Common darters in Broadview

After going into college for extra meetings today, I got out into the College's Broadview Gardens to look for insects and in particular for dragonflies around the ponds.

There were reasonable numbers of Common Darters, Sympetrum striolatum, generally, at least a dozen in Broadview Gardens as a whole, but particularly concentrated today on the large wildlife pond on the Western margin of the gardens. At one time I was able to count three ovipositing pairs and four other males all in the "hotspot" of a couple of square metres of water weed and marginal vegetation in a sheltered bay in full sun. I was able to sneak up through the vegetation to try to get some photographs as they flew low over the water or rested on the marginal plants.

This photo of a pair taken in flight is very blurry, but is here to show how the male in front looks very red indeed. This seems to be to be a darker red than the orangey red that the Common Darter is supposed to show, giving rise to the exciting possibility that these individuals are Ruddy Darters, Sympetrum sanguineum, rather than just Common Darters.

However this close up below, of another individual caught resting, perhaps after mating, shows a yellow stripe on the foreleg tibiae fairly clearly. Yellow striping on any of the legs is one of the diagnostic features of all the darter species found in the UK, except the Ruddy Darter that I am trying to find. As I can see these stripes on at least some of the photos of some of the redder individuals that I have seen today, regretfully I have to admit I can't claim to have seen any Ruddy Darters today, they must all be assumed to be Common Darters!

Another diagnostic feature is the pattern of black markings on the forehead or frons of the darters. In the Ruddy Darter, this should extend down the front of the face just in front of each eye in a sort of moustache pattern. As you can see from the picture below, as well as the one above, the black marking doesn't actually extend downwards in front of each eye, which is further confirmation that these insects are in fact just Common Darters.

Another feature of the Common Darter, as opposed to the Ruddy, are the clear yellow diagonal stripes on the side of the thorax, which I think are better seen in the picture below. I think you can see the front one fairly clearly, and just the start of the second one behind it;

And then there is the shape of the abdomen from overhead. In the Ruddy Darter there should be a distinct waist, centred around segment 4. Although there is some suggestion of this in the first of the two photos below, in the end I'd have to come down on the side that there isn't a distinct narrowing, so again the overall conclusion must be Common Darter, not Ruddy.

In the second picture the male claspers are holding a female by the back of the head - this pair are resting just by the side of the pond after a frenetic bout of egg-laying. The claspers appear to be bent at 90 degrees to the horizontal, and this is also suggested in the picture below, taken in flight over the egg-laying area.

The male holds the female by his rear claspers clamped to the back of her head after copulation and they both remained joined and working in partnership while she carries out the egg-laying now that the eggs are fertilised. The male at this stage flies nearly horizontally while the female's body is perhaps horizontal initially but perhaps later when egg-laying is about to start or when flying between indisividual eggs being lad, is inclined downwards by about 45 degrees.

At the point of egg-laying itself, both abdomens are often nearly vertical - it's a bit like a harrier jet landing by changing the angle of its engines and controlling the power output! But in the case of a dragonfly it all happens very quickly indeed, within less than a second, and the pair dip down in unison(?) until the tip of the female's abdomen touches the water surface and an egg is presumably released!

At this point you can often see that the female's abdomen may be wetted by a droplet of water held between the angle created by the tip of the abdomen and the vulvar scale. The shape of the female's vulvar scale itself differs between the different species. Luckily for me the shape in the picture but two above and in this female (below) is consistent with an identification of the Common Darter!

Getting away from the dragonflies, there were a few other bees and other insects about, mainly common carder bees, Bombus pascuorum.

I only saw one hoverfly, an Eristalis species with bright orange panels on the abdomen. Even so I think this may have been another individual of Eristalis tenax, but this time, exceptionally, I think I was looking at the pale form, in contrast to the dark almost black abdomens of the individuals I have generally seen in the area over the last month.

There seemed to be the possibility of a dark face stripe, with dark possibly hairy hind legs, which are the characteristics of Eristalis tenax. However none of these characters were particularly or sufficiently clear, and I certainly wouldn't rely on this identification, there are many other possibilities.

There were even some vertebrates and the autumn birds seem to be coming into play now. The moorhens, Gallinus chloropus, on Sandell Lake were obliging as usual - there were birds on the wildlife pond as well, but far more difficult to get good views of. This is an adult bird, although I only saw the one of the adult pair here today:

Meanwhile there was a juvenile, perhaps the only remaining one here, skulking in the reeds,

To finish off, a domestic cat, perhaps the one belonging to the financial director of the college, was having a good look around in this countryside environment, far away from his or her home territory.

So, overall, a very interesting morning visit, with my uncertainty over whether I'm seeing any Ruddy Darters, fairly convincingly put to bed, although not entirely eliminated, particularly with some of those egg-laying pairs which were very highly coloured!