by Charles S. Elton (1925)
[[p. 289]] 1. Introduction.
This paper contains various observations made by myself and other members of the Oxford University Expeditions to Spitsbergen, during 1921, 1923, and 1924. I wish to thank the following gentlemen, who have kindly given me much information and other help: Messrs. F. G. Binney, W. B. Carslake, H. M. Clutterbuck, F. A. Montague, K. S. Sandford, members of the Oxford sledging parties in 1924, who gave me the data about flies and Aphids on North-East Land; Mr. J. E. Collin, for identifying the flies; Mr. F. Laing, for identifying the Aphids; Mr. E. Koefoed, for notes on flies observed on Hope Island in 1924; Mr. Krogness, for allowing me to consult the weather charts for August 1924, while I was in Tromso; Dr. Otto Stapf, for information about the distribution of the spruce in Europe. Finally, I wish to express my thanks to Professor E. B. Poulton, for his kind help and encouragement during the preparation of this paper.
2. THE SCANTY INSECT FAUNA OF SPITSBERGEN.
The insect fauna of Spitsbergen is remarkably poor. There are only two orders of insects which are present in sufficiently large numbers to provide food for other animals. These are the Diptera (flies, gnats, etc.) and Collembola. The former are mostly Chironomids, with aquatic larvae. In addition to these (see 7) there are three species of beetles, a moth, a sawfly, several species of parasitic Hymenoptera, a caddis-fly, an Aphid, and a certain number of bird and mammal parasites (lice, fleas, and bird-lice). Now the [[p. 290]] poverty of this fauna is not only due to its high arctic character, but also to the geographical isolation of Spitsbergen, as a comparison with Greenland in regions of similar climate will show. One notes, for instance, the complete absence of bees, butterflies, and Tipulid flies in Spitsbergen. The recent geological history of the Spitsbergen archipelago appears to be as follows (see Nansen, 6): the islands were connected to each other and to the continent of Europe by land before the Pleistocene Ice Age, when all these regions sank much below sea-level, with the result that Spitsbergen became isolated from Europe by the Barents Sea. This isolation has remained to the present day. At the time of maximum glaciation the preglacial flora and fauna was wiped out by a thick covering of ice, such as still exists on North-East Land. When the ice retreated, the islands were entirely barren, and inasmuch as there has been no land connection with Europe since that time, the present flora and fauna must have reached them by other means. That this conclusion is correct is shown by the striking gaps in the mammalian fauna of Spitsbergen. The lemming, arctic hare, ermine, and musk-ox are absent, and the only true land mammals are the arctic fox and the reindeer. The last two are known to make long journeys over the sea-ice in winter (in fact it has been proved--see 5--that the Spitsbergen reindeer has come over from Asia), while the other animals do not. There is thus a close analogy between Spitsbergen and Krakatoa, the former having had its flora and fauna blotted out by ice, and the latter by volcanic lava. In both cases the question arises: How has the new fauna got there?
3. METHODS OF DISPERSAL.
There are several methods by which insects might reach Spitsbergen:--
1. Wind, or flight, or both.
These factors will be considered in turn.
1. Wind, or flight, or both.
(a) Hover-flies and Aphids on North-East Land, August 1924.
[[p. 291]] North-East Land is the second largest island of the Spitsbergen group; it is about the same size as Wales, and is almost entirely covered by a thick ice-cap, which rises to some 2300 feet above sea-level. There are patches of barren rocky land round the coast, which possess an exceedingly scanty fauna. The only insects which live on this coast area are a few flies and Collembola.
A very curious case of dispersal on a large scale was met with by the Oxford sledging parties on the ice-cap of North-East Land in August 1924. I myself was not sledging and am therefore indebted for the following facts to members of the various parties, viz. Messrs. F. A. Montague and W. B. Carslake of the Northern Party, Messrs. H. M. Clutterbuck and K. S. Sandford of the Central Party, and Mr. F. G. Binney of the Southern Party. It is worth while giving the detailed experience of these parties, although exact localities, distances and heights are not yet available. (For the present purpose extreme accuracy in these data is unnecessary.)
Northern Party. August 6th. The party were camped on the top of the North-East Land ice-cap, i.e. on the N.W. corner of the island, at about 2300 feet above sea-level. There had been light south winds earlier in the day, but at 10 p.m. a strong gale sprang up from the south, and lasted six hours.
August 7th. They were still in the same place, and there was mist and fairly brisk rain with a strong south breeze.
August 8th. The party started to travel towards the south (over old ground traversed a few days before), and after they had gone about two miles, reaching a long south slope, a large black Aphid was seen sitting on the snow. After this, Aphids were met with all day on an eight-mile march south, about one to every thirty or forty yards, either on the level or on a slight south slope. They were resting on the surface of the snow, not buried, and with the wings mostly dry, about 80 per cent. being alive. Specimens of these were collected. During the day one large yellow and black hover-fly was also seen and collected; it was walking on the snow, with the wings more or less dry. Later in the day another hover-fly was also seen, but was rather bedraggled. One specimen of some large Tipulid fly was seen by Mr. Carslake on the snow. The weather during this day was cold, damp, and misty.
[[p. 292]] August 9th. During this day the party marched five miles south, still high up on the ice-cap, and they saw black Aphids still, but about one-third as thickly, and about 90 per cent. dead. There were no hover-flies.
August 10th. No more insects were observed, and during the day a blizzard came on, which lasted until August 13th. This must have destroyed all the insects.
Central Party. August 5th. The party was encamped near the head of Wahlenberg Bay, a deep fjord running into the west coast of North-East Land; they were about fifteen miles from the north side of the Bay and about 1000 feet up on the ice-cap. (Camp 9 = "Amen Camp.") At this time there were no insects on the snow.
August 6th. A reconnaissance was made, and they returned to camp by 1 p.m., no insects having been seen during the morning. There was a wind from the S.W., and the barometer was falling.
August 7th. Still at Amen Camp. Wind from the S.W. Barometer falling very low. Heavy rain on the night of the 7th.
August 8th. At 1 a.m. Mr. Clutterbuck went out and saw one yellow and black hover-fly sitting on the snow, and secured it. At 7 a.m. the party started to return in a westerly direction along the side of the ice-cap, still at about 1000 feet. Large numbers of hover-flies and black Aphids were seen during the whole of that day, on a march of from five to ten miles. The insects were sitting on the snow, alive but rather sluggish. Another hover-fly and some Aphids were collected. The wind was now rather indefinite.
August 9th. Starting from "Blue Lagoon Camp" (No. 10) the march was continued, but no more hover-flies were seen, although there were still a few black Aphids about.
August 10th. The party left "Ice Cone Camp" (No. 11) in the morning, and saw no more insects. At 2 p.m. they were stopped by a blizzard which lasted for three days, and must have destroyed all the insects.
Southern Party. On the early morning of August 7th (midnight to 8 a.m.) no insects were recorded by Mr. Binney. But while marching at the same time on the 8th (12.30 to 8.30 a.m.) both yellow and black hover-flies and black "flies" were seen. The latter were obviously the Aphids, although no specimens were collected. The place where the insects were seen was on the top of the ice-cap some miles [[p. 293]] from the east coast, between Isis Point on the East Coast and Wahlenberg Bay on the west.
I should like to emphasise the fact that these sledging parties were travelling under exceedingly strenuous conditions and over very bad surfaces. This made the collection of specimens and taking of notes no easy task. Therefore the careful and scientific way in which the data about these insects was recorded reflects great credit on the men who did the work.
Base Camp. I myself was working on Reindeer Peninsular, Liefde Bay, North Spitsbergen (about forty miles from North-East Land), at this time, and observed no hover-flies or Aphids in a long day's excursion on August 8th. Therefore the fly swarms must have passed to the north-east or else at greater heights.
It is clear from the facts detailed above, that the insects must have arrived on the ice-cap some time during August 7th. All the observations agree with this conclusion. The numbers of these flies and Aphids must have been enormous, running into hundreds of thousands or even millions, for all three parties to have seen so many at the same time. The insects appear to have been blown in a broad belt over the island. Now, where did they come from and how did they get to North-East Land?
The hover-flies (three females) have been identified by Mr. Collin as Syrphus ribesii Linn., which is widely distributed in Europe, occurring, amongst other places, in the extreme north of Sweden and in Iceland, but has never been recorded from Spitsbergen or Greenland. The Aphids are winged females, and have been identified by Mr. Laing as Dilachnus piceae Pz. (nec Walker), the food-plant being the spruce, Picea (P. excelsa, etc.). Mr. Collin informs me that although there are no actual records of the larva of Syrphus ribesii preying upon this Aphid, it is quite likely that it does so. It is only reasonable to suppose that the hover-flies and Aphids came from the same district, in view of their vast numbers and the almost complete absence of other insects in the swarms.
There are no large Tipulids in Spitsbergen. The only Syrphus occurring in Spitsbergen is S. tarsatus Zett., which lives in a few favoured spots on the west coast of West Spitsbergen (2). With it is found a small species of Aphid (not Dilachnus piceae). We know from the work of foreign naturalists in Bellsound and Icefjord, and the ecological [[p. 294]] survey carried out by the Oxford Expeditions in Icefjord and other parts of Spitsbergen, that there are no places where S. ribesii or D. piceae do or could occur. The fact that there are no trees proves that D. piceae must have come from some other country. To Dr. O. Stapf, through Professor Poulton, I am indebted for the following information about the distribution of the spruce in Europe:--
"The northern Picea of Scandinavia and Russia is P. obovata, which is treated by some as a variety of P. excelsa. Its northern limit runs from Saltdalen in Norway (67° 10' N.) over the Sultjelma to the upper Muonio river and thence to Lake Enare and the Kola Peninsula, but there is an outpost in the Varangerfjord (69° 30' N.) and another at Karasjok (68° 30' N.). Neither of these outposts is likely to supply those 'immense numbers' of the Aphid you speak of, nor is it likely that they came from the Norwegian coast at Saltdalen or the Swedish stations. At Saltdalen, at any rate, there are only a few trees of it. The tree is much more common in the Kola Peninsula (say at 67° N.), and I would suggest this to be the origin of the Aphid. It does not occur in Novaya Zemlya, which would be perhaps a little nearer."
It is probable then that the Aphids, and therefore presumably the Syrphi, came over from the Kola Peninsula to North-East Land, a distance of over 800 miles in a straight line. This idea is confirmed by the following facts about the weather conditions prevailing at this time over Spitsbergen, the Barents Sea and North Europe. During August 6th, 7th, and 8th, there was a very large depression which moved over Spitsbergen from the Atlantic. As a result of this there were strong south and south-east winds blowing from Europe over Spitsbergen and more especially North-East Land. This is precisely what would be required to carry the flies from Kola Peninsula to North-East Land. Mr. Krogness, of the Tromso Geophysical Institute, kindly allowed me to consult the synoptic charts for these days, and from the wind directions and forces it appeared that the insects would take from twelve to twenty-four hours to do the journey.
This view of the track followed by the insects is confirmed in an interesting way by Mr. Koefoed, who was engaged on fishery research in the Barents Sea in 1924. On August 13th Mr. Koefoed was able to land on Hope Island, a small, rather inaccessible, and extremely barren island belonging [[p. 295]] to the Spitsbergen group, and lying between North-East Land and Europe. It is about 250 miles from North Cape in Norway, and some 600 miles from the Kola Peninsula. On the island Mr. Koefoed saw four specimens of a large yellow and black Syrphus, walking about over the snow-free ground. One of these was collected, and is now in the possession of Mr. L. Natvig of the Oslo Museum, Norway. The position of Hope Island shows that these flies very likely formed part of the swarms that reached North-East Land on August 7th, and if this is so, they must have remained alive there for over a week.
The cause of these swarms of insects remains to be considered. In August 1869 Dunning (3) recorded "countless swarms of Syrphi" at Walton-on-the-Naze, on the Essex coast, and another observer noticed similar swarms at Margate on the same day. The Essex swarms consisted mainly of S. ribesii, S. corollae, and S. pyrastri. It is clear, then, that hover-flies are subject to occasional great increase in numbers. Now, I have shown (4) that the periodic abundance of mammals and birds in Northern Europe is mainly controlled by climatic factors acting at regular intervals. The explanation of the hover-fly swarms may be that good years cause unusual abundance of Aphids, upon which the hover-fly larvae feed. This idea is supported by the North-East Land episode, and also by the fact that ladybirds (Coccinella 7-punctata and bipunctata) were unusually abundant in Essex and Yorkshire in 1869, since ladybirds, like the hover-flies, feed on Aphids.
It may be noted that Amundsen, while on the north coast of Arctic America, noted (1) the arrival of gnats during a storm from the south-east. This would be a similar case to that of the North-East Land insects.
(b) Local migration of Fucomyia parvula against the wind.
On July 12th, 1924, examples of the seaweed-fly Fucomyia parvula Hal. were found in the shingle above high-tide mark, near the Expedition's Base Camp (south side of Reindeer Peninsula, Liefde Bay, North Spitsbergen). On this day none were flying, and they were hiding under the stones, and when exposed to light crawled at once very actively down into cracks among the stones, although the wings were expanded. The air temperature was about 10° C. in the shade, and the weather was cold and cloudy.
On July 23rd, i.e. eleven days later, numbers of these flies could be seen near the shore, flying quite fast against [[p. 296]] a light south wind. (One or two could also be seen being blown very fast in the opposite direction.) The sun was shining, and it felt quite hot, although the air temperature was only about 5° C. in the shade. The migration had no relation to the position of the flies' normal habitat (drifted seaweed).
Clearly the reactions of the flies to light had changed from positive to negative between July 12th and 23rd. A similar reversal of phototropism was noticed on board the expedition ship "Polarbjorn" in the case of the fly Leria modesta Mg. The larvae were living among herring refuse in the ship's hold, and began to pupate in large numbers in July. On, July 26th there were large numbers of newly emerged adults; hiding in the darkest corners, some with wings still unexpanded. On July 27th they were flying about outside in the sun. In the case of Fucomyia the reversal of phototropism was probably due to rise in insolation temperature, since in the arctic this is far more important than air temperature; in the case of Leria, to the changed physiological state of the flies. These examples illustrate how the reactions of insects may be reversed in nature by change in the animal or in the environment. Similar changes seem to occur on a much larger scale in locusts, causing them to migrate. It does not seem unreasonable to suggest that unusual climatic conditions in certain years may cause locusts to migrate in the same way that seasonal changes did in the Fucomyia, by reversing the normal tropisms.
(c) Local migration of blowflies.
Blowflies do not usually occur in Spitsbergen except near the coal settlements, and they have probably been brought there by ships. On July 3rd, 1924, numbers of blowflies (Phormia groenlandica Zett.) were found emerging from the carcase of a whale at Green Harbour, in Icefjord. On July 5th several examples were seen flying past at a distance of one to two miles from the whale, while dozens were to be seen flying round the carcase itself.
(d) Local migration of Chironomid flies.
On sunny days in the summer one usually sees a good many Chironomids flying along singly, and this habit of "voluntary migration" seems to be common to many species, e.g. Diamesa poultoni Edw., flying over snow-covered ground in early July 1921, on Prince Charles Foreland, and also at Green Harbour.
[[p. 297]] Quantities of driftwood are carried by the polar current over to Spitsbergen, from the north of Europe and Siberia. I have never succeeded in finding anything living in it, but it may occasionally act as a dispersal agent. Logs become frozen into the ice pack, and animals or their resting stages might thus be transported long distances without being in contact with salt water.
The same drift that carried the wood, carried the pack-ice from Siberia to Spitsbergen. Collembola might be carried on ice-floes, since some species, e.g. Agrenia bidenticulata, are in the habit of walking out over snowfields (probably in order to eat wind-blown pollen).
The sealing ships which visit Spitsbergen carry with them a small insect fauna. On the "Terningen" (1923) were a good many flies (Leria modesta Mg.). On the "Polarbjorn" (1924) were several species of flies (Leria, Limosina and blowflies), a beetle (Enicmus) and a spider (Leptyphantes leprosus Ohl.). The flies breed in the remains of herrings which are carried as cargo in the winter months to the Roman Catholic countries of southern Europe. The spider lives on the Limosina. It is thus apparent that the dispersal of insects to Spitsbergen is partly dependent on religious movements. So far, however, none of these species seem to have established themselves in Spitsbergen, except blowflies.
(a) The insects transported to Spitsbergen by birds include a flea (Ceratophyllus vagabundus Bohem.), occurring in the down of goose nests and possibly reintroduced every summer), and numerous mallophaga living on birds themselves.
(b) Birds may sometimes assist in the dispersal of free-living insects. On Bear Island during June 1921, kittiwake gulls could be seen carrying lumps of moss for some miles to their nesting cliffs. In their nests a good many flies and Collembola occur, which have obviously been brought there by the gulls in the moss.
(c) At Salmon Lake, Wijde Bay, North Spitsbergen, there is a colony of Arctic Terns, which nest on some of the small islands in the lake. On these islands in August 1924 there were enormous numbers of a mite, Bdella littoralis Linn. Now this mite normally occurs only at or [[p. 298]] below high-tide mark on the seashore, where it is very common. Here it was living on islands in a freshwater lake. Further, it occurred only on those islands where the terns were nesting, and not on the others. Since Arctic Terns often settle on, or nest on, shingle near the shore, where B. littoralis abounds, running about actively over the stones, it seems certain that the mites must have been accidentally carried to the islands by terns. This example illustrates the manner in which insects, e.g. Collembola, might also be dispersed by birds.
The concrete examples given above would make it appear that wind, flight, birds, and ships, are mainly responsible for the dispersal of the present fauna of insects to Spitsbergen. In the case of insects like flies, "voluntary migration" seems to play an important part, just as among butterflies and locusts.
1. The insect fauna of Spitsbergen is very scanty.
2. This scantiness is due to the high arctic character of the islands and to geographical isolation from Europe by sea.
3. The possible methods of dispersal of insects to Spitsbergen are: (1) Wind, or flight, or both, (2) Driftwood, (3) Drift-ice, (4) Ships, (5) Birds.
4. Examples of the action of some of these factors are given:--
(a) Syrphus ribesii and Dilachnus piceae and Tipulid fly, blown to North-East Land from Europe.
(b) Local "voluntary migration" of Fucomyia frigida, blowflies, and Chironomid flies.
(c) Fleas, mallophaga on birds.
(d) Gulls carrying insects in moss.
(e) Mites (Bdella littoralis) transported by Arctic Terns.
[[p. 299]] 5. REFERENCES.
1. AMUNDSEN, R. 1908. "The North-West Passage," vol. 2, p. 208: London.
2. COLLIN, J. E. 1923. "Diptera (Orthorrhapha Brachycera and Cyclorrhapha) from Spitsbergen and Bear Island," Ann. Mag. Nat. Hist., ser. 9, vol. 11, p. 116.
3. DUNNING, J. W. 1869. Proc. Ent. Soc. London, Nov. 15th, 1869, p. 25.
4. ELTON, C. S. 1924. "Periodic Fluctuations in the Numbers of Animals," Brit. J. Exp. Biol., vol. 2, p. 119.
5. HOEL, A. 1915. "D'ou vient le renne du Spitsberg?" Bull. Soc. Geogr. Paris, vol. 30, p. 443.
6. NANSEN, F. 1921. "Spitsbergen," p. 42: Leipzig.
7. SUMMERHAYES, V. S., and ELTON, C. S. 1923. "Contributions to the Ecology of Spitsbergen and Bear Island," J. Ecol., vol. 11, p. 214.