Jun 222021
 
  1. Background

The Irish Red List on Macro Moths (2016) has the following to say about the Thrift Clearwing moth (Pyropteron muscaeformis)

I have been studying the sod hedges on Loop Head for several years, principally to assess the solitary bee populations that they support. I have also been aware of the decline of the Thrift Clearwing moth in Ireland. It seemed to me that if you want to find something rare that feeds on thrift, then go where there’s the most thrift, so I have also spent some time in recent years looking for this insect there. Until this year, I was unsuccessful: probably I had been looking too late (early – mid July).

On Saturday 29th May 2021, I discovered a female Thrift Clearwing moth calling amongst the thrift in the sod hedges, close to the Grave of the Yellow Men. If the Red List account is still current, this is only the third record since 2000. The location is 150km from the ‘recent’ west Cork records and, even taking into account the pre-2000 data, is a new one.

On foot of this find, I obtained a pheromone trap and lure for Thrift Clearwing, and twice returned to the area to do a more systematic survey. A visit on Sunday 13th June was thwarted by bad weather, but a return on Friday 18th June yielded moths at all three of the survey sites that I had selected.

  1. Survey Details and Results

Based on my initial find, I identified three sections of sod hedges to survey:-

A – Kiltrellig: along the coast road west, north of the bridge at Cloghaun Lough. Map Ref. Q752483. This is also where my initial find was;

B – Kilclogher: along the coast road east, south of the bridge at Cloghaun Lough. Map Ref. Q759481;

C – Kilbaha south: along the approach road to Loop Head lighthouse, and the track northwards to the cliffs. Map Ref. Q699476.

The pheromone trap consisted of a small cage to hold the lure (a rubber bung that had been soaked in the pheromone chemical), located above an ingress area and a funnel leading to a collection pot. The trap was set up at the mid point of each location, being suspended near the top of the sod hedge, so that it hung down amongst the thrift plants. It was left in place for 40 minutes (research on-line suggested that 40 minutes was reckoned by regular users of pheromone traps to be sufficient time to get a catch, if the subject insect was present in the area). The trap was then checked.  The results were as follows:-

Location Date No. Moths
Trap Casual Observation
A 29/05/2021 n/a 1 calling female
A 18/06/2021 4 males n/a
B 18/06/2021 2 males n/a
C 18/06/2021 0 1 calling female, 1 male attending

I was particularly struck by the success at location C, which was on the more exposed, north-facing side of the peninsula. The general numbers of insects active here were far lower than the comparatively sheltered locations A and B, which were busy with bees, wasps, hoverflies and other Diptera. Site C is also, relatively speaking, inland. At site C, the two moths were not caught by the trap but were a casual observation nearby. Since one was a calling female, it was likely in competition with the trap for males.

  1. Conclusions

Based on the outcome of this small, informal survey, one can make the following observations about the status of the Thrift Clearwing moth in Ireland:-

  1. Given the scale of this find at Loop Head, it is reasonable to assume that there are undiscovered populations of Thrift Clearwing moths at suitable locations elsewhere in Ireland;
  2. The Critically Endangered status afforded the moth on the 2016 Irish Red List may be unduly pessimistic;
  3. The received wisdom of the moth’s apparent preference for stressed host plants in the splash zone is, at best, not the whole story, at worst, somewhat misleading;
  4. There is a good case for planning and executing a wider survey of candidate sites, using pheromone traps;
  5. The key criterion for site selection should be that there is a large amount of thrift present.

Photographs

The calling female from location C

General view of the sod hedges at location B

Three of the four males trapped at Location A

Thrift Clearwing male from location A

Trap set up at location C

Nick Larter. Ennis, Co. Clare.

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