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Endemic Invertebrates of Shetland

 

 

Some of the insects of Shetland have been reasonably well-studied, especially the moths which were the subject of much attention at the end of the 19th century when it was discovered that there were many unusual melanic (dark) forms in the islands. As well as several subspecies or varieties of moths there is a semi-endemic species of weevil of dubious taxonomy and an semi-endemic subspecies of bumblebee. The blackfly Simulium zetlandense was named for science based on a specimen from Shetland but is now known to occur in Fennoscandia.

Moths

There are five named subspecies of moths which appear to be good Shetland endemics i.e. they are not found anywhere else in the world and all (or nearly all) of the the individuals in Shetland conform to the characteristics of the named subspecies.

Eupoecilia angustana thuleana A small tortrid micro-moth which is common in grassy areas on Unst, Yell and Mainland and which flies in June and July It was originally described as a new species. It is much more heavily marked than the nominate subspecies which is found in the rest of Britain.

Red Carpet Xanthorhoe decoloraria hethlandica. A common  geometrid moth found throughout the islands, usually recorded at light at night from June to October, but mainly in July and August. The Shetland race is orange-brown in colour and not white and dull red like the subspecies found in the rest of Britain.

 Photo by Dave Hall.

Silver-ground Carpet Xanthorhoe montanata shetlandica A common geometrid moth found throughout the islands, sometimes found flying by day, but most often recorded at light at night. It is particularly common in the northern isles of Shetland. It flies from June to August. The Shetland race is slightly smaller than the Mainland race, usually with a less distinct bar.

Photo by Micky Maher.

Netted Pug Eupithecia venosata fumosae A locally frequent moth, found in the vicinity of beaches throughout the islands, wherever the foodplant Sea Campion Silene maritima is found. It flies in May and June but is rarely seen unless traps are run close to beaches, although larvae (caterpillars) are easily found by examining Sea Campion seed pods. The Shetland subspecies is darker than the form on the British Mainland. It is probably endemic to Shetland but moths resembling this race are occasionally found in Orkney.

 Photo by Micky Maher.

Grass Rivulet Perizoma albulata subfasciaria  A locally common but probably declining geometrid moth found throughout the islands, except Fair Isle. It is usually seen by day around the food plant Yellow Rattle Rhinanthus minor and is seen from June to August. The Shetland race is smaller and darker than the race found in the rest of Britain.

Photos by Steve Minton.

Four more named subspecies appear to form at least the majority of the Shetland population, but are also found elsewhere. It may be that populations elsewhere are best regarded as belonging to different subspecies. This is because it is likely that the taxon (in this case subspecies) present in Shetland would be paraphyletic - in other words, the populations have different origins and do not share a common ancestor which separate them from other races. Modern taxonomics would make this treatment untenable and, if that is the case, then they should be treated as separate races.

Ghost Moth Hepialus humuli thulensis A common moth found throughout the islands, except Fair Isle. Most males are dark, sometimes exceptionally so, although pale specimens also occur. The species flies from May to August, but mainly July, and it may often be seen flying at dusk in the 'simmer-dim' (summer nights). Larvae (caterpillars) feed on roots, possibly for up to two years, and are frequently dug up in gardens. The moths found in the Faroe Islands are also included in thulensis and, in this case, it is possible that Faroe was colonised via Shetland, in which case common ancestry is possible.

Photos by Steve Minton, Roger Riddington.

Yellow Shell Camptogramma bilineata atlantica A frequent, but very local, moth found on on Mainland, Muckle Roe, Fair Isle and Unst. It flies from June to August and may be seen by day or attracted to light. The race atlantica , which is darker and duller yellow than the Mainland British form, is also said to occur in the Outer Hebrides, but it seems unlikely that these two populations share a common ancestor.

Dark Marbled Carpet Chloroclysta citrata pythonissata A locally frequent moth throughout the islands, except Fair Isle. It may be seen by day or at light from July to September but mainly in August. The Shetland race is also found in Orkney and, as Shetland was probably colonised via Orkney, common ancestry is likely.

Photo by George Petrie.

The Exile Apamea zeta [exulis?] A locally common on moorland on Mainland, Muckle Roe and Unst; one undated record from Yell and an unconfirmed record from Fair Isle. It flies in July and early August and is attracted to light or sugar. It was originally thought to be endemic species, Apamea exulis, but it was then regarded as being part of a widespread species which includes the Northern Arches Apamea zeta assimilis, which is found in northern Scotland. Most recently, the Shetland population has lost its status as an endemic subspecies and has been treated as the only British population of the widespread Scandinavian subspecies A. z. marmorata. Some authorities, including Dr Svend Kaaber who has seen the species in Denmark, Faroe and Shetland, still believe that the Shetland population deserves subspecific status.

Photo by Wendy Dickson.

Five more species have named forms which are only found in Shetland (two currently recognised as subspecies), but as these are often found alongside typical individuals and they often only form a small proportion of the population, they can be regarded as no more than forms or varieties. There are, in fact, some other forms which are arguably as distinct as some of these named forms, but none have official names.

Map-winged Swift Hepialus fusconebulosa f. zetlandicus A common moth found throughout the islands, often seen flying at dusk or attracted to light, mainly in June in July but recorded from May to August. The Shetland form, which is bright and variegated, only  forms a small proportion of the population and is one of three forms found in the islands.

Photo by Mike Pennington.

Garden Carpet Xanthorhoe fluctuata f. thules A frequent moth  throughout the islands and the only Shetland macromoth with a regular second brood. Consequently it can be found from April to September. The Shetland form is a dark melanic but a melanic form is also found in towns and cities on Mainland Britain and it only forms a small proportion of the population in Shetland.

Twin-spot Carpet Perizoma didymata [hethlandica?] A locally common but declining moth found throughout the islands and flying from July to September. Although still accepted as a named subspecies, browner and duller than the Mainland British race, moths of this form only seem to constitute a small proportion of the Shetland population, so the race is not really valid.

Photo by Rob Fray.

Autumnal Rustic Eugnorisma glareosa f. edda A common  throughout the islands, usually found at light and recorded in August and September. The dark form edda is also occasionally found outside Shetland but it is commonest in the islands where it increases from less than 5% of the population in the south Mainland to over 95% on Unst.

Photo by Mike Pennington.

Ingrailed Clay Diarsia mendica [thulei?] An abundant moth found throughout the islands, from June to October but mainly in July and early August. A highly variable species, moths conforming to the description of the Shetland subspecies form only a tiny part of the population, so the race is not valid. .

Beetles

a species of weevil Protapion ryei (= Apion reyi ) A tiny weevil which feeds on the flowerheads of Red Clover Trifolium pratense. It was formerly thought to endemic to Shetland but is now believed to be present in Orkney and the Inner and Outer Hebrides. It may not be a valid species but the extreme end of a cline (a gradual change over a long distance) and therefore part of the species Protapion assimile, a common species throughout Britain.

Bumblebees

Small Heath Bumblebee Bombus jonellus vogti Scarce on moorland on Mainland, Muckle Roe and Unst at least, flying from April to September. The race breeding in Shetland has a yellow tip to the abdomen, rather than the white tip found in most other races.

Photos by Mike Pennington.

Shetland Bumblebee Bombus muscorum agricolae Very common throughout the islands, flying from April to October. It is much more colourful than its mainland British counterpart (which is known as Moss Carder Bee), with a bright orange thorax and a yellow abdomen. It is also said to occur in the Outer Hebrides, but it seems unlikely that these two populations share a common ancestor, so it may be best to separate the populations as different subspecies under the rules of paraphyly.
 
Photo by Hugh Harrop.
Bibliography
Johnston, J. L. 1999. A Naturalist's Shetland. T & A. D. Poyser, London.
Waring, P., Townsend, M & Lewington, R. 2003. Field Guide to the Moths of Great Britain and Irelamd. British Wildlife Publishing, Rotherwick.

 

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