LETTER XLIX.

_GEOGRAPHICAL DISTRIBUTION OF INSECTS; THEIR STATIONS AND HAUNTS; SEASONS; TIMES OF ACTION AND REPOSE._

Though no subject is more worthy of the attention of the Entomologist than the _Geographical Distribution_ of insects, yet perhaps there is none connected with the science, for the elucidation of which he is furnished with fewer materials. The geographer of these animals sitting by his fireside, even supposing his museum as amply stored as that of Mr. MacLeay, and the _habitats_ of its contents as accurately indicated, still labours under difficulties that are almost insuperable; so that it is next to impossible, with our present knowledge of the subject, to give _satisfactory_ information upon _every_ point which it includes. Had he the talents and opportunities of a Humboldt, and could, like him, traverse a large portion of the globe, he would endeavour to note the elevation, the soil and aspect, the latitude and longitude, the mean temperature and meteorological phænomena, the season of the year, the kind of country, and other localities connected with the insects he captured, and so might build his superstructure upon a sure basis. But these are things seldom registered by travellers that take the trouble to collect insects; who, if they specify generally the country in which any individual was found, think they have done enough. But to say that an insect was taken in India, China, New Holland, and North or South America,--when we consider the vast extent of those regions,--is saying little of what one wishes to know even with respect to its _habitat_. You must regard therefore, after all, what I have been able to collect,--and for which I am greatly indebted to the labours of my few but able precursors in this walk,--as merely approximations to an _outline_, rather than as a correct _map_ of insect Geography.

Amongst the numerous obligations that he conferred upon Natural History, Linné was the first Naturalist who turned his attention to the _Geographical Distribution_ of its objects, especially that of the _Vegetable_ Kingdom[1458]: and the accomplished traveller Baron Humboldt, by the observations he made on this subject in the course of his peregrinations in tropical America, has furnished the Botanist with a clue which, duly followed, will enable him to perfect that part of his science; an end to which the learned observations of Messrs. R. Brown and Decandolle have greatly contributed[1459]. With regard to _animals_, Mr. White, so long ago as 1773, had observed that they, as well as plants, might with propriety be arranged geographically[1460]: and in 1778 Fabricius in his _Philosophia Entomologica_ applied the principle to _insects_[1461]. Nearly forty years elapsed before any improvement or enlargement of this last department was attempted; when in 1815 M. Latreille, stimulated by what had been effected in Botany, in a learned and admirable memoir[1462] endeavoured to place Entomology in this respect by the side of her more fortunate sister: and subsequently Mr. W. S. MacLeay, in the memorable work so often quoted in our correspondence, has viewed the subject in another light, and added some important information to what had been before collected[1463].

The point now under consideration naturally divides itself into two principal branches;--the _numerical_ distribution of insects, and the _topographical_.

I. By the _numerical_ distribution of insects I mean not only the number which PROVIDENCE has employed to carry on its great plan on this terraqueous globe, or any given portion of it; or of the species of which each group or genus may be supposed to consist; or of the comparative number of individuals furnished by each species,--points of no easy solution: but more particularly their distribution according to their _functions_, whether they prey upon _animal_ or _vegetable_ matter, and in its _living_ or _decaying_ state.

We have no data enabling us to ascertain with any degree of accuracy the actual _number_ of species of insects and _Arachnida_ distributed over the surface of the globe; but it is doubtless regulated in a great degree by that of plants. We should first then endeavour to gain some just though general notion on that head. Now Decandolle conjectures that the number of the species of plants, 60,000 being already known, may be somewhere between 110,000 and 120,000[1464]. If we consider with reference to this calculation, that though the great body of the mosses, lichens, and sea-weeds are exempt from the attack of insects, yet as a vast number of phanerogamous plants and fungi are inhabited by _several_ species, we may form some idea how immense must be the number of existing insects; and how beggarly does Ray's conjecture of 20,000 species[1465], which in his time was reckoned a magnificent idea, appear in comparison! Perhaps we may obtain some approximation by comparing the number of the species of insects already discovered in _Britain_ with that of its _phanerogamous_ plants. The latter,--and it is not to be expected that any large number of species have escaped the researches of our numerous Botanists,--may be stated in round numbers at 1500, while the British insects, (and _thousands_ it is probable remain still undiscovered,) amount to 10,000; which is more than _six_ insects to _one_ plant. Now though this proportion, it is probable, does not hold universally; yet if it be considered how much more prolific in species tropical regions are than our chilly climate, it may perhaps be regarded as not very wide of a fair medium. If then we reckon the phanerogamous vegetables of the globe in round numbers at 100,000 species, the number of insects would amount to 600,000. If we say 400,000, we shall perhaps not be very wide of the truth. When we reflect how much greater attention has been paid to the collection of plants than to that of insects, and that 100,000 species of the latter may be supposed already to have a place in our cabinets[1466], we may very reasonably infer that at least _three fourths_ of the existing species remain undiscovered.

Certain groups and genera are found to contain many more species than others: for instance, the _Coleoptera_ and _Lepidoptera_ Orders than the _Orthoptera_ and _Neuroptera_; the _Rhincophora_ than the _Xylophagi_: the _Dytiscidæ_ than the _Gyrinidæ_; _Aphodius_ than _Geotrupes_; _Carabus_ than _Calosoma_. Again, some insects are much more prolific than others. Thus the _Diptera_ Order, though not half so numerous with respect to _species_ as the _Coleoptera_, exceeds it greatly in the number of _individuals_, filling the air in every place and almost at every season with its dancing myriads. We rarely meet with a single individual of the most common species of _Calosoma_ or _Buprestis_; whilst the formicary, the termitary, the vespiary, and the bee-hive send forth their thousands and tens of thousands; and whole countries are covered and devastated by the _Aphides_ and the Locusts. An all-wise PROVIDENCE has proportioned the numbers of each group and species to the work assigned to them. And this is the view in which the numerical distribution of insects is most interesting and important: and we are indebted to Mr. W. S. MacLeay for calling the attention of Entomologists more particularly to this part of our present subject.

With regard to their _functions_, insects may be primarily divided into those that feed upon _animal_ matter and those that feed upon _vegetable_. At first you would be inclined to suppose that the _latter_ must greatly exceed the _former_ in number: but when you reflect that not only a very large proportion of Vertebrate animals, and even some _Mollusca_[1467], have more than _one_ species that preys upon them, but that probably the majority of insects, particularly the almost innumerable species of _Lepidoptera_, are infested by parasites of their own class, sometimes having a different one appropriated to them in each of their preparatory states[1468], and moreover that a large number of beetles and other insects devour both living and dead animals,--you will begin to suspect that these two tribes may be more near a counterpoise than at first seemed probable. In fact, out of a list of more than 8000 British insects and _Arachnida_ taken several years ago, and furnished chiefly by Mr. Stephens, I found that 3894 might be called carnivorous, and 3724 phytiphagous[1469]; so that, speaking roundly, they might be denominated equiponderant.

Carnivorous and phytiphagous insects may be further subdivided according to the _state_ in which they take their _food_,--whether they attack it while _living_, or not till after it is _dead_. To adopt Mr. W. S. MacLeay's phraseology, the former may be denominated _thalerophagous_, and the latter _saprophagous_. The British saprophagous _carnivorous_ insects, compared with those that are thalerophagous, are about as 1:6; while the phytiphagous ones are as 1:9. The _thalerophaga_ in both tribes may be further subdivided as they take their food by _suction_ or _mastication_: in the _carnivorous_ ones, the suckers to the masticators in Britain are nearly as 1:6; but with respect to the _phytiphagous_ tribe you must take into consideration that some insects imbibing their food by _suction_ in their _perfect_ state (as the great body of the _Lepidoptera_), _masticate_ it when they are _larvæ_: deducting therefore from both sides the insects thus circumstanced, the masticators will form about _three fourths_ of the remaining British thalerophagous insects. Another circumstance belonging to this head must not be passed without notice:--there are certain insects feeding upon liquid food that do not _suck_, but _lap_ it. This is the case with the _Hymenoptera_, who, though they are mandibulate, generally lap their food (the nectar of flowers) with their tongue, and may be called _lambent_ insects: nor is this practice confined to that order, but all the mandibulate insects that feed on that substance merit the same appellation. The absorption of this nectar is so important a point in the economy of nature, that a very large proportion of the insect population of the globe in their perfect state, are devoted to it. Considerably more than half the species indigenous to Britain fulfill this function, and probably in tropical countries the proportion may be still larger.

To push this analysis still further--Amongst our carnivorous thalerophaga, _aphidivorous_ insects are about as 1:14; and amongst the phytiphagous, the _fungivorous_ ones form about a _twentieth_; and the _granivorous_ about a _twenty-fifth_ part of the whole. Again: in the _saprophaga_ the _lignivorous_ tribes form more than _half_, and the _coprophagous_ ones more than a _third_.

If you wish to know further the relative proportions of the different _Orders_ to each other--The _Coleoptera_ may be stated as forming at least 1:2 of our intire insect population; the _Orthoptera_ and _Dermaptera_ as about 1:160; the _Hemiptera_ as 1:15; the _Lepidoptera_ as more than 1:4; the _Neuroptera_ with the _Trichoptera_ as 1:29; the _Hymenoptera_ as about 1:4; the _Diptera_ as not 1:7; and the _Aptera_ and _Arachnida_ as perhaps amounting to 1:19[1470].

To extend this inquiry to _exotic_ and more particularly to _extra-European_ insects, in the present state of our knowledge, would lead to no very satisfactory results. The lists we have are so imperfect, that those which tell most in this country,--I mean the more minute insects and the _Brachyptera_--have hitherto formed a very small, if any part, of the collections made _out_ of Europe. Mr. W. S. MacLeay however, who, besides his father's (particularly rich in _Petalocera_), has had an opportunity of examining the Parisian and other cabinets, finds that the species of _coprophagous_ insects _within_ the tropics, to those _without_, are nearly in the proportion of 4:3; and that the coprophagous _Petalocera_, to the remainder of the saprophagous ones, may be represented by 3:2[1471]. It may be inferred, from the superabundance of plants and animals in equinoctial countries, that the number of species of insects in general is greater within than without the tropics: the additional momentum produced by the vast size of many of the tropical species must also be taken into consideration.

II. There are three principal points that call for attention under the _second_ branch of our present subject--the _topographical_ distribution of insects; namely, their _Climates_, their _Range_, and their _Representation_.

i. Entomologists, taking _heat_ for the principal regulator of the station of insects, have divided the globe into entomological _climates_. Fabricius considers it as divisible into _eight_ such climates, which he denominates the _Indian_, _Egyptian_, _Southern_, _Mediterranean_, _Northern_, _Oriental_, _Occidental_, and _Alpine_. The first containing the tropics; the second, the northern region immediately adjacent; the third, the southern; the fourth, the countries bordering on the Mediterranean sea, including also _Armenia_ and _Media_; the fifth, the northern part of Europe interjacent between Lapland and Paris; the sixth, the northern parts of Asia where the cold in winter is intense; the seventh, North America, Japan, and China; and the eighth, all those mountains whose summits are covered with eternal snow[1472]. M. Latreille objects to this division, as too vague and arbitrary and not sufficiently correct as to temperature; and observes, with great truth, that as places where the temperature is the same, have different animals, it is impossible, in the actual state of our knowledge, to fix these distinctions of climates upon a solid basis. The different elevations of the soil above the level of the sea, its mineralogical composition, the varying quantity of its waters, the modifications which the mountains, by their extent, their height, and their direction, produce upon its temperature; the forests, larger or smaller, with which it may be covered; the effects of neighbouring climates upon it,--are all elements that render calculations on this subject very complicated, and throw a great degree of uncertainty over them[1473]. This learned Entomologist would judiciously consider entomological climates under another view,--that which the genera of _Arachnida_ and insects _exclusively_ appropriated to determinate spots or regions would supply[1474]. Linné's _dictum_ with regard to genera will here also apply; "Let the insects point out the climate, and not the climate the insects." If you expect invariably to find the same insects within the same parallels of latitude, you will be sadly disappointed; for, as our author further observes, "The totality or a very large number of _Arachnida_ and insects, the temperature and soil of whose country are the same, but widely separated, is in general, even if the countries are in the same parallel, composed of different species[1475]." The natural limits of a country,--as mountainous ranges, rivers, vast deserts, &c.,--often also say to its insect population, "No further shall ye come;" interposing a barrier that it never passes[1476]. Humboldt observes, with respect to the _Simulia_ and _Culices_ of South America, that their geographical distribution does not appear to depend solely on the _heat_ of the climate, the excess of humidity, or the thickness of forests; but on local circumstances that are difficult to characterize[1477]: and Mr. W. S. MacLeay makes a similar observation upon that of _Gymnopleurus_[1478]. So that the real insect climates, or those in which certain groups or species appear, may be regarded as fixed by the will of the CREATOR, rather than as certainly regulated by any _isothermal_ lines. Still, however, under certain limitations, it must be admitted that the temperature has much to do with the station of insects. The increase of caloric is always attended with a proportional increase in the number and kind of the groups and species of these beings. If we begin within the polar regions of ice and snow, the list is very meager. As we descend towards the line, their numbers keep gradually increasing, till they absolutely _swarm_ within the tropics. Something like this takes place in miniature upon _mountains_. Tournefort long since observed at the summit of Mount Ararat the plants of Lapland; a little lower, those of Sweden; next, as he descended, those of Germany, France, and Italy; and at the foot of the mountain, such as were natural to the soil of Armenia. And the same has been observed of insects. Those that inhabit the _plains_ of _northern_ regions have been found on the _mountains_ of more _southern_ ones; as the beautiful and common Swedish butterfly _Parnassius Apollo_, on the mountains of France, and _Prionus depsarius_ on those of Switzerland[1479].

M. Latreille, having given a rapid survey of the peculiar insect-productions of different countries, next attempts a division of the globe into _climates_, which he thinks may be made to agree with the present state of our knowledge, and be even applicable to future discoveries. He proposes dividing it primarily into _Arctic_ and _Antarctic_ climates, according as they are situated _above_ or _below_ the equinoctial line; and taking twelve degrees of latitude for each climate, he subdivides the whole into _twelve_ climates. Beginning at 84° N. L. he has _seven Arctic_ ones, which he names _polar_, _subpolar_, _superior_, _intermediate_, _supratropical_, _tropical_, and _equatorial_: but his _antarctic_ climates, as no land has been discovered below 60° S. L., amount only to _five_, beginning with the _equatorial_ and terminating with the _superior_. He proposes further to divide his climates into _subclimates_, by means of certain _meridian lines_; separating thus the _old_ world from the _new_, and subdividing the _former_ into two great portions,--an _eastern_, beginning with _India_, and a _western_, terminating with _Persia_. He proposes further that each climate should be considered as having 24° of longitude, as well as 12° of latitude[1480]. In this chart of insect Geography he states that he has endeavoured to make his climates agree with the actual distribution of insects[1481]; and it should seem that in many cases such an agreement actually does take place: yet the division of the globe into climates by _equivalent_ parallels and meridians, wears the appearance of an artificial and arbitrary system, rather than of one according with nature.

He has also pointed out another index to insect climates, borrowed from the _Flora_ of a country. Southern forms in Entomology, he observes, _commence_ where the _vine_ begins to prosper by the sole influence of the mean temperature; that they are _dominant_ where the _olive_ is cultivated; that species still _more_ southern are compatriots of the _orange_ and _palmetto_; and that some _equatorial_ genera accompany the _date_, the _sugar-cane_, the _indigo_ and _banana_[1482]. The idea is very ingenious, and, under certain limitations, supplies a useful and certain criterion. For though none of these plants are _universal_ in isothermal parallels of latitude; yet, as plants are more conspicuous than insects, the Entomologist, furnished with an index of this kind, may by it be directed in his researches for them; and in all countries in which there is a material change of the climate, as in France, there will be a proportional change in the _vegetable_ accompanied by one in the _insect_ productions.

ii. In considering the _range_ of insects I shall first advert to that of _individual_ species. At the extreme limits of phanerogamous vegetation we find a species of humble-bee (_Bombus arcticus_), which, though it is not known to leave the Arctic circle, has a very extensive range to the _westward_ of the meridian of Greenwich, having been traced from Greenland to Melville Island; while to the _eastward_ of that meridian it has not been met with. In Lapland its place appears to be occupied by _B. alpinus_ and _lapponicus_, with the former of which, though quite distinct, it was confounded by O. Fabricius; but whether these range further _eastward_ of that meridian has not been ascertained. From its being found in the Lapland _Alps_[1483], it may be conjectured that _B. alpinus_ ranges as high on this side as _B. arcticus_ on the other, and may perhaps be found in _Nova Zembla_. Some species that have been taken in Arctic regions are not confined to them. Of this kind is _Dytiscus marginalis_, which appears common in Greenland, abundant in Britain, and is dispersed over all Europe; while _D. latissimus_ is more confined, neither ranging so far to the north or south; and though found in Germany, not yet discovered in Britain. Other species have a still more extensive range, and are common to the old world and the new. Thus _Dermestes murinus_, _Brachinus crepitans_, _Tetyra scarabæoides_[1484], _Pentatoma juniperina_, _Cercopis spumaria_, _Vanessa Antiopa_, _Polyommatus Argiolus_, _Hesperia Comma_, _Vespa vulgaris_, _Ophion luteus_, _Helophilus pendulus_, _Oscinis Germinationis_, and many besides, though sometimes varying slightly[1485], inhabit both Britain and Canada: and though vast continents and oceans intervene between us, New Holland, and Japan; yet all have some insect productions in common. With the former we possess the painted-lady butterfly (_Cinthia Cardui_), with scarcely a varying streak: and Thunberg, in his list of Japan insects, has mentioned more than _forty_ species that are found also in this country. Whether any species has a _universal_ range may be doubted, unless indeed the flea and the louse may be excepted. On the other hand, some are confined within very narrow limits. _Apion Ulicis_ for instance, abundant upon _Ulex europæus_ in Britain, has not, I believe, been found upon that plant on the continent.

The geographical distribution of _groups_, is, however, far more interesting than that of _individual species_: for in considering this we see more evidently how certain _functions_ are devolved upon certain _forms_, and can scan the great plan of PROVIDENCE, in the creation of insects, more satisfactorily than by confining our attention to the latter. Groups, according to their range, may be denominated either _predominant_, _dominant_, _sub-dominant_, or _quiescent_.

1. M. Latreille has observed, that where the empire of _Flora_ ceases, there also terminates that of Zoology[1486]. _Phytiphagous_ animals can only exist where there are _plants_; and those that are _carnivorous_ and feed upon the _former_, must of necessity stop where they stop. Even the _gnat_, which extends its northern reign so high[1487], must cease at this limit; while, where vegetation is the richest and most abundant, there the animal productions, especially the insect, must be equally abundant. I call that, therefore, a _predominant_ group, members of which are found in all the countries between these points, or from the limits of animal-depasturing vegetation in the polar regions to the line.

Generally speaking, the _carnivorous_ insects, whether thalerophagous or saprophagous, are of this description. _Calosoma_, which devours Lepidopterous larvæ, though poor in species and individuals, is widely scattered. Captain Frankland found _C. calidum_ in his Arctic journey; _C. laterale_ and _curvipes_ inhabit tropical America[1488]: _C. Chinense_, as its name indicates, is Chinese[1489]; Mr. MacLeay has an undescribed species from New Holland; and _C. retusum_ was taken in Terra del Fuego. Another genus, equally universal and richer in numbers, is the lady-bird (_Coccinella_), which keeps within due limits the _Aphides_ of every climate from pole to pole. The _Libellulina_ pursue their prey both in Greenland and New Holland. The _saprophagous_ carnivora are also similarly predominant;--the _Silphidæ_, the _Dermestidæ_, the _Brachyptera_, the _Muscidæ_, prey on carcases wherever the action of the solar beam causes them to become putrid. Many of the above insects have probably their _capital_ station, or that where the species are most numerous, in or near the tropics; but the metropolis of the _Brachyptera_, at least as far as we can judge from our present catalogues, is within the temperate zone, particularly in Britain[1490]. The coprophagous _Petalocera_ are most abundant in the hottest climates; but the _Aphodiadæ_ form a predominant group: Professor Hooker took one species in Iceland[1491], and it probably ascends higher; others are found in India and China: but the metropolis of the group is within the temperate zone. Perhaps no genus is more completely universal than _Bombus_ (_Bremus_ Jur.), which, although its centre or _metropolis_ is likewise in the northern temperate zone, extends from Melville Island to the line. It is remarkable that some of the tropical _Bombi_ wear the external aspect of _Xylocopæ_, the kindred genus most prevalent in warm climates; and, _vice versâ_, some _Xylocopæ_ resemble _Bombi_. I have a Brazilian undescribed species of the latter genus, whose black body and violet-coloured wings would almost cause it to be mistaken for a variety of _X. violacea_; and _B. antiguensis_ and _caffrus_ F., (though their aspect belies it,) which misled Fabricius, are true _Xylocopæ_. I shall mention only one other predominant group, but that one of no common celebrity, formed of the gnats, or genus _Culex_. These piping pests, with their quiver--"venenatis gravida sagittis"--annoy man almost from the pole to the line. What remarkably distinguishes them, (as was formerly observed[1492],) and also the _Simulium_ or true mosquito,--they appear to prevail most in the coldest and the hottest climates, and the Laplander and the tropical American are equally their prey; while the inhabitants of the temperate zone, with some exceptions, suffer but little from them: so that they may be stated to have both an _arctic_ and a _tropical_ metropolis.

2. There are other groups which, though their empire extends to the tropics, fall short of the polar circles:--these I call _dominant_ groups. Of this description are some of the _Scarabæidæ_. _Onthophagus_ is found both in the old world and in the new, and in the temperate and torrid zones. Its principal seat appears to be within the tropics, but it may almost be said to have also a northern metropolis. More than one species have been taken in New Holland. In general, tropical insects exceed those of colder climates in _size_; but in the genus we are speaking of, the _European_ species are usually larger than the _Indian_. _Copris_ seems more abhorrent of cold than its near relation _Onthophagus_. _C. lunaris_, which ranges northward as far as Sweden, is the only recorded species found in Europe out of Spain. Latreille says, that all the large species of this genus are equinoctial: but _C. Tmolus_, described and figured by Fischer[1493], found in Asia near Orenburg, north of 50° N. L., is as big as _C. Gigas_ or _bucephalus_. Another dominant group of _Petalocera_, remarkable for the bulk and arms of its tropical species, are the mighty _Dynastidæ_, the giants and princes of the insect race. Though their metropolis is strictly tropical, yet the scouts of their host have wandered even as far as the south of Sweden, where one of them, _Oryctes nasicornis_, is extremely common. _O. Grypus_[1494] and some other species are found in South Europe; but though in a torpid state they can endure unhurt the severity of a Scandinavian winter, they cannot when revived stand the cold that often pinches Britons in the midst of summer, and therefore are unknown in our islands[1495]. The _Sphæridiadæ_, whose metropolis is within the northern temperate zone, extend from thence beyond the line, since Dr. Horsfield found two species in Java[1496]. It is probable, indeed, that this group is predominant. Some dominant groups begin at a lower latitude. Of this description are the carpenter-bees (_Xylocopa_), whose larvæ are preyed upon by that of the _Horiadæ_[1497] under _two_ forms, which extend from the tropics to about 50° N. L. Others are not common to both worlds. Thus, while _Cantharis_ is the gift of PROVIDENCE to America as well as the old world, _Mylabris_ is confined to the _latter_, where its range is very extensive;--in Europe, from South Russia to Italy and Spain; in Asia, from Siberia to India; and in Africa, from the shores of the Mediterranean to the Cape of Good Hope; which last continent, to judge from our present lists, especially the vicinity of the Cape, may be called the metropolis of the group[1498]. On the other hand, the _Rutelidæ_ and _Chlamys_, which have a range from Canada to the tropics, (within which is their metropolis,) are purely _American_ groups. Many more might be named under this head, but these will suffice for examples.

3. I call those _subdominant_ groups, which either never enter the tropics, or those tropical ones whose range does not exceed 50° of N. L. in the old world, or 43° in the new. I make this difference because, as M. Latreille observes, the southern insects which in Europe begin between 48° and 49° N. L., in America do not reach 43°.[1499] But though the winters in Canada, within the same parallel as France, are longer and more severe than those even of Great Britain or of Germany, yet the summers are intensely hot; so that though tropical _species_ do not range so high, those of a tropical _structure_, as Mr. W. S. MacLeay has intimated[1500], may be found at a higher latitude in the new world than in Europe.

The genus _Melöe_ affords an instance of a subdominant group of the first description. It ranges from Sweden to Spain and the shores of the Mediterranean, and seems a tribe almost confined to Europe, where it is not very unequally distributed. Of registered species Britain possesses the largest proportion; but Mr. W. S. MacLeay is of opinion that Spain is its true metropolis[1501]. I have a species of this genus, taken in North America by Professor Peck. The splendid genus _Carabus_ ranges still further north than _Melöe_[1502]. A very fine species (_C. cribellatus_) inhabits the polar regions of Siberia[1503]; but the metropolis of the group appears to be the temperate zone: some, however, have been found in northern Africa; and Sir Joseph Banks captured one in Terra del Fuego. Of those whose range is between the tropics and 50° N. L. we may begin with _Cicada_. One species, indeed, has been found by Mr. Bydder and others, a little higher, near the New Forest, Hampshire. We may take _Scolia_ for an example of a subdominant group beginning more southward. Its species first appear about 43° N. L., and abound in warm climates. In general most of those insects which M. Latreille denominates _meridional_,--such as _Scarabæus_, _Onitis_, _Brentus_, _Scarites_, _Mantis_, _Fulgora_, _Termes_, _Scorpio_, &c.--come under the present head, and in fact all tropical forms that wander to any distance within the above limits from their metropolis.

4. By _quiescent_ groups I mean those that have none, or no _high_ range as to latitude, from their centre or metropolis. I say as to _latitude_, because these groups have often an extensive one as to _longitude_. Thus, Mr. W. S. MacLeay has remarked to me, that _Goliathus_ appears to belt the globe, but not under _one_ form. The types of the genus are the vast African Goliaths (_G. giganteus_, &c.), which, as well as _G. Polyphemus_, and another brought from Java by Dr. Horsfield, have, like _Cetonia_[1504], the scapulars interposed between the posterior angles of the prothorax and the shoulders of the elytra[1505]: while the South American species (_G. micans_, &c.) have not this projection of the scapulars; in this resembling _Trichius_. Mr. MacLeay further observes, that the female of the Javanese _Goliathus_ is exactly a _Cetonia_, while that of the Brazilian is a _Trichius_. But quiescent groups have not generally this ample longitudinal range. Thus, _Euglossa_, in both its types,--one represented by _Eu. cordata_, and the other by _Eu. surinamensis_,--is confined to the tropical regions of America. _Doryphora_, likewise American, seems equally confined. _Asida_, though a _southern_ genus, is not found to enter the _tropics_; and _Manticora_ and _Pneumora_ are in nearly the same predicament.

Under the present head we may consider what may perhaps be denominated without much impropriety _endemial_ groups; by which I mean those groups that are regulated, as to their limits, not so much by the temperature, or the northing and southing of the latitude, as by the general aspect and circumstances of the country. Thus, the vast and nearly insular continent of _Africa_, almost as wide as it is long, and situated in or near the tropics, instead of inland seas or sea-like rivers, is intersected by parched sandy deserts, extending far and wide; circumstances which, though in the vicinity of its streams it is humid, impart an unusual degree of _aridity_ as well as heat to its general atmosphere; so that it well merits the poet's epithet, _Leonum arida nutrix_; and is also peculiarly fitted for all such animals, especially insects, as delight in a dry, sandy, hot country, particularly such as are predaceous in their habits. _America_, on the other hand, exhibits quite an opposite character. It is long, and comparatively narrow; surrounded, and almost divided into two continents, by immense circumfluent oceans; watered every where by rivers and lakes that emulate seas: in some parts covered by interminable forests; in others, intersected by ridges of the loftiest mountains. These circumstances, except in its Llanos, Pampas, or table-land, give a general character of humidity to its atmosphere, and fit it particularly for the production of a vast variety of peculiar plants, and for the residence of numerous and peculiar phytiphagous insects and other animals[1506]. Midway between these two continents lies a third (for so the vast island of New Holland may be denominated), which presents new features in its general aspect, and consequently new forms both in its _Flora_ and _Fauna_, mixed with many old ones parallel to those both of the new world and the old. Perhaps Europe and Asia, with several that are peculiar, agree more in their animal productions than the continents just described.

Let us next particularize a few of the peculiar types that distinguish particular continents and countries. The genera _Manticora_, _Graphipterus_, _Glaphyrus_, _Eurychora_, _Pneumora_, _Masaris_, and many others, are peculiar to Africa. In Asia alone we find _Mimela_[1507], _Euchlora_[1508], _Colliuris_, _Catascopus_[1509], _Apogonia_[1510], a peculiar type of _Horia_, &c. In America, _Agra_, _Galerita_, _Nilio_, another type of _Horia_, _Tetraonyx_, _Rutela_, _Doryphora_, _Alurnus_, _Erotylus_, _Scotinus_[1511], _Cupes_, _Corydalis_, _Labidus_, _Heliconius_, _Castnia_, &c. And in New Holland, _Helluo_, _Elephastomus_, _Anoplognathus_, _Diphucephala_[1512], _Cerapterus_, _Heleus_, _Adelium_, _Notoclea_, _Achilus_, _Thynnus_, _Nycterobius_, &c.

The countries bordering upon the Mediterranean, the Black, and the Caspian seas, agree in producing similar insects. These countries, and the Cape of Good Hope though so distant from them, appear to be the principal seat of Heteromerous _Coleoptera_, of the genera _Lixus_ and _Brachycerus_, and of the conical _Buprestes_[1513]. But the insects of Guiana, on one side the Cordilleras, differ from those of New Granada and Peru on the other; and similar differences are observed in other _neighbouring_ countries separated by natural boundaries.