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A work in progress
This reflects my approach to ID. Others may think there's a better way or that it should be presented in a different order - that's fine you can do it that way on your website! This page covers the three darter species encountered regularly in Hampshire plus Red-veined Darter a few of which which are seen most years.
I have tried to use photos which well illustrate the ID features. In the field, either with your eyes or binoculars, there will usually be a lot of distracting backgrounds - foliage, earth, water etc. Your eyes have a much greater depth of field than DSLR cameras - the images in Smallshire and Swash are closer to the reality you will see in the field (and I applaud them for doing it).
Darters are small dragonflies about 3-4cm long. Immature darters of both sexes are yellowy brown with males maturing to black (Black Darter) or red colouration. Old females can obtain male colours so if you see a red darter do not assume it's a male! Conversely if a darter isn't red or black don't assume it's a female - it may be an immature male.
Mature males
Let's start with the easiest age/sex to identify - males with mature colouration. Below is an image which you can click on to get full size in a separate screen.
Black Darter mature male - a small, predominantly black and yellow, dragonfly with a distinctive (and definitive) black panel with three yellow dots within it on the side of the thorax, all black legs and black down the side of the frons, With the exception of White-faced Darter, which you would probably have to make a planned trip to see, this is the only predominantly black darter so you shouldn't confuse it with any other species.
Ruddy Darter mature male - a small red dragonfly with all black legs; black down the side of the frons; plain sides to the thorax. Note that in very mature male Common Darters the side panel becomes obscured so it is important to check the leg colour and/or frons.
Common Darter mature male - an orangey red dragonfly with a distinctive (and definitive) reddy brown panel between two yellowy brown panels on the side of the thorax; brown legs with a pale stripe down the back; black along the top of the frons but not down the side. As mentioned just above the side panel can become obscured with age in which case the stripes on the legs and/or lack of black down the side of the frons will determine that it is a Common Darter.
Red-veined Darter mature male - a red dragonfly with a distinctive (and definitive) pale panel on the side of the thorax; dark legs with a pale stripe down the back; black down the side of the frons; red over blue eyes; orangey yellow wing-bases; pale pterostigmas (wingspots) thickly bordered with black; red veins towards the costa (leading edge) of the wing.
It's worth repeating the two key features that put you well on the way to identifying a darter - they are the same for both sexes - the legs and the extent of black down the side of the frons.
Red-veined Darter is an annual regular visitor which you may encounter. Vagrant Darter is an extremely rare visitor to the UK which only a very few people will encounter (probably in the south-east of England) - you can find out about it in Smallshire & Swash or Brooks & Lewington. Yellow-winged Darters occasionally have an invasion year and appear in decent numbers. As their name suggests they have a lot of yellow in the wings and are well covered in the field guides.
As you can see from the table above if you can see black legs then you don't need to see (or get into a position to see) the black down the side of the frons to know you've got either a Black or Ruddy Darter.
Cautionary Note: Sun shining on a darter's black legs can make them appear 'striped' or much less black and that legs are often half-hidden in vegetation. Also shadows can make a Common Darter appear to have black down the side of the frons.
Black Darter
Tenerals
You are most likely to find tenerals hanging on vegetation waiting for their 'milky' wings to harden. In this position the black legs are usually apparent. Also obvious is the dark triangle on the top of the thorax and the two inverted black T's on the segments at the end of the abdomen. In the image of the female you can just see the black side panel containing the three yellow spots - present in both sexes at all ages. Note the tenerals have white pterostigmas (wingspots) - this is the case for tenerals of ALL darter species.
Female / immature male
Before the male becomes black the sexes are similarly coloured. The male has a more waisted abdomen while the female's abdomen is thicker, more parallel-sided and has more black along the sides. The features mentioned under tenerals can be seen - black legs; black side panels with three yellow spots; inverted black Ts at the end of the abdomen; dark triangle on top of thorax (just visible in the image of the male!).
Mature insects
With age the males become mostly black although you can just make out the side panel of the thorax in the image below. Females can become quite dark (but I don't have an image of one approaching male colouration!). Note that you can see the black going down the side of the frons when viewed from the side (the male image) or with a slightly more frontal view (the male).
Ruddy Darter
I won't put up any photos of teneral Ruddy Darters for two reasons - firstly, apart from the milky wings and white pterostigmas (that all teneral darters have - we saw that earlier on this page with Black Darters) they are the same as the immatures and, secondly, I haven't got any!
Female / immature male
Before the male becomes red the sexes are similarly coloured. Ignore the differences in tone of the colours in the photo below - the pictures were taken on different days, in different lighting conditions and with different cameras. The male has a more waisted abdomen while the female's abdomen is thicker and more parallel-sided and has a little more black along the sides. They have black legs; plain sides to the thorax; thick black lines on S8 and S9 towards the end of the abdomen and a dark T on top of thorax. Both sexes have black down the sides of the frons (but you will see that in pictures further down the page not in the next one).
Mature male Ruddy Darter
Males become very red - red frons (face), red thorax, red abdomen - Ruddy!
Mature female Ruddy Darter
Female darters darken with age - they can become reddish so do not assume that a red darter is a male darter.
Common Darter
Females and immature males
Before the male becomes red the sexes are similarly coloured. The male has a more waisted abdomen while the female's abdomen is thicker and more parallel-sided and has a little more black along the sides. They have striped legs; yellowish sides to the thorax with strong black lines; black lines on the top of S8 and S9 towards the end of the abdomen and small shoulder stripes on top of thorax. Black extends along the top of the frons only (viewable in the 2nd image). When viewed from the side females have a double row of dashes along the the abdomen - in the males the dashes are present on S7/S8/S9 (sometimes on S6) only - and the vulvar scale is usually visible but not prominent.
Mature insects
The pale pterostigmas of immature become reddish brown with age and the pale shoulder stripes disappear. The striped legs and extent of black on the frons are still obvious (given the right viewing angle). Males become orangey red as they mature and the middle panel on the side of the thorax becomes red making it extremely easy to pick out at distance and in flight.
Mature females become dark brown and sometimes reddish. As the insects become very mature the wings take on a brownish suffusion and in males the thorax becomes very brown so that the side panel is not obvious.
Red-veined Darter
I see quite a few 'Is this a Red-veined Darter?' posts in forums - usually by people who haven't looked up the key features of Red-veined Darter.
In common with Common Darter it has black legs with pale stripes. Unlike Common Darter the black across the top of the frons extends down the side. Immatures have a white face which becomes red in mature males. The other darters occurring in southern England have green undersides to the eyes - the blue underside to the eyes of Red-veined Darter are obvious even in teneral insects. At all ages the pterostigmas are pale and thickly bordered in black. They have yellow wingbases (more extensive than in Common or Ruddy but less extensive than in Yellow-winged Darter). Immatures and females have thick yellow veins towards the yellow costa.
Immature males and females are identified by the appendages at the end of the abdomen, the male's secondary genitalia under S2 (if you can get an angle to view it) and the female having two lines of black on the side of the abdomen while the male has only one line.
As with the other red darters Red-veined females can become red with age.
As the male matures the face becomes red and the yellow wing veins become red. A single pale panel appears on the side of the thorax. The pterostigmas become a pale orange.
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