long beak in the mud, or retracted and rapidly opening and closing as it swallowed its catch. Living and feeding on a marsh means being cold and wet most of the year, really.

In the distance on the open water, three or four newly arrived sand martins swooped to catch insects from the surface, dashing about like the tiny brown tailless swallows that they are – I was watching them through the telescope (not something that often works well with fast birds like swallows), gently swinging from side to side to follow them as those watching with binoculars tried to count how many there were, little fastmoving specks against the water. We were all enjoying some wildlife, small as matchboxes, over a hundred metres away, flying in the rain. It was a very light, happy atmosphere in the hide, with nobody in a hurry, all the talk on the birds we could just about see. Really, it was perfect.

Conservation, Wildlife

Not much to see at this time of year?

11 March 2014 Ian Alexander

After the brief heatwave it feels like March again. In the Gunnersbury Triangle nature reserve, willow buds are starting to open but only the evergreen trees like the native yew and holly, and the invasive holm oak (from the Mediterranean) are in leaf. Not much to see, then? Not a bit of it.

In the leaf litter under the forest canopy, a large and handsome white slime mould was spread out, draped over some twigs in a fine shiny film. In detail its surface seems almost fractal, full of rounded holes at different scales like a Sierpinski Triangle if you know what one of those is. The individual cells – I’d almost call them animals – of the slime mould signal to each other with a chemical (AMP), which causes them to aggregate; they slowly ooze along like amoebae, eventually forming fruiting bodies rather like small fungi. It’s an extraordinary process, and in an odd way quite beautiful.

Leaf Miner, probably Ectoedemia heringiella on Holm Oak

Meanwhile, the large holm oak by the picnic meadow looks utterly extraordinary, something like the horse chestnuts that have been attacked by plagues of leaf miner moths. Almost every leaf of the holm oak is scarred yellow and brown with the wandering trails of the moth caterpillars, making the tree look multicoloured and very badly battered. This is probably the work of Ectoedemia heringiella, according to the RHS.

A filzgall, Aceria ilicis, on Holm Oak leaf

Many of the leaves also have squarish brown furry patches (a filzgall or erineum ) on the underside; the leaves are naturally fluffy, with a tiny gall mite, Aceria ilicis, causing overgrowth; the thickened, darker hairs are too tough for the insect to eat, so the plant’s reaction works as a defence.

And that is not all; there are also a fair number of much larger pupae, probably of another moth species, wrapped in partly-rolled leaves, tied up with silk threads. We used to think of the holm oak as a useless non-native species with no pests or predators: not any longer, it seems, though at least the leaf-miner is a recent arrival itself.

Down at the pond, there are masses of frogspawn; at least a dozen large frogs, with at least four mating pairs, were responsible. When we came over the mound they must have seen us as there was a remarkable amount of splashing; even in amplexus they are capable of emergency diving: this is just as well, as much of the weed and reed has been cut during the winter.

Conservation, Wildlife

What are we conserving?

24 February 2014 Ian Alexander

: Kings Cross Development looms over Camley Street’s new Viewpoint

Everyone in the packed council chamber turned to look at the chairman of the planning committee. The members had voted 6-6: a tie. “As chair with the casting vote, I am voting for the development.” There was stunned silence. The developers said nothing. We objectors took a deep breath and said nothing. Gunnersbury Triangle Nature Reserve would never be the same again.

London Wildlife Trust’s other central London reserve at Camley Street is also changing. A 10 storey block has cut off the view. Were all our reserves being trashed? Were we fighting for nothing? 30 years ago a passionate campaign saved the Gunnersbury Triangle from becoming four industrial units. Miraculously, with a huge input of volunteer effort, it became a wet woodland with little meadows, grassy banks, leafy paths, a handy pond for school pond-dipping. Now it’s surrounded by 4, 6, 8-storey buildings. The latest one at Colonial Drive is right up against the reserve boundary — at the top of a ten-foot bank. The quiet meadow and scrubby corner where the whitethroats nested will be illuminated 24 hours a day by stray lamps from a wall of flats. “I’m desperately saddened at the insensitive nature of the development — it robs local people of the sense of countryside,” says long- time campaigner and Gunnersbury Triangle committee member Jan Hewlett.

Certainly, the reserves will feel different. But Camley Street has a new ‘Viewpoint’, an architect-designed floating open-air classroom. It will be beautiful to sit and learn on the canal, in the little watery oasis in the midst of the busy city. At Gunnersbury Triangle, too, the blackcaps and thrushes will delight our hearts in springtime. School groups will still lie down on the boardwalk we built and enjoy catching newts, dragonfly larvae and ramshorn pond snails.

Our reserves must change with our great city. They do not feel like forgotten corners of countryside any more. They are little oases, islands in a sea of noise and pollution and traffic. They are special exactly because they are right in the heart of our vibrant capital city.

ObsessedByNature