Glasgow & SW Scotland Butterflies

Glasgow & SW Scotland Branch Website

January 7, 2009

A second brood of the Iron Prominent in the Glasgow area?

Filed under: Moths — Tags: , , , , — Scott Shanks @ 12:34 am

The Iron Prominent (Notodonata dromedarius) is a furry medium-sized moth with distinctively marked dark grey-brown forewings with rusty-brown streaks.  According to Waring & Townsend, the species is widely distributed throughout the UK, however the distribution map on the NBN gateway site suggests it’s largely absent from south west Scotland. Individuals in northern England and Scotland often have a darker ground-colour with fainter markings.

Iron Prominent on my thumb

Iron Prominent on my thumb

In the south of Britain there are usually 2 generations per year, with adults flying in May-June and late July-August, while in the north of Britain and Ireland there is a single generation each year with adults flying June-July…at least that’s what it says in the books!

While trapping at SWT Loch Ardinning (Just north of Glasgow) on the 30th of August 2008 I had an Iron prominent come to the light of my 15W actinic heath trap. (NS569777 ). It was a feisty wee thing and took ages to settle down, causing total havoc as it disturbed the other moths in the trap. I think that’s why one of its wings looks so badly worn.

Iron Prominent moth

Iron Prominent moth

 

 I passed this record to John Knowler the vice county moth recorder for Stirlingshire, who replied had he’d also had a late Iron prominent come to light.  It looks like the Iron prominent may have had a partial second brood in Scotland during 2008.

Could this be a response to global warming? According to BBC weather records for 2008, temperature records in Scotland were a degree or two above average during both July and August. It was also wetter than usual once more! Could it be that this small increase in temperature is enough to trigger a biochemical response in larvae or pupae that aborts the usual ‘hibernate’ signal, and leads to accelerated development of larvae or early emergence?  

The Iron prominent can be found in broadleaved woodlands, heaths, wet carr, riverbanks and occasionally gardens. The pale green caterpillar has a brown stripe along its back, with humps on the 4th-7th and 11th segments of its body. It can be found feeding on birch and alder, and occasionally hazel or oak. The Iron prominent overwinters as a pupa in a flimsy cocoon under the soil. Supposedly the caterpillar is quite easy to raise in captivity if supplied with fresh vegetation every few days, but should probably be returned to the wild before it pupates to maximise the chance of the adult’s emergence coinciding with a suitable mate the following year.

Certain montane invertebrate species can exhibit delayed larval development in cold and wet years, which prevents the population being wiped out if the adults emerge during inclement conditions and fail to breed. The ability to produce additional generations when conditions are good may be another aspect of this phenomenon?

Does anyone else have other ‘late’ records of the Iron prominent in Scotland? Was this a local event or was it nationwide? It’s likely that other species may be responding to temperature increases in a similar way. Perhaps we could compile a list of species that are taking advantage of climate changes to produce further generations during the year? Such species may prove useful as biological indicators of wider habitat and environmental changes happening around us that we should ‘keep an eye on’ in the future.

Feel free to add any sightings, comments or thoughts below. :)

Scott

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