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Featherleg Differences

11/1/2016

2 Comments

 
by Bruce Hyde​

Dragonflies (the order Odonata) have two suborders - dragonfly (anisoptera meaning unequal wings) and damselfly (zygoptera meaning equal wings).
  • dragonflies (anisoptera) are larger and very much more obvious when you see them flying around.
  • damselflies (zygoptera) are normally quite small, and if you are not looking out for them you can easily walk right by without seeing them at all.

Having talked in an earlier blog about differences in one dragonfly species, Pincertails, I am going to cover a genus of damselfly which has 3 species in France: the Featherleg.
 
Damselflies are dainty insects. Featherlegs measure about 30 - 35 millimetres long overall, and their abdomen is only just over 1 mm thick. So certain parts of the body from which positive identifications can sometimes be made are very small - indeed some of the details on the pronotum (see further on) measure about one tenth of a millimetre across. In itself this presents useful photographic challenges (particularly as in getting my photos I never disturb the insect any more than possible, and never catch them).
 
The Featherleg (Platycnemis) forms in France are
  • White (P.latipes/L'Agrion blanchâtre)
  • Blue (P.pennipes/L'Agrion à larges pattes)
  • Orange (P. acutipennis/L'Agrion orangé)
 
Until recently I had thought that all three species were resident in our area, and I was having a lot of difficulty in determining which was which in my photo library, especially some of the females. I then looked more closely at a map in "Les Libellules de France, Belgique et Luxembourg" by Daniel Grand and Jean-Pierre Boudot - and life became easier. For some reason (unknown), in this South Eastern corner of France, the Blue featherleg is absent from Pyrénées-Orientales and rare in Aude. Thus the Orange and White forms are almost certainly the only ones I have been seeing. (At the same time one has to be aware that there just might be individual vagrants of the Blue form flying in from neighbouring areas).
 
So here are the 2 species this blog is about - 



Typical Males
Picture
White Featherleg male (Platycnemis latipes)
Picture
Orange Featherleg male (Platycnemis acutipennis)
​Superficially there is not a lot of difference between the males, except for the colour of the abdomen. However the females are very alike and, as always, the devil is in the detail!
 
Before going any further, lets look at some of the basic parts of a damselfly's anatomy.
Picture
Orange Featherleg female (Platycnemis acutipennis)


The Latin word Platycnemis comes from the Greek "platos" meaning flat and "cnernis" meaning shin. The tibia of the hind leg is wide and flat, more so in the case of the White Featherleg than the Orange, and all the legs have hairy bristles giving a somewhat feathery appearance.


Flat tibia with hairy edges
Picture
White Featherleg male (Platycnemis latipes)
​There are a number of details of the insect's body from which one can make a positive identification. Thorax, abdomen and legs are all useful, although more so collectively than individually. In the case of females, the pronotum at the front of the thorax will give a positive ID, but it needs a very clear view, in good focus, as it is so very tiny (more about this later).
 
Featherlegs often have a double stripe running along the side of the thorax - the antehumeral stripe. While this feature is diagnostic of a featherleg, it is not always present. 
Picture
White Featherleg male (Platycnemis latipes)
​Males can quickly be distinguished from females by the appendages at the end of the abdomen. Male appendages are claw shaped to grasp the female when they are mating. Female appendages are contained in the swollen end of the abdomen.
Picture
White Featherleg male appendages
Picture
White Featherleg female appendages
​When mating they often form into a heart shape, which is quite charming -
Picture
White Featherlegs mating (Platycnemis latipes)
Males of the two species are separated by their colour when they are mature; females tend to be similarly coloured and are distinguished by features of their pronotum (see below) and to some extent by leg markings.
 
Male Featherlegs
The typical male White featherleg has a white abdomen, often looking porcelain-like or translucent, whereas its Orange counterpart has an orange body. They both have blue eyes and there are black markings on the last few segments of the abdomen, although the extent of these is variable.
Picture
White Featherleg male (Platycnemis latipes)
Picture
Orange Featherleg male (Platycnemis acutipennis)
​Looking more closely at the legs it can be seen that the White has got broader, flatter tibias than the Orange. 
Picture
White Featherleg male, broader, flatter tibias.
Picture
Orange Featherleg male, tibias less broad
​Male Whites have a stripe running down the middle tibia which extends about one third of the way; this stripe is usually absent from the hind tibia. The Orange has a stripe on the middle tibia which goes all the way down, and one on the hind tibia that goes about half way down. These features are diagnostic of the male (females are different).
Picture
White Featherleg male, middle tibia stripe
Picture
Orange Featherleg male, middle and hind tibia stripes
​The eyes of all featherleg species, both male and female, are widely spaced. In the case of males they are an attractive blue colour.
Picture
White Featherleg male eyes (Platycnemis latipes)
Picture
Orange Featherleg male eyes (Platycnemis acutipennis)
Female Featherlegs
The females are harder to tell apart. Although the typical Orange female often has a darker coloured abdomen, this is not always so as the colour probably darkens as the insect get older. Immature females of both species are very similar.

Typical Females
Picture
White Featherleg female (Platycnemis latipes)
Picture
Orange Featherleg female (Platycnemis acutipennis)
​The tibias of the female White are not as broad as the male, and in the case of the Orange they are not broadened at all. Unlike the males, the stripes on the tibias cannot reliably be used for identification, although in the Orange the stripes usually go at least half way down the tibia on all legs.
 
The eyes of both featherlegs are variable, some having blue patches and others being brownish for instance; the colours can look as though they are in layers. Here are a couple of examples.
Picture
White Featherleg female (Platycnemis latipes)
Picture
Orange Featherleg female (Platycnemis acutipennis)
​Pronotum
The most certain way of separating a female White featherleg from an Orange is by carefully examining the pronotum. This is not easy and one has either to be very close indeed or have a detailed photo.
 
This picture shows the pronotum of a female White featherleg. It is shaped like an inverted "V" on top of the thorax where the front legs join. In this case the colour is light brown, but it can vary and is sometimes black.
Picture
White Featherleg female (Platycnemis latipes) pronotum
​The White featherleg's pronotum has a clear lump on the top, is a bit knobbly and has very small bumps on each side at the lower end.
 
Compare this with the pronotum of an Orange featherleg where, instead of small bumps, there are large spikes (technically "sublateral spines"). This feature may not be very obvious as the distance across the body from spike to spike is only about 1mm; this added to the relative shyness of Orange featherlegs makes the getting of detailed pictures quite difficult.
Picture
Orange Featherleg female (Platycnemis acutipennis) pronotum spike
​A slight aid to identification is the flight season. White featherlegs fly from mid-June until late September with the main months being July and August. Orange featherlegs fly from late May until mid-August, with the main months being June and July. These periods are not fixed and can be a week or two longer at either end.
 
Featherlegs like slowly running water such as some reaches of the River Tech, although I have seen them on canals.
 
They are often approachable, especially the Whites which almost seem to enjoy being on camera! 
Picture
Damselfly habitat on the River Tech
​Males like to perch on low vegetation near a river bank, and search for prey and mates with a slow zig-zagging or bouncing flight. Their wide tibias are not used in courtship, but as threatening behaviour to other males of the same species in flight.
 
Both the featherleg types in this blog are found in southern France, the Orange occupying south of a line from roughly the Cherbourg peninsula to Monaco, and the White south of a line from Bordeaux to Monaco.
 
In this blog I am referring only to featherlegs I have photographed on the banks of the river Tech near Montesquieu-des-Albères. In other areas of France they may have slightly different characteristics and may be easier (or harder) to identify.
 
There is little better than sitting in the shade on a river bank on a sunny day watching the fascinating behaviour of these tiny insects. 
2 Comments

Dragonfly Differences

10/3/2015

1 Comment

 
Large vs Small Pincertails (Onychogomphus uncatus vs. forcipatus)

My first interest in dragonflies came from their often vivid colours, and the sheer difficulty of photographing them in their swiftly-moving, jerking flight patterns. They are one of the very few animals that can fly up, down, backwards, forwards and sideways.

I have become fascinated by the sheer difficulty of distinguishing one species of dragonfly from another. Despite helpful pictures in many books, it can often be hard to make a good and accurate ID.

In an earlier blog "Oh! So Similar" I talked about the way that many dragonflies at first seem to look so alike. Now I am going to look at two species of dragonfly that are very like each other and show what I feel are good ways of telling them apart. The species is Pincertails (Onychogomphus in Latin).

This commentary covers only Pincertails found in the Mediterranean area of S. France that lies at the foot of Les Albères in the Pyrenees, near the river Tech.

There are two species of Pincertail (Onychogomphus) in this area - Large and Small Pincertails. They are called Pincertails because of the eye-wateringly substantial male appendages; these are used during copulation by the male to grasp the female. Telling the difference between Large and Small can be tricky as the overall sizes of the two are not all that different.

Picture
Large Pincertail male (Onychogomphus uncatus)
Picture
Small Pincertail male (Onychogomphus forcipatus)
Picture
The male "Pincer Tail" - Small Pincertail (Onychogomphus forcipatus)
I have found the Large Pincertail to be the less common of the two, having only seen 2 examples. It appears they are less plentiful in the lower reaches of rivers, existing at heights of up to 800 metres, and as a species is rarer than the Small Pincertail.

The Small Pincertail has three subspecies, of which only one is found in this area  (Onychogomphus forcipatus ssp. unguiculatus). All O. forcipatus pictures in this blog are of the subspecies.

In telling the difference between Large and Small there are three (fairly) visible markings which are usually straightforward to identify and are diagnostic.

Starting at the front with the first of these diagnostic markings -

In the Small Pincertail (O. forcipatus) the vertex - the black area between the eyes - has got a small yellow mark.

Picture
Small Pincertail (O. forcipatus) yellow vertex mark
The Large Pincertail (O. uncatus) has an all-black vertex.
Picture
Moving back a little for the second diagnostic marking -

Both species have a yellow collar at the front of the thorax (not always easy to see). In the Large Pincertail this is broken by a black bar. 

Picture
Large Pincertail (O. uncatus) Yellow collar broken by black line
The Small Pincertail lacks this black break.
Picture
Small Pincertail (O. forcipatus) No break in collar
Finally the third diagnostic marking -

In the back wing, both species have got a triangular area close to the body at the rear of the wing called the anal triangle.

In the case of the Large Pincertail male this triangle contains four cells...
Picture
Large Pincertail (O. uncatus) Four cells in anal triangle
....whereas the Small Pincertail male's anal triangle contains only three cells
Picture
Small Pincertail (O.forcipatus) Three cells in anal triangle
There are other markings that can be used or ID, but in the pincertails I have seen these are either quite variable and therefore not really diagnostic (see below) or require the dragonfly to be caught for detailed observation (for instance tiny differences in the tail pincers).

In the case of the Small Pincertail below there are two curving black lines running front to back on each side of the top of the thorax; these should be joined about half way along by another curving black line. On one side the line clearly joins but on the other not very clearly.

Picture
Small Pincertail (O. forcipatus) Do the lines join?
A comment on nomenclature.
In the case of many dragonflies there tend to be different English names for each species. These vernacular names need to be as user-friendly as possible. The names proposed in a classic reference work by Klass-Douwe Dijkstra (K-DD) - "Field Guide to the Dragonflies of Britain and Europe"- are becoming widely preferred, mainly because they are more descriptive. The British Dragonfly Society (BDS) names can have a more regional focus.

For example the Small Pincertail (K-DD) is also called Green-eyed Hooktail (BDS); in our area these have blue eyes (a Mediterranean trait, see photo above), and the name Hooktail is less descriptive than Pincertail.

Elsewhere in the world (e.g. USA) names can yet again be different. There is a need to standardise international names for European species, and currently we are seeing polarisation rather than consensus.

The definitive name is always the Latin one. Even so, this is not always clear as there is discussion on which species a dragonfly belongs to (especially in the case of sub-species - is it a variant of an existing species, or an evolving/evolved new species).

Dijkstra                        BDS                           French                               Latin

Pincertails                    Hooktails                     Gomphidé                           Onychogomphus    
Large Pincertail             Blue-eyed Hooktail       Le Gomphe à Crochets        Onychogomphus uncatus
Small Pincertail             Green-eyed Hooktail     Le Gomphe à Pinces           Onychogomphus forcipatus


Challenging photography....
It is quite clear that making a good ID requires detailed observation. Many of the details are not possible to see without first catching the insect, either because what you want to see is very small or just hidden away from view. I never catch dragonflies; my wish is to leave them as undisturbed as possible. This means that I rely on photographs.

The trick is knowing which anatomical parts of which species require  detailed photos - and then getting into a position where one can get the shot. Even the most approachable of insects will tolerate only a limited amount of photographic time, and there are many which are either very shy or on the wing most of the time. Bearing in mind that the feature one is trying to photo may be only a fraction of a millimetre in size, awkward to view and obscured by foliage, and one can understand how challenging it is!

To come....
The next blog in this series will be looking in detail at a small and dainty damselfly - the Featherleg (Platycnemis). There are three species of Featherleg in our area, but two of them are really difficult to sort out - especially the females.

A further blog will look at the habitats these delightful creatures live in, how difficult it can be to get the "right" photos and ways to tackle the problem.

1 Comment

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    Isobel Mackintosh
    Lesley McLaren
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