Chapter III: Causes of Variation (3)

[5] The great preponderance of the phytophagous over the predacious tribes, in the hotter regions of the earth, is a remarkable fact, and strongly suggestive of the relation which the insect and vegetable worlds (both of which attain their maximum in those zones) bear to each other. "The carnivorous beetles, or _Carabidae_," says Mr. Darwin, "appear in extremely few numbers within the tropics. The carrion-feeders and _Brachelytra_ are very uncommon; on the other hand, the _Rhynchophora_ and _Chrysomelidae_, all of which depend on the vegetable world for subsistence, are present in astonishing numbers. The orders _Orthoptera_ and _Hemiptera_ are peculiarly numerous; as is, likewise, the stinging division of the _Hymenoptera_, the bees, perhaps, being excepted."--Journal of Researches, p. 34.

[6] Mr. Westwood states that he possesses an individual of the _Papilio Machaon_ from the Himalayan Mountains, captured by Professor Royle, "which scarcely exhibits the slightest differences when compared with English specimens."--_The Butterflies of Great Britain_, p. 4.

[7] Zoologist, xiii. p. 4655.

[8] The Butterflies of Great Britain (London, 1855), p. 17.

[9] _Id._ p. 94.

[10] Insecta Maderensia (London, 1854), pp. 7, 8, 9.

[11] Insecta Maderensia, p. 516.

[12] Insecta Maderensia, p. 17.

[13] I possess specimens of this insect captured on the summit of Mount Olympus by my friend E. Armitage, Esq., who is also of opinion that it may be but a mountain state of the _C. sylvatica_, Linn.

[14] Introduction to the Modern Classification of Insects (London, 1840), ii. p. 473.

[15] Id. ii. p. 158.

[16] Introduction to the Modern Classification of Insects, ii. p. 431.

[17] Journal of Researches, p. 238.

[18] That I may not be misunderstood by those of my readers who conceive Madeira to be a kind of "arva beata," with the sky for ever blue, and (as a consequence) an unclouded sun; I would repeat, that I am not speaking of the vicinity of Funchal only (from which the invalids, who resort thither for their health, almost exclusively draw their deductions), but of _Madeira_,--and, more-over, of Madeira _as it was_, and not of Madeira as it is. More or less of cultivation during a period exceeding four centuries, in conjunction with the overwhelming fire which completely devastated the entire south of the island, immediately after its first settlers had taken possession of it, and which is stated (in the accounts which are transmitted to us) to have smouldered on for nearly seven years, have so altered the features of the country, that it is only in the untouched regions of the north (on which the woodman's axe is nevertheless encroaching, season after season, with lamentable rapidity) that we can catch even a glimpse of its pristine condition. The dense forests which then everywhere abounded must have caused an amount of moisture and exhalation of which even the northern districts as they now are (though saturated, even yet, with dampness; and at a certain elevation almost constantly enveloped with clouds) can give us but a faint idea. So tremendous indeed must have been the aqueous accumulations which then hung around the island, that even the splendour of a southern sun cannot have penetrated the atmosphere as it does at present; and, hence, the historical fact that Madeira proper (although separated by a channel of only thirty miles in breadth, and _now_ usually visible in bold relief against the sky, during a portion, at least, of every day, from a far greater distance) was not discovered for _an entire year_ after the colonization of Porto Santo, on account of the thickness of the canopy which shrouded it from view, is at once rendered intelligible. It is narrated, that, in the year 1419, Prince Henry of Portugal organized an expedition to attempt the doubling of Cape Bojador; but the commanders, having lost their reckoning, were driven ashore on an island,--which they named Porto _Santo_, in commemoration of their escape from the perils of the sea. "On their return," says Mr. Harcourt, "Prince Henry sent out Zargo, Vaz, and Pestrello, to plant a new colony in the island. It was not long before a dark spot was observed on the western horizon of Porto Santo. This was regarded by some with superstitious awe; but Zargo concluded it to be clouds attracted by high land; and shaping his course in that direction, in spite of the endeavours of his crew (by menaces and supplications) to prevent him, he discovered, in the year 1420, the island to which, from the trees that covered it, he gave the name of _Madeira_."--_A Sketch of Madeira_, London, 1851, p. 16.

[19] Journal of Researches, pp. 209, 210.

[20] Zoologist, x. 3616.

[21] Considering that I have already detected more than one thousand species in those islands, it may perhaps be questioned whether the same truth _is_ to be gathered from the result of my Madeiran researches. I would wish it therefore to be understood, first, that my statement refers to that group _as contrasted with countries in a similar latitude_; and, secondly, that its _real_ fauna is alone taken into account,--the host of introductions from more northern regions, a large proportion of which have probably taken place within a very recent period (as may be fairly presumed from the knowledge that fresh arrivals, an almost necessary consequence of the importation of plants, _are_ occurring nearly every season), having been dismissed from our present inquiry.

[22] I perceive, on reference to the original examples, still in my collection, that this was wrongly quoted as the _Haltica rufipes_. It is the _H. exoleta_, Fabr., and it is thus entered in Messrs. Hardy and Bold's 'Catalogue of the Insects of Northumberland and Durham;' where they make the observation, "variable in colour; specimens from the sea-coast are frequently of a dark mahogany tint." I have myself indeed, since I communicated the above remarks to the 'Zoologist,' taken its precise counterpart, in abundance, along the Yorkshire coast,--from Bridlington to the extremity of Flamborough Head; so that it may perhaps be regarded as a topographical state which is more especially peculiar to the eastern shores of England, north of the Humber.

[23] Zoologist, iv. pp. 1283, 1284.

[24] Geodephaga Britannica (London, 1854), p. 186.

[25] Zoologist, iii. p. 900.

[26] Zoologist, v. p. 1941.

[27] Monographie des _Anthicus_ (Paris, 1848), p. 149.

[28] _Id._ pp. 127, 128.

[29] Proceedings of the Entomological Society of London (Part 3. New Series), p. 4.

[30] Insecta Maderensia, pp. 55, 56.

[31] Trans. of the Ent. Soc. of London, ii. pp. 59, 62.

[32] Considering that the true _Vanessa Atalanta_, of more northern latitudes, _does_ occasionally occur around Funchal, it may be reasonably contended that the fact of its coexistence (on the same spot) with the _V. Callirhoe_ is strong presumptive proof that the latter is a true species, and no climatal or insular modification of the former. And so, judging from a distance, and without local evidence to explain this phaenomenon, I should have concluded myself: nevertheless, recollecting how easy of transport the larvae and pupae of Lepidoptera necessarily are (of which we have the plainest assurance in the almost certain introduction of the _Pontia Brassicae_, _Sphinx Convolvuli_, _Acherontia Atropos_, &c. into those islands), especially in a region which for more than a century has been receiving a constant supply of vegetables and ornamental plants from western Europe; I am induced to believe that the appearance of the _Atalanta_ is a comparatively recent one, whilst that of the _Callirhoe_ (which, unlike the typical _Red Admiral_, has naturalized itself in nearly all portions of the group) must be referred to the remote period when migrations over a long-lost continuous land were in regular operation. The _slowness_ of the change, in external aspect, which the isolation of insects from geological causes would seem to bring about (and which follows, as a corollary, if the above conclusion be true), I propose to discuss in a subsequent chapter of this work.

[33] Insecta Maderensia, p. 260.

[34] Insecta Maderensia, pp. 268, 269.

[35] Religion of Nature Delineated, p. 99.

[36] Although the result of a primary (or creative) adjustment to special circumstances, rather than of a secondary adaptation, brought about by a self-modifying capability; we may just call attention to the fact, that most of the blind insects, whether associates within the nests of ants, or natives of subterranean caverns, have either their palpi _or_ antennae anomalously developed,--as though, partially (although how, and in what degree, we cannot possibly ascertain), to make amends for the inconvenience which a total want of sight must, necessarily entail.

[37] This is certainly rendered _probable_, however, from the fact that a large proportion of these apterous species are members of _genera_ which are usually winged,--such as _Tarus_, _Loricera_, _Calathus_, _Olisthopus_, _Argutor_, _Trechus_, _Hydrobius_, _Ephistemus_, _Syncalypta_, _Phloe ophagus_, _Tychius_, _Longitarsus_, _Chrysomela_, _Scymnus_, _Corylophus_, _Helops_, and _Othius_,--whilst the knowledge that, out of twenty-nine genera which I believe to be endemic in those islands, six only are winged (the remaining twenty-three being apterous), will not tend to diminish the probability that there is something peculiar in the action of Madeiran influences generally on the alary system of the insect tribes.

[38] I do not think it necessary to apologize for the apparent disposal of this _quaestio vexata_; because, from the wildness of the upland ridges to which the _D. obscuroguttatus_ is in Madeira exclusively confined, I deem it an absolute impossibility that it could ever have been _introduced_, through any chance agencies whatsoever. And hence, unless we reject the doctrine of specific centres _in toto_, I contend that it must have migrated, together with other insects similarly circumstanced, by ordinary means, and without natural impediments, from its own area of diffusion.

[39] I am informed by Dr. Hooker, that the only two insects (belonging respectively to the orders Coleoptera and Lepidoptera) which he detected in Kerguelen's Land were wingless.

[40] Insecta Maderensia, p. 6.

[41] Insecta Maderensia, p. 36.

[42] _Id._ p. 310.

[43] Insecta Maderensia, p. 452.

[44] Insecta Maderensia, p. 11.

[45] Religion of Nature Delineated, p. 84.