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Island Life; Or, The Phenomena and Causes of Insular Faunas and Floras
For the Lepidoptera I first noted all the species and varieties marked as British only in Staudinger's Catalogue of European Lepidoptera. This list was carefully corrected by Mr. Stainton, who weeded out all the species known by him to have been since discovered, and furnished me with valuable information on the distribution and habits of the species. This information often has a direct bearing on the probability of the insect being peculiar to Britain, and in some cases may be said to explain why it should be so. For example, the larvæ of some of our peculiar species of Tineina feed during the winter, which they are enabled to do owing to our mild and insular climate, but which the severer continental winters render impossible. A curious example of the effect this habit may have on distribution is afforded by one of our commonest British species, Elachista rufocinerea, the larva of which mines in the leaves of Holcus mollis and other grasses from December to March. This species, though common everywhere with us, extending to Scotland and Ireland, is quite unknown in similar latitudes on the continent, but appears again in Italy, the South of France, and Dalmatia, where the mild winters enable it to live in its accustomed manner.
Such cases as this afford an excellent illustration of those changes of distribution, dependent probably on recent changes of climate, which may have led to the restriction of certain species to our islands. For should any change of climate lead to the extinction of the species in South Europe, where it is far less abundant than with us, we should have a common and wide-spread species entirely restricted to our islands. Other species feed in the larva state on our common gorse, a plant found only in limited portions of Western and Southern Europe; and the presence of this plant in a mild and insular climate such as ours may well be supposed to have led to the preservation of some of the numerous species which are or have been dependent on it. Since the first edition was published many new British species have been discovered, while some of the supposed peculiar species have been found on the continent. Information as to these has been kindly furnished by Mr. W. Warren, Mr. C. G. Barrett, Lord Walsingham, and other students of British Lepidoptera, and the first-named gentleman has also looked over the proofs.
Mr. McLachlan has kindly furnished me with some valuable information on certain species of Trichoptera or Caddis flies which seem to be peculiar to our islands; and this completes the list of orders which have been studied with sufficient care to afford materials for such a comparison. We will now give the list of peculiar British Insects, beginning with the Lepidoptera and adding such notes as have been supplied by the gentlemen already referred to.
List of the Species or Varieties of Lepidoptera which, so far as at present known, are confined to the British Islands. (The figures show the dates when the species was first described. Species added since the first edition are marked with an asterisk.)
Diurni1. Polyommatus dispar. "The large copper." This fine insect, once common in the fens, but now extinct owing to extensive drainage, is generally admitted to be peculiar to our island, at all events as a variety or local form. Its continental ally differs constantly in being smaller and in having smaller spots; but the difference, though constant, is so slight that it is now classed as a variety under the name of rutilus. Our insect may therefore be stated to be a well-marked local form of a continental species.
2. Lycæna astrarche, var. artaxerxes. This very distinct form is confined to Scotland and the north of England. The species of which it is considered a variety (more generally known to English entomologists as P. agestis) is found in the southern half of England, and almost everywhere on the continent.
Bombyces3. Lithosia complana, var. sericea. North of England (1861).
4. Hepialus humuli, var. hethlandica. Shetland Islands (1865). A remarkable form, in which the male is usually yellow and buff instead of pure white, as in the common form, but exceedingly variable in tint and markings.
5. Epichnopteryx reticella. Sheerness, Gravesend, and other localities along the Thames (1847); Hayling Island, Sussex.
6. E. pulla, var. radiella. Near London, rare (1830?); the species in Central and Southern Europe. (Doubtfully peculiar in Mr. Stainton's opinion.)
Noctuæ7. Acronycta euphorbiæ, var. myricæ. Scotland only (1852). A melanic form of a continental species.
8. Agrotis subrosea. Cambridgeshire and Huntingdonshire fens, perhaps extinct (1835). The var. subcærulea is found in Finland and Livonia.
9. Agrotis candelarum var. ashworthii. South and West (1855). Distinct and not uncommon.
10. Luperina luteago, var. barretti. Ireland (1864).
11. Aporophyla australis, var. pascuea. South of England (1830). A variety of a species otherwise confined to South Europe.
12. Hydræcia nictitans, var. paludris.
Geometræ13. Boarmia gemmaria, var. perfumaria. Near London and elsewhere. A large dark variety of a common species.
14. *B. repandata, var. sodorensium. Outer Hebrides.
15. *Emmelesia albulata, var. hebridium. Outer Hebrides.
16. *E. albulata, var. thules. Shetland Islands.
17. *Melanippe montanata, var. shetlandica. Shetland Islands.
18. *M. sociata, var. obscurata. Outer Hebrides. A dark form.
19. Cidaria albulata, var. griseata. East of England (1835). A variety of a species otherwise confined to Central and Southern Europe.
20. Eupithecia constrictata.. Widely spread, but local (1835). Larva on thyme.
21. *E. satyrata, var. curzoni. N. Scotland.
22. *E. nanata var. curzoni. Shetland Islands.
Pyralidina23. Aglossa pinguinalis, var. streatfieldi. Mendip Hills (1830). A remarkable variety of the common "tabby."
24. *Scoparia cembræ, var. scotica. Scotland (1872).
25. *Myelois ceratoniæ, var. pryerella. North London (1871).
26. *Howœosoma nimbella, var. saxicola. England, Scotland, Isle of Man (1871).
27. *Epischnia bankesiella. Isle of Portland (1888).
Tortricina28. Aphelia nigrovittana. Scotland (1852). A local form of the generally distributed A. lanceolana.
29. Grapholita parvulana. Isle of Wight (1858). Rare. A distinct species.
30. Conchylis erigerana. South-east of England (1866).
31. *Brachytænia woodiana. Herefordshire (1882).
32. *Eupœcilia angustana, var. thuleana. Shetland Islands.
33. *Tortrix donelana. Connemara, Ireland (1890).
Tineina34. Tinea cochylidella. Sanderstead, near Croydon (1854). Unique!
35. Acrolepia betulætella. Yorkshire and Durham (1840). Rare.
36. Argyresthia semifusca. North and West of England (1829). Rather scarce. A distinct species.
37. Gelechia divisella. A fen insect (1856). Rare.
38. G. celerella. West of England (1854). A doubtful species.
39. *G. tetragonella. Yorkshire. Norfolk. Salt marshes.
40. *G. sparsiciliella. Pembroke.
41. *G. plantaginella. A salt-marsh species.
42. G. Ocellatella (Barrett nec Stainton). Bred from Beta maritima. Very distinct.
43. Bryotropha politella. Moors of North of England. Norfolk (1854).
44. *B. portlandicella. Isle of Portland (1890).
45. Lita fraternella. Widely scattered (1834). Larva feeds on shoots of Stellaria uliginosa in spring.
46. L. blandulella. Kent.
47. Anacampsis sircomella. North and West England (1854). Perhaps a melanic variety of the more widely spread A. tæniolella.
48. A. immaculatella. West Wickham (1834). Unique! A distinct species.
49. *Œcophora woodiella?
50. Glyphipteryx cladiella. Eastern Counties (1859). Abundant.
51. G. schœnicolella. In several localities (1859).
52. Gracilaria stramineella. (1850). On birch. Perhaps a local form of G. elongella, found on alder.
53. Ornix loganella. Scotland (1848). Abundant, and a distinct species.
54. O. devoniella. In Devonshire (1854). Unique!
55. Coleophora saturatella. South of England (1850). Abundant on broom.
56. C. inflatæ. South and East of England. On Silene inflata. ? continental.
57. C. squamosella. Surrey (1856). Very rare, but an obscure species.
58. C. salinella. On Sea-coast (1859). Abundant.
59. *C. potentillæ. South of England.
60. *C. adjunctella. Essex salt marshes. ? Lancashire (1882).
61. *C. limoniella. Isle of Wight. Feeds on Statice limonium.
62. Elachista flavicomella. Dublin (1856). Excessively rare, two specimens only known.
63. *E. scirpi. Wales and Sussex. Salt marshes.
64. E. consortella. Scotland (1854). A doubtful species.
65. E. megerlella. Widely distributed (1854). Common. Larva feeds in grass during winter and early spring.
66. E. obliquella. Near London (1854). Unique!
67. E. triseriatella. South of England (1854). Very local; an obscure species.
68. *Tinagma betulæ. East Dorset (1891).
69. Lithocolletis nigrescentella. Northumberland (1850). Rare; a dark form of L. Bremiella, which is widely distributed.
70. *L. anderidæ. Sussex. Dorset (1886).
71. L. irradiella. North Britain (1854). A northern form of the more southern and wide-spread L. lautella.
72. L. triguttella. Sanderstead, near Croydon (1848). Unique! very peculiar.
73. L. ulicicolella. In a few wide-spread localities (1854). A peculiar form.
74. L. caledoniella. North Britain (1854). A local variety of the more widespread L. corylifoliella.
75. L. dunningiella. North of England (1852). A somewhat doubtful species.
76. Bucculatrix demaryella. Widely distributed (1848). Rather common.
77. Trifurcula squamatella. South of England (1854). A doubtful species.
78. Nepticula ignobiliella. Widely scattered (1854). On hawthorn, not common. ? on continent.
79. N. poterii. South of England (1858). Bred from Larvæ in Poterium sanguisorba.
80. N. quinquella. South of England (1848). On oak leaves, very local. ? continental.
81. N. apicella. Local (1854). Probably confused with allied species on the continent.
82. N. headleyella. Local (1854). A rare species.
83. *N. hodgkinsoni. Lancashire.
84. *N. woolhopiella. Herefordshire.
85. *N. serella. Westmoreland and S. England.
86. *N. auromarginella. Dorset (1890).
87. *Micropteryx sangii. (1891).
88. *M. salopiella.
Pterophorina89. Agdistis bennetti. East coast. I. of Wight (1840). Common on Statice limonium.
We have here a list of eighty-nine species, which, according to the best authorities, are, in the present state of our knowledge, peculiar to Britain. It is a curious fact that no less than fifty of these have been described more than twenty-five years; and as during all that time they have not been recognised on the continent, notwithstanding that good coloured figures exist of almost all of them, it seems highly probable that many of them are really confined to our island. At the same time we must not apply this argument too rigidly, for the very day before my visit to Mr. Stainton he had received a letter from Professor Zeller announcing the discovery on the continent of a species of our last family, Pterophorina, which for more than forty years had been considered to be exclusively British. This insect, Platyptilia similidactyla (Pterophorus isodactylus, Stainton's Manual), had been taken rarely in the extreme north and south of our islands—Teignmouth and Orkney, a fact which seemed somewhat indicative of its being a straggler. Again, seven of the species are unique, that is, have only been captured once; and it may be supposed that, as they are so rare as to have been found only once in England, they may be all equally rare and not yet found on the continent. But this is hardly in accordance with the laws of distribution. Widely scattered species are generally abundant in some localities; while, when a species is on the point of extinction, it must for a time be very rare in the single locality where it last maintains itself. It is then more probable that some of these unique species represent such as are almost extinct, than that they have a wide range and are equally rare everywhere; and the peculiarity of our insular climate, combined with our varied soil and vegetation, offer conditions which may favour the survival of some species with us after they have become extinct on the continent.
Of the sixty-nine species recorded in my first edition fourteen have been since discovered on the continent, while no less than twenty-two species and eleven varieties have been added to the list. As we can hardly suppose continental entomologists to be less thorough collectors than ourselves, it ought to be more and more difficult to find any insects which are unknown on the continent if all ours really exist there; and the fact that the list of apparently peculiar British species is an increasing one renders it probable that many of them are not only apparently but really so. Both general considerations dependent on the known laws of distribution, and the peculiar habits, conspicuous appearance, and restricted range, of many of our species, alike indicate that some considerable proportion of them will remain permanently as peculiar British species.
We will now pass on to the Coleoptera, or beetles, an order which has been of late years energetically collected and carefully studied by British entomologists.
List of the Species and Varieties of Beetles which, so far as at present known, are confined to the British Islands. Those added since the first edition are marked with an asterisk.
Carabidæ1. *Bembidium saxatile, var. vectensis (Fowler). Isle of Wight.
2. Dromius vectensis (Rye). Common in the Isle of Wight, also in Kent, and at Weymouth and Seaton. Closely allied to D. sigma.
3. Harpalus latus, var. metallescens (Rye). Unique, but very marked! South coast. "Perhaps a sport or a hybrid" (Fowler).
4. Acupalpus derelictus (Dawson). Unique! North Kent. Canon Fowler thinks it may be a variety of A. dorsalis.
Dyticidæ5. *Acilius sulcatus, var. scoticus (Curtis). Scotland. A melanic variety.
Helophoridæ6. Ochthebius poweri (Rye). Very marked. S. coast. A few specimens only.
7. *O. æneus (Steph).
Brachyelytra8. Ocyusa hibernica (Rye). Ireland, mountain tops, and at Braemar.
9. *Oxypoda tarda (Sharp).
10. ,, pectita (Sharp). Scotland.
11. ,, verecunda (Sharp). Scotland, also London districts.
12. Homalota diversa (Sharp).
13. ,, fulvipennis (Rye).
14. ,, oblongiuscula (Sharp). Scotland, also England and Ireland.
15. ,, princeps (Sharp). A coast insect.
16. ,, curtipennis (Sharp). Scotland and near Birmingham.
17. H. levana, var. setigera (Sharp).
18. Stenus oscillator (Rye). Unique! South coast. May be a hybrid.
19. Trogophlæus spinicollis (Rye). Mersey estuary, unique! Most distinguishable, nothing like it in Europe. Perhaps imported from another continent.
20. Eudectus whitei (Sharp). Scotch hills. A variety of E. Giraudi of Germany (the only European species) fide Kraatz (Sharp).
21. Homalium rugulipenne (Rye). Exceedingly marked form. Northern and western coasts; rare.
22. *Mycetoporus monticola (Fowler). Cheviots and Inverness-shire.
Scydmænidæ23. *Scydmænus poweri (Fowler) S. England. A recent discovery.
24. *S. planifrons (Fowler). ,, ,,
Pselaphidæ25. Bryaxis cotus (De Sauley). Scotland.
26. Bythinus glabratus (Rye). Sussex coast; also Isle of Wight; a few specimens; very distinguishable; myrmecophilous (lives in ants' nests).
Trichopterygidæ27. Ptinella maria (Matthews) Derbyshire.
28. Trichopteryx saræ ( ,, ) Notts.
29. ,, poweri ( ,, ) Oxon.
30. ,, edithia ( ,, ) Kent.
31. ,, *angusta ( ,, ) Leicestershire.
32. ,, kirbii ( ,, ) Norfolk.
33. ,, fratercula ( ,, )
34. ,, waterhousii ( ,, )
35. ,, championis ( ,, ) Wicken Fen.
36. ,, jansoni ( ,, ) Leicestershire.
37. ,, suffocata (Haliday). Ireland, Co. Cork.
38. ,, carbonaria (Matthews). Notts.
39. Ptilium halidayi (Matthews). Sherwood Forest.
40. ,, caledonicum (Sharp). Scotland; very marked form.
41. ,, insigne (Matthews). London district.
42. *Orthoperus mundus (Matthews). Oxfordshire.
43. *O. punctulatus (Matthews). Lincolnshire.
Anisotomidæ44. Agathidium rhinoceros (Sharp). Old fir-woods in Perthshire; local, many specimens; a very marked species.
45. Anisotoma similata (Rye). South of England. Two specimens.
46. ,, lunicollis (Rye). North-east and South of England, a very marked form; several specimens.
Phalacridæ47. Phalacrus brisouti (Rye). South of England. Rare. "Perhaps a small form of P. coruscus" (Fowler).
Cryptophagidæ48. Atomaria divisa (Rye). Unique! South of England.
Lathridiidæ49. Melanopthalma transversalis, var. wollastoni (Waterhouse). South coast, and Lincolnshire.
Byrrhidæ50. Syncalypta hirsuta (Sharp). South of England, local. "Closely allied to S. setigera" (Fowler).
Mordellidæ51. *Anaspis septentrionalis. Scotland (1891). (Champion.)
52. * ,, garneysi (Fowler). London District. (1890.)
Telephoridæ53. Telephorus darwinianus (Sharp). Scotland, sea-coast. A stunted form of abnormal habits. Perhaps a variety of T. lituratus.
Cyphonidæ54. Cyphon punctipennis (Sharp). Scotland.
Anthicidæ55. Anthicus salinus (Crotch). South coast.
56. ,, scoticus (Rye). Loch Leven; very distinct; many specimens.
Cioidæ57. *Cis bilamellatus (Wood). West Wickham, Kent. "Perhaps imported. Has the appearance of an exotic Cis" (Fowler).
Tomicidæ58. *Pityopthorus lichtensteinii, var. scoticus (Blandford). Scotland.
Curculionidæ59. Ceuthorhynchus contractus, var. pallipes (Crotch). Lundy Island; several specimens. A curious variety only known from this island.
60. Liosomus troglodytes (Rye). A very queer form. Two or three specimens. South of England.
61. *Orcheites ilicis, var. nigripes (Fowler). London District. (1890.)
62. Apion ryei (Blackburn). Shetland Islands. Several specimens. Perhaps a var. of A. fagi.
Chrysomelidæ63. Chrysomela staphylea, var. sharpi (Fowler). Solway district.
Halticidæ64. Longitarsus agilis (Rye). South of England; many specimens.
65. ,, distinguenda (Rye). South of England; many specimens.
66. Psylliodes luridipennis (Kutschera). Lundy Island. A very curious form, not uncommon in this small island, to which it appears to be confined. "An extreme and local variety of P. chrysocephala" (Fowler).
Coccinellidæ67. Scymnus lividus (Bold). Northumberland. A doubtful species.
Of the sixty-seven species and varieties of beetles in the preceding list, a considerable number no doubt owe their presence there to the fact that they have not yet been discovered or recognised on the continent. This is almost certainly the case with many of those which have been separated from other species by very minute and obscure characters, and especially with the excessively minute Trichopterygidæ described by Mr. Matthews. There are others, however, to which this mode of getting rid of them will not apply, as they are so marked as to be at once recognised by any competent entomologist, and often so plentiful that they can be easily obtained when searched for. The peculiar species of Apion in the Shetland Islands is interesting, and may be connected with the very peculiar climatal conditions there prevailing, which have led in some cases to a change of habits, so that a species of weevil (Otiorhynchus maurus) always found on mountain sides in Scotland here occurs on the sea-shore. Still more curious is the occurrence of two distinct forms (a species and a well-marked variety) on the small granitic Lundy Island in the Bristol Channel. This island is about three miles long and twelve from the coast of Devonshire, consisting mainly of granite with a little of the Devonian formation, and the presence here of peculiar insects can only be due to isolation with special conditions, and immunity from enemies or competing forms. When we consider the similar islands off the coast of Scotland and Ireland, with the Isle of Man and the Scilly Islands, none of which have been yet thoroughly explored for beetles, it is probable that many similar examples of peculiar isolated forms remain to be discovered.
Looking, then, at what seem to me the probabilities of the case from the standpoint of evolution and natural selection, and giving due weight to the facts of local distribution as they are actually presented to us, I am forced to differ from the opinion held by our best entomological authorities, and to believe that some at least, perhaps many, of the species which, in the present state of our knowledge, appear to be peculiar to our islands, are, not only apparently, but really, so peculiar.
I am indebted to Mr. Robert McLachlan for the following information on certain Trichopterous Neuroptera (or caddis-flies) which appear to be confined to our islands. The peculiar aquatic habits of the larvæ of these insects, some living in ponds or rivers, others in lakes, and others again only in clear mountain streams, render it not improbable that some of them should have become isolated and preserved in our islands, or that they should be modified owing to such isolation.
Trichoptera peculiar to the British Isles1. Philopotamus insularis. (? A variety of P. montanus.)—This can hardly be termed a British species or variety, because, so far as at present known, it is peculiar to the Island of Guernsey. It agrees structurally with P. montanus, a species found both in Britain and on the continent, but it differs in its strikingly yellow colour, and less pronounced markings. All the specimens from Guernsey are alike, and resident entomologists assured Mr. McLachlan that no other kind is known. Strange to say, some examples from Jersey differ considerably, resembling the common European and British form. Even should this peculiar variety be at some future time found on the continent it would still be a remarkable fact that the form of insect inhabiting two small islands only twenty miles apart should constantly differ; but as Jersey is between Guernsey and the coast, it seems just possible that the more insular conditions, and perhaps some peculiarity of the soil and water in the former island, have really led to the production or preservation of a well-marked variety of insect. In the first edition of this work two other species were named as then, peculiar to Britain—Setodes argentipunctella and Rhyacophila munda, but both have now been taken on the continent.
2. Mesophylax impunctatus, var. zetlandicus.—A variety of a South and Central European species, one specimen of which has been found in Dumfriesshire. The variety is distinguished by its small size and dark colour.
Land and Freshwater Shells.—In the first edition of this work four species were noted as being, so far as was then known, exclusively British. Two of these, Cyclas pisidioides (now called Sphærium pisidioides) and Geomalacus maculosus, have been discovered on the continent, but the other two remain still apparently confined to these islands; and to these another has been added by the discovery of a new species of Hydrobia in the estuary of the Thames. The peculiar species now stands as follows:—
