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Nature in Shetland

winner of a Shetland Environment Award 2004

Shetland Entomological Group

 

Only six species of lacewings have been recorded, probably all as immigrants. Most records are unpublished but records from the 19th century come from King (1890).

Migration of Neuroptera is poorly understood. The following article appeared in Neuro News in 1995.

It has not been updated.

 

IMMIGRATION AND NEUROPTERA IN SHETLAND

Mike Pennington

Shetland is Britain's most northerly land mass, consisting of an archipelago of 14 inhabited and hundreds of smaller islands. Most of it lies above 60^O N, while the nearest railway station is in Bergen and the nearest capital city is Oslo. Indeed, Shetland belonged to Norway for many centuries and a Nordic influence is still evident. This Nordic influence extends to the insects, especially migrants.

As to the Neuroptera (the other orders covered by the Neuroptera Recording Scheme have not been recorded in Shetland), our only common species is the ubiquitous Chrysoperla carnea. I have to admit that I have not systematically collected records, so the following comments are necessarily generalised. It seems most likely that carnea only occurs in Shetland as a migrant, looking at records from the last three years.

In 1992 there were no records in early summer (despite several records of migrant Lepidoptera), but there was a reasonable influx from July onwards. These records appeared to follow an influx of aphids - certainly Nick Riddiford on Fair Isle recorded unusual numbers of aphids there. At the end of 1992 there were many carnea seeking hibernation sites indoors at Baltasound on Unst and in peat-stacks at Gutcher on Yell (A. Gear) and at Eswick on Mainland (T. Rogers).

The only June record I have in recent years comes from 1993, and I wonder if this was a successfully hibernated individual following the 1992 influx. As I understand it mild, wet weather is the least likely to lead to successful hibernation by adult insects because fungal infections are more likely. Typical Shetland winters are mild and wet with little snow and lots of rain. The scarcity of spring records in Shetland suggest overwintering is rarely successful here. The rest of  1993 was a poor year for insect immigration and the only other record  of carnea I have from that year was on Foula on October (F. Ratter), presumably a migrant.

In 1994 there was a massive influx of Lepidoptera and hoverflies (Syrphidae) in early July and several carnea were recorded at this time. Further Lepidoptera immigration in early August lead to further carnea records scattered around the islands and including records from the two remotest localities - Foula (F. Ratter) and Fair Isle (N. Riddiford). Lacewings continued to be seen through the autumn with insects again seen indoors at Baltasound at the end of the year. There was no obvious sign of an aphid invasion in 1994.

In summary, Chrysoperla carnea appears to be a migrant in Shetland, recorded from July onwards but usually failing to overwinter. It is also worth recording that hibernating specimens have included both green and brown forms.

The origins of the migrant carnea are also open to discussion but I would suspect that Scandinavia is as likely a source as anywhere. The lacewings of early August 1994 were associated with an influx of migrant moths that included species most likely to have originated in Scandinavia. Incidentally, carnea has been recorded from Faroe, another 300 km north-east of Shetland. There are 11 records of specimens brought to the Faroese Museum of Natural History in September to November (D. Bloch and H. Mourier, 1994. Pests recorded in the Faroe Islands, 1986-1992.  Fróðskaparrit 41. bók. 1994 (1993): 69-82).

Five other species of Neuroptera have been recorded in Shetland. In the summer of 1889 J.J.F.X. King (1890, Neuroptera from the Island of Unst Ent. Mon. Mag. 26: 176-180) recorded Hemerobius simulans, Wesmaelius nervosus and Wesmaelius subnebulosa at the Halligarth plantation on Unst, as well as Chrysoperla carnea, of course. W. nervosa was recorded there again in 1994, as well as at Eswick on Mainland (T. Rogers). W. subnebulosa was also recently recorded, on Yell in 1990 (B. Laurence). Two further species were recorded at Eswick by Terry Rogers in July 1994 - Hemerobius humulinus and Hemerobius lutescens.

What is the status of these species? Well, there are virtually no native trees left on Shetland and most plantations have recent, post-war origins. Records of the same species at Halligarth over 100 years apart might suggest a species is resident there. However, I have visited the site regularly over the last seven years and I have never seen anything resembling a brown lacewing before, yet I saw three in 1994, a good migrant year. The Hemerobius species at Eswick were first recorded on 5th July 1994. On this day Shetland was smothered in Red Admirals Vanessa atalanta, Diamond-back Moths Plutella xylostella, Silver Ys Autographa gamma and the hoverflies Metasyrphus corollae and Episyrphus balteatus. Terry Rogers is also adamant that there have never been brown lacewings in his garden before but in 1994 there were dozens, presumably attracted by an infestation of aphids on the trees there (aphids which have built up over recent years rather than arriving in 1994).

Then there is King's record of H. simulans at Halligarth last century. This species is associated with conifers, none of which are planted in the Halligarth plantation (or anywhere else on Unst last century), although there is the possibility of incorrect determination in this case. King was convinced that the Neuroptera he found had been imported with the shrubs as he found them nowhere else on Unst (and presumably simulans' association with conifers hadn't been established in his day). However, the trees at Halligarth had been planted for almost 50 years at the time of King's visit - a long time for a population to survive in a tiny area of habitat (Halligarth is about 100m x 100m in area). King also noted that the summer of 1889 was exceptionally fine, conditions which I would associate with insect immigration.

So, are all these species migrants? Obviously it is too early to say, but as we collect records over the years a clearer picture may emerge. Now we know what we are looking for we can search more intensively for brown lacewings during periods without insect immigration to see whether Shetland has any resident Neuroptera. Certainly some species may be catholic enough in its tastes to maintain a foothold in the islands. However, I wonder whether any species recorded could survive in a group of islands where virtually the only trees are a few scrawny willows, sycamores and conifers.

Finally, while I have acknowledged recorders in the text where appropriate, I must add our appreciation of the efforts of Colin Plant in identifying our specimens and encouraging our interest.