Saturday, March 28, 2009
Chomping its way through a fallen twig, photo 1 shows a collection of the 'candle wick-like' fruiting bodies of the Candlesnuff fugus Xylaria hypoxylon.
This fungus is very common here in the UK. Scan piles of logs or fallen branches and you're likely to spot it on almost any country walk.
In common with the holly leaf fungus I blogged recently, and the morel before that, X.hypoxylon is a member of the ascomycetae - a huge collection (phylum) of fungi that 'grow' their spores inside microscopic tubes called asci.
In the case of X. hypoxylon a couple of hunded asci are, in turn, packaged into a structure called a perithecium - basically a small 'pimple' with a hole in the top through which spores, once liberated from an ascus, escape. There's an excellent cross sectional microscope photograph of a perithecium of one on the mycolog site (it's a big webpage - the photo's about half way down).
To the eye, the perithecia of X.hypoxylon appear as tiny black pimples on the surface of the white 'candle wicks'. You can see some in photo 2. (Perithecia are common features of lichens also (see my post here).) Over time, the surface tends to become increasingly covered with these pimples (compare Photo 1 with Photo 3 taken about two weeks later) until finally the 'wick' ('compound ascoma') appears quite black. The resulting 'charred' look gives the name pyrenomycetes (from the Greek 'pyr' = fire) to the class of mushrooms of which X.hypoxylon is a member.
The definitive web site on the pyrenomycota is that of by J.D. Rodgers.
In fact the life cycle of X.hypoxylon is a little complex. The spores liberated by the pimply black perithecia are the result of sexual reproduction. X. hypoxylon is also able to reproduce asexually via so-called 'condiospores' however. These conidiospores give the fungus its white powdery appearance in photo 1.
Seen under the microscope, the sexual spores of different species of mushroom show characterisitic differences in size and shape (a helpful aid when trying to identify a mushroom - see my previous posting). I read on Michael Kuo's site however, that conidiospores from different fungi all look basically the same. Why nature has chosen to distinguish sexual and asexual spores in this fashion I can't imagine. Can anyone comment?
Tuesday, March 24, 2009
Spring is well and truly springing here in Oxfordshire. Soon animals and plants will be appearing in my garden faster than I can photograph them, let alone write about them. Whilst things are still moderately calm therefore, I'm seizing the moment to press on with my task of cataloguing my garden's lichens.
Quietly going about its business, photo 1 (click on photos to enlage) shows a black crustose lichen (for the uninitiated, see my explanation here) that decorates my garden wall in places. Photo 2 is a closeup (I've slightly digitally sharpened this image using software).
I'm no expert, and happy to be corrected, but from what I can tell from leafing through my copy of Lichens (Frank Doson), although there are numerous lichens with black fruiting bodies ('apothecia') on otherwise coloured 'backgrounds' ('thalli'), there are only a handful of mostly- or wholly-black crustose lichens to be found in Britain. A number are marine. Verrucaria maura, for example, is common on rocky shorelines where it is somtimes mistaken for oil pollution.
Of the mostly black, 'land-locked', lichens, I spent some time looking at the photos of Verrucaria nigrescens on the excellent 'UK Lichens' site. Looking closely however, this seems to have a more chocolate-brown thallus, albeit one peppered with many black 'perithecia' (see my definition here).
On balance therefore I'm tentatively identifying my lichen as Placynthium nigrum which my copy of Dobson describes as being "Very common, mainly on hard calcareous substrates throughout Britain. Often found on flat tombstones and cement".
A slight puzzle is that the photo in Dobson shows a more powdery ('coralloid') surface than is evident in my photo 2, although the book adds this lichen may be "sometimes smooth and cracked especially in polluted areas". Where I live is rural and I don't believe especially polluted. That said, some lichens are extraordinarily sensitive to even minute amounts of air pollution - whole books have been written on this topic. Anyhow this variability in texture gives me some added confidence in my identification.
Turning to my copy of Lichens (Oliver Gilbert, New Naturalist Library) a nice thing to discover was some growth-rate data for Placynthium nigrum. I learn that young patches expand their radius at 1.66mm/year and mature patches at 0.08mm/year. Lichenometry is the technique of dating old structures (churches, stone circles etc.) by studying their lichen populations - you can find an article here. Applying the data above to the approximately circular, 10mm-radius, patch in photo 2 ages my lichen at between 6- and 125-years old! Not the most exact figure I grant you, but fun to know.
As I commented in a recent posting, I am puzzled by the colours lichens adopt. Over the millenia animals have been driven to evolve their numerously-coloured fur coats, feathers and exoskeletons so as to optimally attract mates, hide from predators, advertise their venomous stings etc. Similarly my amateur's understanding is that plants are mostly green by virtue of the need to pack their leaves and stems with chlorophyll. Even various of the larger mushrooms have evolved specific colours, presumably to alert browsers to their poisonous nature or advertise their presence to 'pollinating' (botanists may wish to turn away at this point!) insects. Some even glow in the dark for this very purpose. But how it is that some lichens on my garden stonework gain advanatage by being coloured matt black, whilst others 'prefer' greyish/white and still others, bright yellow, I struggle to guess. Can anyone help?
Today's posting brings my garden lichen species-count to eight. I feels that I may be approaching completion with regard to this particular lifeform. Until, that is, I find another dozen species through more careful inspection of my garden's rocks and trees. Stood outside earlier today for example, when acquiring the photos above I was aware only of our black friend and of the grey-white patches which (though I haven't checked in detail) I'm assuming is our old friend Verrucaria. Sitting now at my computer screen however, staring at an enlarged version of the photo 1, I'm suddenly noticing the array of tiny orange blobs towards the centre of the image. Time to go back outside methinks!
Hot on the heels of one of my favourite garden birds, one of my favourite flowers: The Snowdrop (the photo was taken back in mid-February)
Snowdrops are members of the plant genus Galanthus (from the Greek 'gala'=milk, 'anthus' = flower). What I've learnt about them has been mostly through Mark Smyth's very nice Snowdropinfo website, the Royal Horticultural site, the BBC site, and from my trusty copy of The Englishman's Flora (Geoffrey Grigson).
Firstly, regarding the name, both the RHS site and Grigson state that 'Snowdrop' derives from the German word Schneetropfen, a type of ear ring popular in the 16th and 17th century. Now, whilst I'm entirely happy to accept this, neither author gives a reference without which it's not immediately obvious to me that likening this plant to a 16th century German earring is more likely than people having chosen the 'Snowdrop' after... er, well...drops of snow! (Anyone?)
Geoffrey Grigson lists other folk names including Eve's Tears and Candelmas Bells, the latter a reference to the Christian festival of February 2nd when Snowdrops are one of the few plants in flower.
According to the BBC's site, bringing Snowdrops into the house at Candelmas symbolises a death.
Snowdrops are widely spread across Europe and Asia. There are nineteen true species (there's a list on Wikipedia's Snowdrop page) and literally hundreds of artificial cultivars, with new ones created all the time by enthusiasts ("Galanthophiles"), and old varieties occasionally re-discovered in sleepy vicarage gardens or (see the National Trust site here) on overgrown Victorian rubbish dumps!
You can find a photo-gallery of cultivars on Mark Smyth's site. What characteristics elevate nineteen types of Snowdrop to true species level I'm not sure (anyone?). My copy of 'The Wildflower Key' (Francis Rose) lists only one for the UK - Galanthus nivalis.
The chemical Galantamine was first isolated from Snowdrops and today finds medical application in the treatment of Alzeimer's disease.
Finally a few words on Snowdrop pests and diseases, of which there are various: The RHS site describes the two fungi Botrytis galanthinae and Stagonospora curtisii as 'the bane of many snowdrop growers.' Snowdrops are also attacked by the larvae of the Swift Moth and the stem nematode worm (Ditylenchus dipsaci) (you can download a pdf file about the latter here). Prize for impressive pest has to go to the Narcissus fly (Merodon equestris) however. This black-and-yellow insect wards off predators by mimicking a Bumblebee. You can find some photo's at the insect images website. Painful as it will be to the ears of gardeners, and although I enjoy my garden's snowdrops far too much to want to see them all wiped out, as an amateur naturalist I have to say I wouldn't mind sacrificing just one or two bulbs for the chance to see one of these flies for myself!
Monday, March 23, 2009
I promise that shortly I will end my minor obsession with moth postings dear readers and return to describing some of my garden's other life. For now however, two more moths caught in my new home-built moth trap.
Photo 1 shows an Early Grey (Xylocampa areola), its wings camouflaged to help it hide on trees and, photo 2, a rather tired and tattered looking moth that I think may be a Dark Chestnut (Conistra ligula) though is possibly a Chestnut (Conistra vaccinii) (My identifications come with a ‘health warning’ - I’m no moth expert and happy to be corrected). You can find better photo's on the excellent UK Moth site.
Caterpillars of the Early Grey feed on Honeysuckle, and those of the Dark Chestnut on Willow and other plants.
I learn from my copy of Moths (Michael Majerus) that the Dark Chestnut is an unusually early egg-layer amongst British moths, usually laying in March.
Sadly, beyond the facts above, I’ve been able to find very little to say about the life-styles and behaviours of either of my moths. Of course, this may be because I’ve not searched enough. If there is one thing that I have learnt from writing this blog however, it won't be because there is nothing remarkable to discover about them. As I've discovered time and again during my researches, there is an almost inexhaustible subtly and complexity in nature.
Take for example, the two butterflies, The Grayling (Eumenis semele) and the European Silver Washed Fritillary (Argynnis paphia) -
In his semi-autobiographical Curious Naturalists, a wonderfully readable account of a life spent watching and recording behaviour in birds and insects, and one of my all-time favourite natural history books incidentally, the Nobel Prize winning biologist Niko Tinbergen described some of the 50,000(!) experiments he and his team performed to gain an understanding of the behaviour of the former butterfly.
During the breeding season, male Graylings are in the habit of chasing almost anything that flutters by in the hope it may be a female. Using equipment no more sophisticated than a fishing rod 'baited' with a series of cut-out paper shapes, Tinbergen was able to reveal such facts as i) Although male Graylings are sensitive to colour (they preferentially feed on blue and yellow flowers) surprisingly, when choosing to give chase, they don't care about the colour the object fluttering by ii) Nor are they the least concerned that the ‘flutterer’ should resemble a fellow butterfly – they will happily chase a fluttering paper rectangle iii) They do care about size however; If you’re a male Grayling seeking a mate then, within reason, the bigger she is the better!
This is only the start. Once a male finally meets a female, a rich and complex courtship ‘dance’ ensues with he performing acts such as wafting scent over his partner with his wings, and gently clasping her antennae between them.
Now, in her book, Courtship: A Zoological Study (publ. Heinemann), Dr. Margaret Bastock describes some similar studies (made by D. Magnus in the 1950's) into the breeding rituals of the Silver Fritillary. Again males will chase a variety of passing ‘fluttery things’, but this time males are choosy about colour -they like best to chase yellow things.
Two butterflies, two rich and complex behaviours with intriguing differences, both only ‘decoded’ by thousands of hours of patient observation. It makes me wonder what intricate shenanigans my two moths may be about in the dead of night. (Anyone?).
Even supposing more is known about my two moths however, with more than 850 larger moths in the UK alone, not to mention 250 hoverflies, more than 450 spiders, 3200 Ichneumenoid wasps…and let’s not even think about beetles (see here), it’s certain that only a tiny fraction of what goes on in the gardens, fields and forests on our doorsteps is known in any detail.
Personally I find it both an inspirational ‘call to arms’ to we amateur naturalists to get out our notebooks and our ‘paper butterfly' experiments, but also (if you’ll permit me a slightly gloomy ending to today’s posting) a little sad to think that in one’s lifetime there will never be enough time to observe even a small part of what there is.
Saturday, March 21, 2009
In my last posting I described my newly home-built moth trap. I’ve been operating it for only a week, and although we’re still in chilly-March here in Oxfordshire in the U.K., I’ve already ‘discovered’ a further half dozen species to add to the seventy-five living things I’ve already reported on this blog. Normally I give each species its own posting. I’m beginning to think however, not least with summer’s ‘bounteous harvest’ approaching, that it’s likely I’ll find so many night- flying insects I’m going to need to relax this rule if I’m to stand any chance of cataloguing my garden life in a realistic time frame.
Why is it that some - although interestingly, by no means all- species of moth are attracted to artificial light? The late, great moth expert Professor Michael Majerus had a wonderfully concise answer in his book Moths (The New Naturalist Library):
“I do not know”!
A common hypothesis is that moths, some of which navigate by the distant moon and stars, are fooled into trying to navigate by the artificial light. Possibly this is the answer, but if true you might reasonably expect to see moths approaching lamps in a navigational fashion via orbital, in-spiralling flight paths. Watch a moth approach a light trap however, and I have to agree with Majerus, it’s not easy to convince yourself you’re witnessing 'navigation-in-action'. Moths often fly directly towards the light, flutter around it in seemingly haphazard ways, or seem content to settle some distance from it.
Hsaio has put forward (Jour. of Insect Physiology, Vol. 19:1971-76, 1973) an alternative theory that point light sources ‘interfere’ with the operation of moths’ compound eyes causing them to perceive regions of darkness (i.e. good places to hide) around a lamp where there are none. Again, Majerus isn’t convinced. Another of nature’s mysteries! Maybe a reader here has a comment?
To the moths themselves: Firstly, attracted to my light about a week ago, the moth in photo 1. I struggled to identify this one at first, but then caught sight of a photo of The Yellow Horned (Achyla flavicornis), in a slim photo-guide (G.Hyde, British Moths, Jarrold Colour Publications) I’ve had since I was a boy. The larvae (you can find a photo on Ian Kimber's excellent UK Moths site) feed on Silver and Downy Birch from mid-May to July before pupating to over-winter and emerge as the adults found from late-February to mid-April. I read that the Yellow Horned is a member of the Thyatiridae family of moths represented by only nine species in the U.K.
On the same evening, photo 2, a March Moth (Alsophila aescularia), the green larvae of which (again, photo's available on Ian Kimber's site) feed on many broad leaf trees including Oak, Willow and Birch. The adults fly from late February to April and over-winter as a pupae. The March Moth is notable for being one of a small number of moth species where the female is flightless. You can find a photo of a wingless female here.
Why it is that a small number of moths can ‘get away’ with having no wings, whilst all the rest expend precious energy growing them is...yep you guessed it...another of mother nature’s mysteries...at least, it is to me. Comments anyone?
Monday, March 16, 2009
In my last posting on the Song Thrush I introduced my home-made camera 'trap' and mentioned that this gadget was one of a number I've been cobbling together:
Ladies and Gentlemen, a round of applause please for... (photo 1) ...the Skinner/Walloon Moth Trap!
One of a number of moth trap designs you'll find on the web, the principle of the Skinner trap is simple enough: A lamp to lure the critters towards a box fitted with a 'lid' comprising two sloping sheets of plastic that don't meet in the middle (leaving a gap of about ~1inch) . The moths flutter around the lamp, land on one of the slopes and slide into the box below, whence they aren't smart enough to find their way out. A few egg-boxes give them somewhere to hide.
To best attract moths you need a lamp that peaks towards the blue/ultra-violet. Best is a mercury vapour- or so-called actinic-bulb (you need the correct electronics (a 'ballast') to power either incidentally). I bought the various bits I needed from the Entomological Wildlife Group.
And the result?
Twenty minutes spent flicking through my copy of Moths (Waring and Townsend, British Wildlife publishing) and I'm confident I've met an Oak Beauty (Biston strateria).
The Oak Beauty is a member of the Geometridae family of moths of which there are some 20,000 known species with 300 occurring in the British Isles. Geometridae is from the same stem as geometer and is a reference to the measuring, 'inch-worm' gait of these moths in the larval stage. The caterpillars of the Oak Beauty feed on Oak, Hazel, Alder, Aspen, Elm and Sallow. They are well camouflaged to resemble twigs. I've never myself seen one, but you can find a photo of one here.
The moth I caught was a male, as indicated by his impressively large, feathery antennae (close up in photo 2). I personally find such structures a miracle of natural engineering.
Turning to my copy of the superb Moths by (the recently deceased) Michael Majerus (The New Naturalist Library), one thing I learn about the Oak Beauty is that it has a melanic form that occurs in Holland but not in Britain.
For those unfamiliar with melanism: Much as people can differ in their eye colour and yet all remain members of the same species (human'), so some moth species can show considerable variation in their wing pattern. Within one species, some individuals might have patterned wings whilst others might have, say, matt black wings. Careful studies over decades have shown that the places where moths with certain wing patterns predominate are those places where having e.g. black wings is a recipe for good camouflage from predators (say, birds).
The increased prevalence of black winged moths of the Oak Beauty's sister species, the Peppered Moth (Biston betularia), in heavily polluted areas is an extremely famous example of supposed evolution in action (a.k.a. 'survival of the fittest') and consequently has drawn a very great deal of study and heated debate. From everything and anything convincing I've ever read however, the basic conclusion I've drawn is: it's a fact! You'll find no better, more balanced account than Michael Majerus' book above.
Finally, I can't help but end with a comment on the truly wonderful 'folk law' names of moths. The Oak Beauty, The Burnished Brass, The Twin Spot Quaker, Mother Shipton...- the list goes on an on. I commend the following link to one of my all time favourite poems: All These I have Learnt, by Robert Byron.
Sunday, March 8, 2009
Photo 1 shows a photo of what is, I think, my favourite garden bird, the Song Thrush (Turdus philomelus), snapped on a snowy day in February.
In case you're wondering about the piece of wood lined with seeds in the foreground incidentally, I can tell you it is the latest in the small arsenal of apparatus I'm acquiring to catalogue my garden's natural history. Ladies and gentlemen I present to you...(drum roll)...The Walloon IR-Beam-Breaker!
Photo 2 explains: Having often been frustrated at seeing a bird on my lawn that I've been too slow or too far away to photograph well, and having a modicum of electronics knowledge, I've recently cobbled together a system for automatically capturing photos. With the cable in photo 2 plugged into my camera, anything crossing the line between the two margarine tubs interrupts an invisible, (harmless) infrared beam and sets off the camera's shutter. Though its rightful place might be my dedicated robin posting, you can see a robin in photo 3 kindly demonstrating the correct technique.
Anyway, back to the star of today's posting. What I've leaned about the Song Thrush (Turdus philomelus), has mostly come from the pages of Eric Simms British Thrushes (New Naturalist Series).
Thrushes are a large, globally distributed genus that includes the blackbird, the American Robin and the Ring Ouzel (an occasional visitor to the UK and perhaps the bird I'd most like to see incidentally).
Song Thrushes average about 32cm long and 74gm. The feathers on their back are a warm brown and they have a creamy-white, speckled breast. (The superficially similar Mistle Thrush (Turdus viscivorus) is about 4cm longer and has a whiter breast). Song Thrushes have a characteristic direct flight, easier seen than described (Mr Simms quotes speeds of around 48kph).
Song Thrushes breed from early March through to July and moult in July. UK birds typically do not migrate any great distance, though birds that do, do so around October.
Song Thrushes have a lovely piping voice (you can hear a clip on the RSPB site). Their repertoire can include imitations of other birds and supposedly even car alarms and the trilling of mobile phones. Singing peaks around April/May, when birds are most active in breeding and defending territories. One physiological trigger for singing is temperature: Mr Simms describes his own careful observations on how singing in his garden thrushes correlated with ambient temperature and also mentions that some researchers have induced premature singing in thrushes in winter by artificially raising the temperature.
In a study of territorial behaviour in Oxford, male/female pairs of Song Thrushes were observed to hold territories of around 150feet square during the breeding season. During winter, most territories were held by solitary males, though occasionally one would be held by a solitary females. (No doubt there's enough ecological complexity underlying this behaviour to motivate a whole PhD's-worth of research, if indeed such a study hasn't already been done).
It's not uncommon on a country walk here in the UK (does this happen elsewhere?) to hear the 'tap tap' of a Song Thrush engaged in the business of removing the shell of a snail by smashing it against a rock ('a thrush's anvil'). You can find some video footage on the RSPB site. Interestingly, Mr Simms says that snails tend to be a last resort food for Thrushes - their preference being worms, insects and berries (including those of Holly, Ivy, Yew, Honeysuckle and Hawthorn). Something I had not hitherto known was that Song Thrushes will forage on shorelines where they've been recorded feeding on periwinkles, dogwhelks and sandhoppers.
I'll close with a personal comment: For me much of the fascination and enjoyment of natural history comes from trying to acquire a smattering of 'scientific' understanding about my garden's life. At the same time of course, like everyone, I have an emotional response to the things I see. Actually however, in the case of garden birds, although I find them wonderfully formed and love to hear their singing, I personally don't find them 'cute' or 'charming' in the way I think some people do. I've heard the idea that birds evolved from dinosaurs ("dinosaurs that grew feathers"). The scientific truth of this is hotly disputed and I don't know enough of the debate to knowledgeably comment, but watching blackbirds scurrying around on my lawn, for me there is more than a passing resemblance to a hunting pack of miniature Velociraptors! No one's said it better than English poet Ted Hughes in his poem Thrushes
Terrifying are the attent sleek thrushes on the lawn,
More coiled steel than living - a poised
Dark deadly eye, those delicate legs
Triggered to stirrings beyond sense - with a start, a bounce,
Overtake the instant and drag out some writhing thing.
No indolent procrastinations and no yawning states,
No sighs or head-scratchings. Nothing but bounce and stab
And a ravening second.