Monday, October 10, 2011

Two Noctuidae Moths - The Square Spot Rustic and The Setaceous Hebrew Character

I am an amateur naturalist trying to discover everything living in my garden.

Some time ago I blogged (here and here for example) my homebuilt mothtrap. I set the trap out in my garden only a few times during 2009 and 2010. So great was the catch however that I'm still working through a backlog of photos of the species I caught (all critters were released alive after being photographed incidentally).
Two species from August 2009 I'm tolerably confident to have identified correctly (with the help of my copy of the Concise Guide to the Moths of GB and Ireland, by Townsend, Waring and Lewington) are a Square Spot Rustic (Xestia xanthographa) in photo 1 and a Setaceous Hebrew Character (Xestia c-nigrum) in photo 2.

The curious Latin species name 'c-nigrum' makes sense when you know nigrum means 'black in colour', hence literally 'with a black letter ''c''' [on its wings]. (Some of you may remember the 'white letter c' butterfly P. c-album I blogged here.)

I've entirely failed to uncover the meaning of the genus name Xestia. Can anyone comment?

Turning to the English common names of moths, I learnt previously that many were invented in the 1730's by the Aurelain society of naturalists.  I'd guess (but don't know) those of the moths here were amongst them.

I needed to look up setaceous. It means whiskery incidentally.

From the book mentioned above I learn that both my moths are common in the UK. Both overwinter as caterpillars. The caterpillars of the Square Spot Rustic commonly dine on grasses, and those of the Setaceous Hebrew Character on nettles and other herbaceous plants.

My attempt to learn a little more about my moths led me to some interesting papers by Chapman [1] and  Wood [2] and The papers describe the authors' efforts to track the migration of insects using ground-based radar. The papers are full of amazing details: I had not hitherto imagined that ground based radar would be so sensitive as to allow tracking of a single grasshopper in flight at a height of 1.5km. Further, as the authors explain, that around the globe millions of tons of insects are aloft at any instant, or that at least 2.3 billion(!) insects were involved in the migrations to/from the UK between 2002 and 2007.

What it is the insects (many moths, including mine, amongst them) are doing at heights of several hundred metres to a few kilometres is taking advantage of high wind speeds to propel them to places of seasonal migration. The speeds are several times greater than that at which an insect could fly unaided. The authors' studies yielded estimates that by harnessing winds insects may be able to travel as far as ~2000km during only three of four 8-hour flights. Things are not as simple as the insects being mere passive 'leaves in a storm' however. Rather, the authors discovered that they exhibit a clear directional sense, flying at an angle to the main wind direction so as to control where they end up. (I suppose an analogy would be a rowing boat in a strong ocean current. Just because the current may be faster than you could row, by sculling at an angle to the main current it's still possible to steer somewhat). How the insects are able to navigate at altitude and at night the papers don't say. I guess the moon may be involved, but that much about how they do so remains a mystery.

1. Flight orientation behaviors promote optimal migration trajectories in high flying insects, J.W. Chapman, R.L. Nesbit, L.E. Burgin, D.R. Reynolds, A.D. Smith, D. R. Middleton, J.K. Hill, Science 2010, 327, p.682-685

2. Flight periodicity and the vertical distribution of high altitude moth migration over southern Britain C.R. Wood, D.R. Reynolds, P.M. Wells, J.F. Barlow, I.P. Woidwod, J.W. Chapman, Bulletin of Entomological Research 99(05), p.525-535, 2009

Saturday, October 8, 2011

Cat's Ear Hypochaeris radicata

I am an amateur naturalist trying to discover everything living in my garden.

 The pretty flower in photo 1 is Cat’s Ear - a common weed in my garden.  There are a number of superficially similar British yellow-flowered weeds  including  the Hawkbits, Sow thistles and the Hawksbeards I blogged here.  From my copy of The Wild Flower Key (Rose) I’m fairly confident my plant is none of these, though I’m less confident it is definitively Cat’s Ear (Hypochaeris radicata) and not the rather similar Smooth Cat’s Ear (H. glabra). The book tells me that were my plant to be Smooth Cat’s  Ear , then its yellow ‘petals’ would be only twice as long as wide (mine seem longer). Also that the green stems of H.radicata should broaden as they approach the flower head (more correctly ‘the involucre bract’), which appears to be the case for my plant (see photo 2). On this basis I’m going with the identification H.radicata.

Readers of my blog will know I try to do a little research to uncover some point of interest for each lifeform I come across. In the case of Cat's Ear my searches led me to an interesting paper [1] by N. Hartemink The authors asked the question "What does a plant do if you cut the flower buds off?" (these are my words - I'm paraphrasing). A trite answer would be "Grow some more!". Pausing to consider things in more detail however one might begin to imagine more subtle possibilities. Consider a plant growing in a field subject to heavy grazing by animals. If the plant loses a flower one might imagine various responses. For a short lived annual plant, flowering and successfully setting seed in a season is an absolute imperative. One might conjecture that such plants could respond to flower-loss by "stepping up" efforts to produce more and more flowers therefore in the 'hope' that some escape the grazing (of course plants don't 'hope' and this is a poor anthropomorphic description - but, hey, I'm an amateur and it's good enough for me!). By contrast, for long lived perennial plants, flowering does not  have the same urgency. If such a plant has its flowers removed, might it simply 'cut its losses' therefore, put 'on hold' attempts to flower and instead put its energies into growing more leaves and roots?

To add to these considerations, one should remember also that a plant may not have a simple unfettered 'choice' about whether and how many flowers to grow. Resources (food, water and light etc.) are always finite and may impose further constraints on what types of structure (e.g. flowers vs. leaves) the plant is able to produce. A deeper consideration of this resourcing issue has led the experts to formulate such theories as "meristem allocation". (Meristems are specialised regions of a plant where growth 'happens'. Meristem tissue is found at the tips of roots and shoots for example. It is made up of special meristemic cells that are rapidly growing, dividing and transforming into new bits of root, shoot etc.).  I don't understand the 'meristem allocation' theory in detail, but briefly it seems to revolve around the idea that a mersitem at the tip of a plant shoot has a 'choice' to simple carry on creating more and more plant shoot and leaves, or cease making leaves and shoots and instead switch to making a flower. Once the meristem has switched to making a flower however, there is no going back - that meristem is committed and can't later go back to making shoot. In a sense the plant's meristems are like cash in a bank. The plant can keep the 'cash' (mersitems) in the bank growing 'interest' (more shoots and leaves) or 'withdraw' (allocate) some money (meristem) and 'spend it' on a flower. This might all seem rather abstract, but the point is that armed with the idea that meristems are a fundamental unit of 'currency' in the 'economics' of plant survival, botanists can start to construct quantitative and predictive (as opposed to merely descriptive) theories of how plants ought to respond to different environmental pressures (grazing, resource shortages etc.).

So, what does a Cat's Ear do when you cut the flowers off?! Well, the authors above took three plant types: Cat's Ear, Devil's Bit Scabious (Succisa pratensis) and Brown Knapweed (Centaurea jacea). They found marked differences in the reponses of these three to removal of flower buds. Both S. pratensis and C. japea responded to flower bud removal by increasing the number of flower buds. Plants of both species would typically make around 7 flower buds per plant if 'left alone', whilst those plants who had their flower buds removed would 'bounce back' and regrow about 12. Interestingly however, S. pratensis also responded by switching some of its energies away from flower bud growth into increasing growth of plant side 'shoots' (strictly side 'rosettes' of new leaves). Appropriately for this blog posting, Cat's Ear's response was the most dramatic all. Plants 'left alone' produced around 60 buds. The 'decapitated' however, bounced back with a dramatic 240. There is much more in the paper that I could talk about, but I've gone on enough here and will simply refer you to the original if you're interested. What I like about the work is it is true science and yet an experiment that any motivated amateur could repeat and extend: find a patch of weeds and a pair of secateurs and you're all set to become a published scientist.

[1]  Flexible life history responses to flower and rosette bud removal in three perennial herb, Nienke Hartemink, Eelke Jongejans, Hans De Kroon , Oikos 105: 159-167, 2004.

Sunday, June 19, 2011

Scenedesmus algae

I am an amateur naturalist trying to discover everything living in my garden.

Some time ago I wrote about a puddle I spotted in my garden. Of course, I bought it into my house in a fishtank (doesn't everyone do this with their garden puddles?!).  It was only last week, nine months on, that I finally returned it to the great outdoors. Amazingly it was still brimming with microscopic 'pondlife', although it had become rather choked with the 'sludgy' cyanobacteria I wrote about here.

Over the months I repeatedly examined my puddle under the microscope. Photo 1 shows one of the lifeforms I found.  This one was rather common in the early days, but later seemed to disappear.

Spot something tiny and green under the microscope and its either algae or cyanobacteria. Cyanobacteria tend to be featureless, lacking detailed internal structure, notably a nucleus. The cells here have nuclei however, helping to identify them as algae. (The nuclei don't show up very clearly in photo 1 but by squinting I think you'll be able to see the spherical features towards the centres of the upper three cells).

Turning to my (borrowed) copy of the hefty "The Freshwater Algal Flora of the British Isles" (John, Whitton, Brook) - a 700-page light bedtime read! -  I was able to identify my algae as a member of the Scenedesmus genus. Characteristic features are the obviously 'pointy' crescent shape. Also, although I occasionally found single, isolated cells, very often I found 4 (as here) or 8 cells together (about which more shortly...).

Scenedesmus algae are part of the Chlorophyta (= the green algae). They are all freshwater. According to the book above as many as 200 different British species have been reported. However, it's been found that individuals from a species can grow into a variety of different forms as a result of different environmental stresses, so there's suspicion that many of these 200 'species' may not be unique. Furthermore the authors explain that recent scientific studies powered by advances in electron microscopy and modern-day biochemistry are pointing to a need to significantly rethink the traditional classification of many species. (This is happening everywhere in biology these days - see my posting on mushrooms here for example). All this means that although the authors give a key to the 42 British species of Scenedesmus algae they recognise, I've not attempted to pin down the species-identity of mine.

As I've said many times, I'm rarely disappointed when it comes discovering that there is some fascinating or unusual feature in the lifestyle of any creature I come across. Turning to my copy of R.E.Lee's Phycology (a present Christmas-last) it turns out that the fact I frequently saw 4 or 8 algal cells together was no accident.  If Scenedesmus is grown in a tank free from predators (such as grazing water fleas) it grows as single isolated 'unicells'. (If you're an algal cell wanting to maximise the amount of sunlight and nutrients reaching you its preferable to keep your distance from neighbours who might otherwise shield or shadow you). However, introduce some predators into the tank and, amazingly, Scenedesmus cells switch to growing in small groups as an anti-grazing defence! In the jargon, a group is known as a coenobium. Some groups also grow long spines, although interestingly the book implies that these are flotation devices to help the colony stay in the light, rather than anti-predator devices per se. The algae are able to detect the presence of predators by detecting chemicals ('infochemicals') in the water that leach from the digestive tract of the predators. Another of nature's tiny miracles!

Friday, June 10, 2011

A Mock Orange Tree - Philadelphus coronarius

I am an amateur naturalist trying to learn something about everything living in my garden.

Photos 1 and 2, taken a few days ago, shows the Mock Orange (Philadelphus) bush that grows at the back of my garden. It is a large plant (maybe 4m x 4m) and a fabulous site in early summer.

And yes, it smells as gorgeous as it looks! A rich honey/jasmine aroma that wafts across my lawn on summer evenings.

Philadelpus has long been popular with gardeners and plant nurseries stock numerous artificial cultivars. The Mock Orange (genus Philadelphus) and 'true' Orange (genus Citus) are really only distantly related. The genus Philadelphus is part of the large Hydrangeaceae family of plants.  I found a species-key here, and my plant keys out as Philadelphus coronarius.

Seeing a thin dusting of yellow pollen on many of the leaves I was inspired to get out my trusty student microscope. I enjoy fiddling around with microscopes and I'm a little surprised that in many years of doing so I've never before looked at pollen. For any beginnner like me who wants to have a go, there are a few tips it may help to know:

Firstly, something I hadn't previously realised is that plants release their pollen in a dehydrated state (15-35% water content is typical [ref.1]). I guess (but don't know) they do this to keep their weight low and so assist their transportation by wind or insects. Also, desiccation may help prolong the active lifespan of the grain. Dehydrated and hydrated grains can look significantly different (see photo 3).

A second thing it helps to know is that pollen grains often have a waxy surface coating. This can be a nuisance for microscopy as it may cause grains to stick together. It also obscures fine surface features of the grains.

Fortunately, both rehydration of pollen grains and removal of their waxy layer is easily achieved by simply wetting them with a few drops of alcohol.

Once you've looked at your pollen slide you can of course simply throw it away. Microscope users will know however, it is possible to make a collection of semi-permanent slides by encapsulating specimens in glycerine jelly. You can buy glycerine jelly especially designed for pollen. The jelly contains red dye that stains the grains and makes it easier to see fine details on their surfaces.

Anyway, photo 3 shows the results of the above: circular/triangular pollen grains about 12microns across.

Seeking to learn some more about pollen, I came across a nice review paper by Edlund here [ref.1]. The paper highlights various areas where the science behind pollen is unexplored or only partly understood. Take for example the functioning of the outer coating of pollen grains (the exine). This layer can be extremely ornate. Often it is riddled with cavities containing exotic plant proteins. When a dehydrated pollen grain lands on the 'female' stimga in the centre of a flower of the same species, something about the surface of the grain causes it stick fast, when pollen from a different species doesn't. The science behind this 'selective adhesion' is only partly understood.

Once a grain has stuck, chemicals are exuded by the stimga that rehydrate the pollen in a matter of minutes. Once again, this can be exquisitely selective. Two species of pollen grain can be put, side-by-side, onto a single stigma, and only the pollen grain from the correct species will be rehydrated. How nature manages to pull off this clever stunt is again something of a mystery.

With the grain re-hydrated, it germinates and sprouts a single tube that grows its way down the stimga. (There's a fun article by Chris Thomas here that describes how to observe pollen tubes by sprouting grains on a piece of onion skin).  Eventually the pollen tube contacts with a female egg at the base of the stigma and the pollen grain sends its DNA down the tube to fertilise the egg. (Pollen grains are a mechanism by which DNA is carried between plants. Its wrong to think of them as 'male sperm' however since a pollen grain is mostly comprised of bundles of 'normal' vegetative plant cells.)

Some plants rely on wind to spread their pollen. Others, animals and insects. Something new I learnt was that one plant- Lagerstroemia - is so keen to attract the latter it produces two types of pollen: a sterile, yellow, feeding pollen and a fertile, blue one.

My first microscope observations of pollen were great fun and I learned a lot. It turned out my Mock Orange had an another interesting microscopic feature for me. What it was however, will need to wait for another posting.

[1] Pollen and Stimga Structure and Function, A.F. Edlund, R. D. Swanson, Preuss, The Plant Cell 16:S84-S97 (2004)

Saturday, June 4, 2011

Hedge Bindweed Calystegia sepium

I am an amateur naturalist trying to discover everything living in my garden.

Photos 1 and 2 show some Hedge Bindweed (Calystegia sepium) - a weed that pops up frequently in my garden.

My copy of The Englishman's Flora (Geoffrey Grigson) lists dozens of alternative names for this common plant, from the pretty Rutland Beauty, Shimmy-and-Buttons and Robin-run-the-Hedge,to the sinister  Devils Garter, Strangleweed and Devil's Guts.

A name not in the book is the one my mother taught  - Granny Pop the Bed - so called because if you squeeze the green base of the trumpet shaped head (see photo 2) the white flower pops out. It's not a very convincing pop it has to be said, but hey, when you're six its great!

In the jargon, the green flower base is called the calyx (I've labelled this in photo 2). The 'leaves' that make it up are called sepals. C.sepium also has an outer epicalyx.

When I first started this posting I took it for granted  that a web search would turn up scores of scientific papers on my common weed. As it turned out I struggled to find any! I did come across a research paper [1] on the apparently unusual lectin (a protein) biochemistry chemistry of my weed, but the subject matter was rather technical and I'm not expert enough to do it justice here. This aside most of the material I did manage to find concerned the related Field Bindweed (Convolvulus arvensis), a target for frequent study because it is a major weed of arable crops. (Field- and Hedge Bindweed can be readily distinguished by  knowing that Field Bindweed doesn't have an epicalyx).

This lack of literature meant that for a time I was left wondering what to say in this post, but then I recalled an unusual fact concerning Bindweed's spiral growth which I'd read about some time ago (I don't remember where). Photo 1 shows a plant climbing a garden cane. As it climbs the stalk is seen to spiral in an anticlockwise direction (as viewed from above). What's interesting is that C.sepium always spirals anticlockwise. (I've even been around my garden checked! Indeed once you know this fact, its hard resist the temptation to check the spiral of every Hedge Bindweed you see anywhere!).

This feature of always twisting one way  turned out to be rather a rich topic for exploration. Amongst others I was led to a paper by Thitamdee [2] on the origins of spiral forms in plants:

The authors' studies focused on plant microtubules.  These are molecular sized rods found in both plant and animal cells (they've received mention on my blog before, here). Its been discovered that large numbers of these rods decorate the surface of plant cells (like matchsticks stuck on a balloon). The rods do not lie randomly on the surface of the cells however, rather they order themselves so as to line up along a common direction. There's some amazing video of real microtubules jostling about on cell surfaces on the webpage of Indiana University's Shaw Lab. here.  Now, to continue the balloon analogy, imagine having a lot of matchsticks densely glued to the surface of one of those sausage shaped party balloons. Imagine the matches are all lined up so as point around the short, circular axis of the balloon (like hoops around a barrel). Next, imagine blowing more air into the balloon. Though I haven't actually done the experiment, I hope its reasonable to suggest that the rigid matches would make it more difficult for the balloon to swell  in circular cross-section (get 'fatter'), and instead the balloon would grow more freely lengthwise (get longer). This is exactly what aligned microtubules are believed to do for plant cells  i.e. cells that would otherwise grow and expand as simple spheres are instead constrained to grow and expand along a preferred direction. This is useful because it allows the plant to create e.g. long, thin cells suitable the plant stalk. (Actually, strictly its not microtubles themselves that constrain the growth of the cell walls,  rather the microtubles appear to act as markers for the laying down of a secondary stiffening material - cellulose - but the principle's the same)

Now, Thitamdee were studying a cress plant called Arabidopsiss. This is famous amongst botanists as the plant for genetic studies worldwide. Normal Arabidposis plants don't spiral,  they grow straight. Furthermore, when scientists looked at the microtubules on cells in the stalk they found them to be arranged exactly as in the description above (i.e. 'hoops around a barrel')

What Thitamdee discovered however, was that a mutation in a single gene can cause a change in the way microtubles on cells in the stalk of an Arabidopsis plant arrange themselves. Specifically, they observed mutations that caused the microtubules to shift from being aligned all-parallel to the cell circumference ('hoops around a barrel') to instead all lying on the cell surface at an angle to the long axis of the cell.

And what did these mutant plants, with their slanted microtubles, do? Yep, grow in a spiral!

The importance of this work is that it implies an explanation for why some plants spiral and some don't, and furthermore why, for many species, every individual must spiral in the same direction: Things are dictated by the angle at which microtubles are aligned on the cells. This in turn is hardwired by the plant's DNA.  Perhaps an ancient ancestor of Hedge Bindweed grew straight. At some point however a gene mutation arose that caused the microtubles to align at some new angle. With this angle fixed by the DNA, the Bindweed's fate was fixed; Subservient to the constraining forces acting on its cell walls, it was doomed to spiral, and always in the same direction, this being dictated by the angle of microtubule alignment (though what this is specifically I don't know -  I haven't found any reference to suggest the microtuble alignment of C. sepium specifically has been studied).

To end, a bit of humble pie. When I first recognised the anticlockwise spiralling of Bindweed, I admit I thought I was rather clever in having uncovered some little known fact... until, that was, I discovered that my supposed 'little known fact' even had its own popular 1950's song!

The fragrant honeysuckle spirals clockwise to the sun, 
And many other creepers do the same.
But some climb anti-clockwise, the bindweed does, for one,
Or Convolvulus, to give her proper name... 

( from Misalliance by Flanders and Swann, ).

The Crystal Structure of the Calystegia sepium Agglutinin Reveals a 
Novel Quaternary Arrangement of Lectin Subunits with a Prism Fold,  Y Bourne, The Journal Of Biological Chemistry, 279(1),pp. 527–533, 2004
[2] Microtubule basis for left-handed helical growth in Arabidopsis, S. Thitamadee, K. Tuchihara & T. Hashimoto, Nature, 417, p.193, 2002.

Thursday, June 2, 2011

A Grey Squirrel Sciurus carolinensis

I am an amateur naturalist trying to learn something about everything living in my garden.

Photo 1 (strictly I took this particular photo in a local park) shows a sporadic visitor to my garden, and my third mammal, the Grey Squirrel (Sciurus carolinensis).

To learn something about them I have been reading Squirrels by Jessica Holm (Whittet Books).

Together with the Red (Sciurus vulgaris) the Grey is one of two species of squirrel found in Britain. It is a North American import. The first pair was released by a Mr Broklehurst in the county of Cheshire in 1876. Famously, the Grey has thrived (indeed, they are legally classified as vermin), whilst the once common Red is today a protected species clinging on in a handful of isolated locations (I have only ever seen one myself- in Cumbria).

Why the populations have changed in this way is not entirely understood. It is often said (indeed, before reading Dr. Holt's book I too had lazily assumed) that the Greys have 'driven' the Reds from their 'territories'. This is false on two counts however: Firstly, in woodlands where both have been studied together its found that Reds and Greys do not show any undue aggression towards one another. Secondly (and a surprise to me) squirrels aren't territorial animals. The life of a squirrel is a 'roaming' one (though generally confined to some home range of a kilometer or so). Rather than all-out interspecies hostility, it seems that the Red population may have declined as a combination of diseases passed on by the invaders and because the smaller size of the Reds means they are less able to gather food in areas where the more avaricious Greys are eating much of it up. Totally, more study is necessary however.

A few additional things of interest I picked up from my reading are firstly that Reds and Greys normally carry distinct species of flea (Monopsyllus sciuronum for the Reds, Orchopeas howardii for the Grey). Mother Nature is nothing if not an expert in specialisation! Secondly, watching a squirrel work through a pile of nuts, it will sometimes be observed to discard one without opening it. These turn out to be bad nuts with withered kernels. How the squirrel determines this with the nut still in its shell is rather impressive. It weighs them in its paws. A neat party trick!

To end, the literature abounds with Squirrel poems and Beatrix Potter quotes, but for me there is only one winner of the prize for top squirrel literary moment:

The squirrels pulled Veruca to the ground and started carrying her across the floor.
"My goodness she is a bad nut after all" said Mr Wonka, "Her head must have sounded quite hollow" [...]
"Where are they taking her?" shrieked Mrs Salt.
"She's going where all the other bad nuts go" said Mr Willy Wonka. "Down the rubbish chute."
[Roald Dahl, Charlie and the Chocolate Factory]

Tuesday, May 31, 2011

A long legged Dolichopus fly

I am an amateur naturalist trying to discover everything living in my garden.

For some time I have hankered after a garden pond (there are few things better for encouraging wildlife into one's garden). On a whim, I recently took the plunge (sorry, terrible pun!) and dug one. Though only a few weeks old, already I'm seeing enough life to keep me busy blogging long into the future.

Photo 1 shows two flies sunning themselves at the water's edge. There were several dozen around the pond.
The 'colony' was a constant flicker of activity and it was this that first caught my attention. Individual flies seemed to be attracted to movement and if another landed closeby they would quickly go 'into action', advancing rapidly towards the new comer. In a few cases one would even jump on top of another and the two launch into flight (at which point it was impossible to follow them by eye).

I observed a number of instances of one fly standing close by another and methodically rubbing its back legs together.  I've highlighted this with an arrow in photo 2. I recently wrote at length about  the courtship signalling behaviour of a related fly (Poecilobotus nobilatus) I found in my garden. I would like to think I was observing something similar here. Whether I was however, or whether it was just some coincidental preening I can't be sure (can anyone comment?).

So, how about the identity of my fly? Unfortunately, for the non-expert (=me!), identifying a fly is a decidedly non-trivial business. Firstly, a low power microscope is pretty much essential. Next, you need to be fortunate in finding an identification key. After that you need to be prepared to work through the copious technical jargon that the specialist keys will hurl at you. Finally you need the magic ingredient: experience!

How did I fair against this list? Well, I have a microscope; I was also fortunate to find the free online key by Dennis Unwin to the families of British Diptera, and "A Key To Swedish Dolichopodidae" by Igor Grichanov; For several hours I diligently applied myself to translating the jargon in the keys and scrutinising my fly's features. I was able to determine that my fly's "post ocular setae" (=bristles behind the eyes) are long and all of them black (see '1' in photo 3). Also, that the base of my fly's antennae sprout tiny hairs (see '2' in photo 4); that the shape of it's  "occiput" (= the back of the head) is convex (see '3') and that it sprouts two rows of "acrostichal setae" (=hairs down the centre of its back - see '4'). I worked through a dozen other similar features.

And the result of all my efforts? Well, further aided by a study of my fly's wings (see my discussion of insect wings here) I'm confident that amongst the 80-odd families of British fly, mine is a member of the family Dolicopodidae. Next, I'm fairly confident that of the 30-odd genera within this family, mine is a member of the Dolichopus genus. And finally, of the 51 British species within this genus (I got this number from the Dipterists Forum website)... well, I am not at all confident (!) mine is a Dolichopus ungulatus.

The one thing you can't look up is experience.