The Black Darter

The Black darter, Sympetrum danae, our smallest native dragonfly, at about 4cm long, with a wingspan of about 5cm, is our only black species. It can be spotted skittishly darting about our moors at the moment, seemingly going from zero to a hundred and back in a split second as it strikes out to snatch prey, returning to its previous position where it discreetly sits, watching and waiting, to ambush its next victim.

Aerial agility

Like all dragonflies, the Black Darter evolved to be such an expert aerial predator because it has the ability to move each wing independently, giving it the flexibility to hover, take off vertically and even fly backwards. This aerial agility enables it to catch its prey in flight, and it can out-manoeuvre pretty much any other airborne creature as it hunts for flies, midges and other flying prey. I have seen them evade such expert avian predators as the Swallow and the Merlin, which you might otherwise expect to be capable of catching just about anything.

At home on the fells

It prefers wet and boggy habitats with rushes and other low vegetation to perch on , but needs plenty of sunlight in which to bask and warm itself up, as, like other dragonflies, they will only fly if there is less than 30% cloud cover and in their adult form they can only catch prey in flight so they can starve if the conditions are too dark or rainy for them to fly. Water quality itself is important as this species will only breed in cool, acidic bog pools which do not become stagnant at all in any stage of its lifecycle.

Lifecycle

The black darter, like all dragonflies, has a two-stage life cycle, although most people only see it in its adult stage. It starts life as an egg, deposited beside water by the female around late summer, the eggs, laid in clutches of up to 200, then overwinter until hatching next spring.

Dragonfly larvae are known as ‘nymphs’ (or ‘naiads’ in America) and the nymph of the Black Darter is one of the smallest to be found in the British isles, despite their diminutive size they are as fiercely predatory as the adult. Feeding predominantly on midge larvae, water fleas and other small aquatic invertebrates they grow quickly, with the nymph stage only lasting from 3 to 6 months, compared to the nymph stage of other species of dragonfly which can last as long as 5yrs.

The nymph passes through a series of moults as it grows, shedding its exoskeleton each time as it outgrows its own skin, until it reaches the final stage, when the nymph, called an ‘instar’ at this point, will have grown to a whopping 2cm in length. The instar, which is already showing some resemblance to the adult form with visible wing nubs showing, then climbs up a nearby piece of vegetation to shed its last larval skin, which is known as an exuvia.

The Black Darter is one of the last dragonflies to emerge and this usually takes place around July and August, although the period when adults are emerging can extend until October. The newly-emerged adult has to wait until its wings are fully unfolded and its body has expanded and dried out properly before flying for the first time and as with other species like the Brown Hawker, which I wrote about here in an earlier article, this is when it is at its most vulnerable.

If they survive past this stage without being being snaffled up by a Frog, Heron or other opportunistic creature they become fully fledged predators in their own right and take off to chase prey as soon as they are able. As adults they are fairly squat for a dragonfly and have a vaguely spider-like body-shape, with a head that tapers back to the thorax, in length they are only about 3 to 4 cm and have a wingspan of 4 to 5 cm.

They still have a lot of maturing to do though in their short lifetime and don’t fully mature until about 2 or 3 weeks later, by which time they should have mated. In some cases adults will hibernate through the winter and fully matured adults have occasionally been recorded in April, which is well before any will even have emerged that year.

Appearance

Both male and female have clear wings with a black wing spot, and mature males are all black except for yellow markings on the abdomen and yellow stripes on the thorax, they also have bicoloured eyes which are black above and an olive green below. The female looks quite similar to the immature male, with both being yellow-brown, however the immature male has a waisted abdomen and the mature female has dark yellow patches at the base of her wings and bicoloured eyes, which in the female are a reddish-brown above and olive below.

Threats

This species is common throughout the British isles on heaths and moorland, although it is rarer in the eastern side of the country due to the dryer climate, however it is facing some of the threats which other species found in these habitats are endangered by.

These include;

climate change

Increasingly heavy and erratic rainfall, and longer and hotter dry spells can change and destroy their fragile bog pools quicker than they can adapt.

Drainage and improvement for agricultural purposes

Here in the northwest numbers of this species dropped after large areas of the moors were drained from the 60s through to the 80s for the purpose of land improvement for agriculture. This was mainly carried out by upland farmers to claim payments, but as a much needed source of money it ceased in the 90s and now it is very much the opposite case, with landowners being paid to block up drainage ditches and flood parts of the moors instead, which, if done properly and this water isn’t allowed to become stagnant, should benefit the Black Darter and other species reliant on peat bogs.

Forestation

Extensive forestry plantations have also destroyed much of our uplands and heathland over the decades and in many areas large expanses were drained for this purpose, although this too is now understood to have been massively destructive. In Bowland and other parts, where Grouse shooting is one of the main uses of the land, the moors escaped any large scale forestry, with only a few plantations to be found in the area such as those behind Dunsop bridge, around Stocks reservoir, and a couple on the fell sides above Chipping.

Any schemes for planting large areas of the moors with native trees, in an aim to restore the ancient wild woods which existed in prehistoric times, should be weighed against the threat this would pose to the rare and fragile habitat that species such as the Black Darter, which could well be facing additional threats in the future, rely upon.

A B-H