Keeled Skimmer

Last season (2007) a couple of friends introduced me to the Keeled Skimmer (Orthetrum coerulescens). Since the mid 30’s the Keeled Skimmer (O. coerulescens) was thought to be extinct in Denmark. In 2006 a rather large population was found at Søby, Jutland. By the end of the season 2007 it was known from 4 locations. At the beginning of the species flight-period this year another location was added to the list. One of my goals this year was to find a new, hitherto unknown population.

Male of Keeled Skimmer (O. coerulescens)

While litterature states the Keeled Skimmer (O. coerulescens) to be found in all sorts of running waters, in Denmark it has so far only been found in slightly acidic bogs with runnels and pools. This appears to be so throughout its most northern range, while the more southern part of Europe, where it is more common, it can be found in all sorts of running waters.

Here in Denmark the larvae live in the acidic pools and runnels for two years before molting a final time to emerge as adult dragonflies.  The male is bright blue on the abdomen and dark with a blue shade on the thorax. The eyes are also a shade of blue. All quite befitting of the Danish name which literally translated is Small Blue Dart. The females are yellow, aging to a dull yellow-brownish colour. In Denmark it  can most likely be confused with the Black-tailed Skimmer (Orthetrum cancellatum). The easiest way to distinguish between the two are by the pterostigma; the Keeled Skimmer (O. coerulescens) has yellow/orange pterostigma where the Black-tailed Skimmer (O. cancellatum) has dark pterostigmas.

A. Yellow/orange pterostigma of Keeled Skimmer B. Dark pterostigma of Black-tailed Skimmer

I began the search behind my computer screen. First I plotted the known populations on a map, coincidentally drawing a triangle. Logic stated the most likely place to find a new population would be within that triangle, between known populations. So I went through aerial photos looking for, what looked like acidic waters, typically surrounded by heath land. I ended up with 7 areas likely to hold a population of Keeled Skimmer.

While there was a lot of other exciting plants, dragonflies and butterflies at the first 3 places, there were no Keeled Skimmers. The 4th place I had pointed out was only 10 minutes drive from work, almost on my way home.

Aerial photo and landscape photo of the location

When I arrived the weather wasn’t too good for a dragonfly hunt; overcast and windy. Still the place looked very interesting to say the least, so I went for a walk across the bog. Standing in the middle of the bog, by the edge of one of the pools a small bright blue colour darted aggressively up in front of me. Zig-zagging in front of me, pausing only to hover facing directly at me as if threatening an intruder (which I kind of was), the sight of the little blue dragonfly made my heart jump and released the adrenalin to rush through my veins. Without any thought whatsoever, I stepped out into the pool of water, sinking in mud to the knees, bashing my net about in front of me. I knew then that it HAD to be the Keeled Skimmer (O. coerulescens), but took it out of the net and checked the pterostigmas, just to be certain. Standing in the smelly acidic water soaked from my knees down, I realized that had I only paused and waited at the edge of the pool, then it would have settled shortly and I could have gone Camera Crazy on it. I released the dragonfly and luckily hovered off and settled in the vegetation, not far away. Time to take pictures!

The male Keeled Skimmer often perches on the vegetation keeping an eye on its territory. It usually flies in short spurts, hover, spurt, hover, spurt before perching again. It can often be observed returning to select favourite patches of vegetation to keep look-out.

Male Keeled Skimmer (O. coerulescens) perched on a twig

The following hours I was lucky to see several males and observe their behaviour. Fearlessly, it chased off foraging Common Hawkers (Anax juncea) and Migrant Hawkers (Anax mixta), despite them being at least twice the size of the Keeled Skimmer (O. coerulescens). I also saw a single mating wheel. They can be in the wheel up to 30 minutes before the male releases the female again. Once set free the female begins laying eggs  in small batches in the water, with the male patiently following around, hovering over her keeping guard. The eggs hatch after 5-6 weeks and the larvae feed of aquatic invertebrates for (in Denmark at least) approximately two years before finally molting to the adult dragonfly.

So the sixth population of Keeled Skimmer (O. coerulescens) was found in Denmark, and more will definately follow. We just have to look a bit closer. Most biologists will agree that succeeding in setting out to find a new population of some rare organism, by research, homework and persistence is one of the most rewarding experiences. This one will definitely stick with me for some time!

All photos displayed in this post are by Nicholas Bell (except the aerial photo).