Monday, August 27, 2012

The Rarest Dragonfly in Ireland

Immature Male Downy Emerald, Cordulia aenea
The rarest of Irish dragonflies is the Downy Emerald (Cordulia aenea), a glorious, metallic green coloured odonate with a clubbed abdomen. While it is common in Britain and other parts of Europe, C. aenea can only be found in a handful of locations in Ireland, all clustered around the Kerry/West Cork region of the country. Even then, it is only encountered near water bodies that are in close proximity to ancient oak woodlands, specifically areas near Killarney and Glengarriff national parks (1).
 
Immature Male Downy Emerald, Cordulia aenea
I was lucky enough to see and photgraph an immature male at one of these locations recently, something which surprised me quite a deal as they are recorded as emerging in late May, with peak occurrence in mid June. However the wet and windy summer that we have had here may account for this odd timing. The individual pictured was seen on a rare sunny day in Glengarriff Woods Nature Reserve, near Dromdour Lough. Glengarriff Woods is the only location outside of Killarney in Ireland to hold a population of C. aenea (2). Incongruously, however, Dromdour Lough is actually not within the boundry of Glengarriff Park and is in fact within a commercial conifer plantation owned by Coillte, the Irish state sponsored forestry company. Apparently there is a long term aim to recreate the native oak woodland in the area once commercial felling of the mature crop of conifers in complete, something which would very much benefit the population of C. aenea as there is a positive association between this species and woodland, which seemingly provides a feeding habitat for adults (1).
 
Immature Male Downy Emerald, Cordulia aenea
The individual seen was, as mentioned previously, an immature male and as such lacked the vibrant green colour that is indicative of the species. It was photographed at rest on a wooden railing at the side of a path next to Dromdour Lough and was seen to behave aggressively and chase a male Common Darter (Sympetrum striolatum) which also happened to rest on the railing. This activity continued for at least five minutes, after which the male C. aenea flew off across the lake.

References:
  1. Nelson and Thompson, 2004. A Natural History of Ireland's Dragonflies pp. 226-235
  2. DĂșchas, 2002. Glengarriff Woods Nature Reserve information leaflet

3 comments:

  1. I love dragonflies. They are among my favourite insects. However I am not as good to identify them (=not good at all) as I am with butterflies.
    This aggressive behavior against other species is interesting, isn't it? What could be the reason?

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  2. Identifying them can be a bit of a chore alright, but here in Ireland we don't have a huge numbers of species (32 in all, but only 24 of those are confirmed as resident) so it is straightforward enough with some (a lot) of practice. The aggression is very interesting and seems to be linked to mating. When male Downy Emeralds that hold a territory clash with interlopers, they are the ones who invariably win the clash (see Brooks et al., 1997, Journal of the British Dragonfly Society 13, pp. 52-57). Males will also grasp passing females on the wing, so the behaviour would lead to more matings.

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  3. As part of the bioblitz in the Burren yesterday, we found what looked very much like a Downy Emerald nymph in the lake at Gortlecka. If this is a case of mistaken identity, can you suggest what other species it may likely have been?

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