Part 3
The notion of diminutive size, particularly as compared with vertebrate animals, seems more frequently attached to the idea of an insect than any other; and this notion is generally correct, for one insect that is bigger than the least of the above animals, thousands and thousands are vastly smaller: but there exist some that are considerably larger, whether we take length or bulk into consideration, and this in almost every order. To prove this most effectually, and that you may have a synoptical view of the comparative size of the larger insects of the different orders and tribes, I now lay before you a table of the dimensions of such of the largest as I have had an opportunity of measuring, including particularly those giants that are natives of the British isles.
Explanation of Table:
Column A - Length Inches B - Breadth Inches C - Expansion of Wings Longitudinal Inches} See note in table D - Expansion of Wings Transverse Inches }
_Order and | _Species._ | A | B | C | D | Family._ | | | | | | | | | | | | COLEOPTERA. | | | | | | | | | | | | CICINDELIDÆ |_Manticora grandis_ |1-5/8 | 7/10| | | | | | | | | ANTHIADÆ |_Anthia sexguttata_ |1-7/8 | 7/10| | | | | | | | | CARABIDÆ |_Carabus scabrosus_ |1-3/4 | 8/10| | | | | | | | | DYTISCIDÆ |_Dytiscus latissimus_|1-1/2 |1 | | | | | | | | | STAPHYLINIDÆ |_Staphylinus olens_ |1-1/2 | 5/10| | | | Br. | | | | | | | | | | | HYDROPHILIDÆ |_Hydrophilus piceus_ |1-3/4 | 7/8 | | | | Br. | | | | | | | | | | | BUPRESTIDÆ |_Buprestis grandis_ |2-1/2 |1 | | | | | | | | | |--------- _bicolor_ |2-5/12| 3/4 | | | | | | | | | DYNASTIDÆ |_Dynastes Hercules_ |4-1/2 |2-1/2 | | | | |Horns | | | | | |Incl. | | | | | | | | | | |_Megasoma Actæon_ K. |4-1/4 |2-1/4 | | | | |Horns | | | | | |Incl. | | | | | | | | | | CETONIADÆ |_Goliathus giganteus_|3-7/10|1-9/10| | | | | | | | | LUCANIDÆ |_Lucanus Cervus_ Br. |2 | 7/10| | | | |Mands.| | | | | |Incl. | | | | | | | | | | TENEBRIONIDÆ |_Tenebrio grandis_? |1-7/10| 7/10| | | | | | | | | BRENTIDÆ |_Brentus_ N. S. Mus. |2-1/10| 2/12| | | | MacLeay | | | | | | | | | | | CALANDRIDÆ |_Calandra_ N. S. Mus.|3-5/8 |1 | | | | MacLeay | | | | | | | | | | | BRACHYCERIDÆ |_Brachycerus apterus_|1-5/8 | 7/8 | | | | | | | | | |_Brachycerus_ |2 | 9/10| | | | _Toxicophagus_ | | | | | | Burch. | | | | | | | | | | | PRIONIDÆ |_Prionus grandis_ |6-1/2 |2-3/8 | | | | | | | | | |---- _cervicornis_ |5-1/2 |1-5/8 | | | | |Mands.| | | | | |Incl. | | | | | | | | | | |Do. |4-1/4 | | | | | |Mands.| | | | | |Excl. | | | | | | | | | | |---- _coriarius_ Br. |1-6/10| 7/10| | | | | | | | | LAMIADÆ |_Lamia grandis_ |2-3/4 |1 | | | | | |nearly| | | | | | | | | CHRYSOMELIDÆ |_Chrysomela_ N. S. |1-1/4 | 3/4 | | | | MacLeay | | | | | | | | | | | HISPIDÆ |_Alurnus grossus_ |1-3/10| 6/10| | | | | | | | | EROTYLIDÆ |_Erotylus grandis_ |1-6/10| 6/10| | | | |nearly| | | | | | | | | | | | | | | | DERMAPTERA. | | | | | | | | | | | | |_Labidura gigantea_ |1-1/4 | | | | | Br.? |nearly| | | | | |Forcs.| | | | | |Incl. | | | | | | | | | | |_Forficula_ N. S. N. |1-4/5 | 2/5 | | | | Holl. | | Do. | | | | | | | | | | | | | | | ORTHOPTERA. | | | | | | | | | | | | BLATTIDÆ |_Blatta gigantea_ |2-5/8 |1-1/2 | | | | | | | | | |---- N. S. MacLeay |3-3/10|1-1/2 | | | | | | | | | PHASMIDÆ |_Phasma grandis_ |7 | 7/8 | | | | |about | | | | | | | | | | |---- _australensis_ |8-1/2 | 3/4 |7-1/2 |2-3/4 | | K. | | | | | | | | | | | ACHETIDÆ |_Gryllotalpa |1-3/4 | | | | | vulgaris_ Br. | | | | | | | | | | | LOCUSTIDÆ |_Locusta Dux_ |4-3/8 | |8-1/4 |2 | | | | | | | CONOCEPHALIDÆ|_Acrida viridissima_ |2-1/10| | | | | Br. | | | | | | | | | | | | | | | | | HEMIPTERA. | | | | | | * | | | | | | | | | | | | FULGORIDÆ |_Fulgora laternaria_ |3 | |5-6/10|2 | | |nearly| | | | | | | | | | CICADIADÆ |_Cicada_ N. S. N. |2-1/10| |5-1/2 | | | Holland |Wings | | | | | |Excl. | | | | | | | | | | ** |Do. |2-8/10| | | | | |Wings | | | | | |Incl. | | | | | | | | | | NEPIDÆ |_Belostoma grandis_ |3 | |5-6/10|1-3/10| | | | | | | LYGEIDÆ |_Lygæus Pharaonis_ |2 |1 | | | | | | | | | | | | | | | LEPIDOPTERA | | | | | | * | | | | | | | | | | | | PAPILIONIDÆ |_Papilio Remus_ | | |8-3/4 |3-5/8 | | | | | | | |---- _Priamus_ |2-1/2 | |7-6/10|3 | | | | | | | |---- _Machaon_ Br. |1 | |3-1/2 |1-1/2 | | | | |nearly|Tail | | | | | |Excl. | | | | | | | NYMPHALIDÆ |_Morpho Teucer_ |1-7/10| |7-1/2 |4-1/2 | | | | | | | SPHINGIDÆ |_Sphinx_ N. S. Brazil|2-1/2 | 7/10|6-1/2 | | ** | | | | | | | | | | | | SPHINGIDÆ |_Sphinx Atropos_ Br. |2 | 5/8 |4-3/4 |1-1/2 | *** | | | | | | | | | | | | BOMBYCIDÆ |_Attacus Atlas_ |1-3/4 | |8-3/4 |5-1/2 | | | | | | | |_Gastropacha |1-1/4 | |3-1/2 |1-1/4 | | quercifolia_ Br. |nearly| | | | | | | | | | NOCTUIDÆ |_Erebus Strix_ |2 1/4 | |10-3/4|3-1/4 | | | | | | | | | | | | | NEUROPTERA. | | | | | | | | | | | | AGRIONIDÆ |_Agrion lineare_ |5-1/2 | |5 | | | | | | | | ÆSHNIDÆ |_Anax Imperator_ |3-1/3 | | | | | Leach--Br. | | | | | | | | | | | MYRMELEONIDÆ |_Myrmeleon |2 | |5 | | | libelluloides_ | | | | | | | | | | | SEMBLIDÆ |_Corydalis cornuta_ |2-3/4 | |5-1/4 | | | |Mands.| | | | | |Incl. | | | | | | | | | | |Do. |2 | | | | | |Mands.| | | | | |Excl. | | | | | | | | | | | | | | | | HYMENOPTERA. | | | | | | | | | | | | SCOLIADÆ |_Scolia cyanipennis_ |2 | | | | | | | | | | POMPILIDÆ |_Pompilus ocellatus_ |2-1/8 | |3-1/2 | | | | | | | | VESPIDÆ |_Cyclostoma grandis_ |2 | | | | | N. S. K. China | | | | | | | | | | | XYLOCOPIDÆ |_Xylocopa Nigrita_ |1-5/8 | | | | | | | | | | | | | | | | DIPTERA. | | | | | | | | | | | | TIPULIDÆ |_Tipula sinuata_ Br. |1-3/8 | |2-1/2 | | | | | | | | ASILIDÆ |New Gen. Brazil. |1-3/4 | | | | | | | | | | MUSCIDÆ |_Echinomyia grossa_ |3/4 | | | | | Br. | | | | | | | | | | | TABANIDÆ |_Tabanus_ N. S. Mus. |1-1/8 | | | | | Drury | | | | | | | | | | | |---- _bovinus_ Br. |1 | | | | | |nearly| | | | | | | | | | | | | | | | APTERA. | | | |_Expansion of| * | | | | Legs_ | | | | | Inches. | | | | | | SCOLOPENDRIDÆ|_Scolopendra_ N. S. |13 |7/8 | | | Mus. MacLeay | | | | ** | | | | | | | | | | IULIDÆ |_Iulus_ N. S. Do. |5-1/2 |8/10 | | | | | | | PHALANGIDÆ |_Gonyleptes_ N. S. | 3/8 | | 6 | | Brazil | | | | | | | | | _Class._ | | | | | | | | | | ARACHNIDA. | | | | | | | | | | SCORPIONIDÆ |_Scorpio_ N. S. |7 | | | | MacLeay |nearly| | | | |Chelæ | | | | |Excl. | | | | | | | | ARANEIDÆ |_Mygale_ N. S. Do. |3 |1-1/2 | 11 |
From this table you see that several insects included in it exceed some of the smallest _Vertebrata_ in bulk. In the _Mammalia_, the _Sorex Araneus_, called by the common people here the Ranny, is not more than two inches long excluding the tail; and the _Mus messorius_, or harvest-mouse, peculiar to the southern counties of England, is still more diminutive: so that to these little animals, the larger _Dynastidæ_, _Goliathi_, and _Prioni_, &c., appear giants, and may compete with the mole in size. Even some of the beetles of our own country, as the great _Hydrophilus_, the stag-beetle, &c., are more bulky than the two first-named quadrupeds. Amongst the birds, many _Picæ_, _Passeres_, &c., yield to several insects in dimensions, and their wings when expanded do not extend so far as those of not a few _Lepidoptera_. The great owl-moth of Brazil (_Erebus Strix_) in this respect is a larger fowl than the quail. Those beautiful little creatures, the humming-birds (_Trochilus_ L.), the peculiar ornament and life of tropical gardens, which emulate the most splendid butterflies in the brilliancy of their plumage, are smaller than a considerable number of insects in almost every order, and even than some of those that are natives of Britain. Various reptiles also are much inferior in size to many of the insects of the above table. The smallest lizard of this country would be outweighed by the great British beetles lately mentioned, and the mole-cricket (_Gryllotalpa vulgaris_); and some of the serpent tribe are smaller than the larger _Scolopendræ_ and _Iuli_. Amongst the _fishes_ also, though some are so enormous in bulk, others in this respect yield the palm to several insects. The _minnow_ and the _stickleback_ that frequent our own pools and streams are considerably inferior in size to some of our water beetles.
In looking over the table, and comparing the different species that compose it with each other, you will perceive that the largest insects of the two sections of _Hemiptera_, of the _Lepidoptera_ as to their _body_ merely, of the _Hymenoptera_ and _Diptera_, in general size fall considerably short of those of the other orders; and that certain individuals of the _Orthoptera_ and _Aptera_ bear away the palm in this respect from all the rest. In the _Coleoptera_ the giants, with the exception of the _Goliathi_, are chiefly to be found amongst the timber devourers in the _Lamellicorn_ and _Capricorn_ tribes. Of orthopterous insects the _Phasmidæ_ present the most striking examples of _magnitude_; and in the _Neuroptera_, the _Agrionidæ_ of great _length_.
It is worthy of remark here, that although the tropical species of a genus usually exceed those of colder climates in size, the _Gryllotalpa_ of Brazil is very considerably smaller than that of Europe: whether this is the case with the rest of the cricket tribe I have not had an opportunity of ascertaining. The _Lepidoptera_, though often remarkable for the vast expansion of their "sail-broad vans," if you consider only their bodies, never attain to gigantic bulk. Even the hawk-moths (_Sphinx_ L.), though usually very robust, make no approach to the size of the great beetles, or the length of some of the spectres (_Phasma_) and dragon-flies (_Agrionidæ_). With regard to the superficial contents of their wings, a considerable difference obtains in different species where they expand to the same length--for the _secondary_ wings are sometimes smaller than the _primary_, and sometimes they equal them in size. In some instances, also, the latter although long are narrow, and in others they are nearly as wide as long: regard, therefore, should be had to their expansion both ways. In the _Hymenoptera_ and _Diptera_, the principal giants are to be found in the predaceous or blood-sucking tribes, as _Scolia_, the _Sphecidæ_, _Pompilidæ_, _Vespidæ_, &c., belonging to the former order; and the _Asilidæ_ and _Tabanidæ_ to the latter. The true and false humble bees (_Bombus_ and _Xylocopa_) and the fly tribe (_Muscidæ_), though they sometimes attain to considerable size, scarcely afford an exception to this observation. Amongst the _Aptera_ none of the _Hexapods_ strike us by their magnitude, and few of the _Octopods_, though the legs of some of the _Phalangidæ_ inclose a vast area. That in the table would with them describe a circle of six inches diameter, though its body is little more than a quarter of an inch in length. The _Myriapods_ exceed most insects in the vast elongation of their body, which with their motion gives them no slight resemblance to the serpents. In the class _Arachnida_, the bird-spiders (_Mygale_) are amongst the principal giants, nor do the _Scorpions_ fall far short of them--both of them when alive often alarming the beholder as much by their size as by their aspect.
But as I have before observed, generally speaking, one of the most remarkable characters of the insect world, is the little space they occupy; for though they touch the vertebrate animals and even quadrupeds by their giants, yet more commonly in this feature they go the contrary way, and by their smallest species reach the confines of those microscopic tribes that are at the bottom of the scale of animal life. I possess an undescribed beetle, allied to _Silpha minutissima_ E. B.[50], which, though furnished with elytra, wings, antennæ, legs, and every other organ usually found in the order it belongs to, is absolutely not bigger than the full stop that closes this period. In several other coleopterous genera there are also very minute species, as in _Cryptophagus_, _Anisotoma_, _Agathidium_, &c. I know no _orthopterous_ insect that can be called extremely minute, except that remarkable one found on the Continent in the nests of ants, the _Blatta Acervorum_ of Panzer[51], but now called, I believe, _Myrmecophilus_: nor indeed any in the _Hemiptera_, _Neuroptera_, and _Diptera_, that approach the extreme limits of visibility: but in the _Lepidoptera_, the pygmy _Tinea occultella_ is almost invisible except in flight, being scarcely thicker than a horse's hair, and proportionably short; indeed, many others of those lovely Lilliputians, the subcutaneous _Tineæ_, decorated with bands of gold and silver, and studded with gems and pearls, that in larger species would dazzle the beholder's eye, are in size not much more conspicuous. In the _Hymenoptera_ order, _Ichneumon Punctum_ of Dr. Shaw, which forms so striking a contrast to his giant _Phasma dilatatum_, being placed together in the same plate; and another that I possess, under the trivial name of _Atomos_, would elude the searching eye of the entomologist unless when moving upon glass. Linné named the tribe of parasites to which these belong, _Minuti_, on account of their generally diminutive size. But these little minims, under the superintendence of Providence, are amongst the greatest benefactors of the human race, since they keep within due bounds the various destroyers of our produce.
The number of minute species of insects seems greatly to exceed that of large ones, at least in Europe, of which it may be asserted probably with truth, that two-thirds are under a quarter of an inch in length, and one-third not exceeding much a duodecimal of it. It might hold good perhaps in _Coleoptera_, _Hymenoptera_, _Diptera_, and _Aptera_: but in _Orthoptera_, _Hemiptera_, _Neuroptera_, and especially _Lepidoptera_, a large proportion would be found to exceed three lines in length. Neither can it be affirmed of extra-European species, of those at least preserved in cabinets, amongst which it is rare to find an insect less than the fourth of an inch long. This, however, must probably be attributed to the inattention of collectors, who neglect the more minute species.
* * * * *
Though size forms a pretty accurate distinction between insects and the great bulk of _vertebrate_ animals, it affords less assistance in separating them from the _invertebrate_ classes, which are of every size, from the monstrous bulk of some _Cephalopoda_ (cuttle-fish) and _Mollusca_ (shell-fish, &c.) to the invisible infusory animalcule: but external characters, abundantly sufficient for this purpose, may be drawn from the general covering, substance, form, parts, and organs of the body. As I shall enter into pretty full details upon this subject when I come to treat of the external anatomy of insects, I shall here, therefore, only give such a slight and general sketch of the distinctions just mentioned, as will answer the end I have in view. I must here repeat what I have before observed, and what it is necessary that you should always bear in mind, namely, that at the limits of classes and of every other natural group, the characters begin to change, those peculiar to the one group beginning gradually to disappear, and those of the other to show themselves; so that it is impossible almost to draw up a set of characters so precise as exactly in every respect to suit all the members of any natural group.
Whichever way we turn our eyes on the objects of creation, above--below--athwart, _analogies_ meet us in every direction, and it appears clear, that the Book of Nature is a Book of Symbols, in which one thing represents another in endless alternation. And not only does one animal, &c. symbolize another, but even between the parts and organs of one set of animals there is often an _analogy_ as to their _situation_ and _use_, when there is little or no _affinity_ as to their _structure_--or again, the analogy is in their _situation_, without affinity in either structure or use. Thus certain parts in one tribe represent other certain parts of another tribe, though as to their structure there is often a striking disagreement. This is particularly observable between the vertebrate and invertebrate animals. I shall therefore, in my remarks on the general and particular structure of insects, contrast it in its most important points with that of the first-mentioned tribe.
The first thing that strikes us when we look at an insect is its outside _covering_, or the case that incloses its muscles and internal organs. If we examine it attentively, we find that it is not like the skin of quadrupeds and other _Vertebrata_, covering the whole external surface of the body; but that in the large majority it consists of several pieces or joints, in this respect resembling the skeleton of the animals just named; and that even in those in which the body appears to have no such segments, as in many of the Mites (_Acarus_ L.), they are to be found in the _limbs_. This last circumstance, to have externally jointed legs, is the peculiar and most general distinction by which the _Insecta_ of Linné, including the _Crustacea_, may always be known from the other invertebrate animals[52].
If we proceed further to examine the _substance_ of this crust or covering, though varying in hardness, we shall find it in most cases, if we exclude from our consideration the shells of the _Mollusca_, &c., better calculated to resist pressure than that of the majority of animals that have no spine. In all the invertebrate tribes, indeed, the muscles, there being no internal skeleton, are attached to this skin or its processes, which of course is firmer than the internal substance; but in insects it is very often rigid and horny, and partially difficult to perforate, seldom exhibiting that softness and flexibility which is found in the cuticle of birds and most quadrupeds. From this conformation it has been sometimes said, that insects carry their _bones_ on the _outside_ of their body, or have an _external_ skeleton. This idea, though not correct in all respects, is strictly so in this--that it affords a general point of support to the muscles, and the whole structure is erected upon it, or rather I should say within it. The difference here between _Insects_ and the _Vertebrata_ seems very wide; but some of the latter make an approach towards it. I allude to the Chelonian Reptiles (_Testudo_ L.), in which the vertebral column becomes external or merges in the upper shell. The _cyclostomous_ fishes also are not very wide of insects as to their integument. But on this subject I shall be more full hereafter.
The _forms_ of insects are so infinitely diversified that they almost distance our powers of conception: in this respect they seem to exceed the fishes and other inhabitants of the ocean, so that endless diversity may be regarded as one of their distinctions. But on all their variations of form the Creator has set his seal of symmetry; so that, if we meet with an animal in the lower orders in which the parts are not symmetrical, we may conclude in general that it is no insect.
But it is by their _parts_ and _organs_ that insects may be most readily distinguished. In the _vertebrate_ animals, the body is usually considered as divided into _head_, _trunk_, and _limbs_, the _abdomen_ forming no part of the skeleton; but in the _insect_ tribes, besides the organs of sense and motion, the body consists of _three_ principal parts--_Head_, _Trunk_, and _Abdomen_--the _first_, as was before observed, bearing the principal organs of _sense_ and _manducation_; the _second_ most commonly those of _motion_; and the third those of _generation_--the organs of respiration being usually common to both trunk and abdomen. These three primary parts,--though in some insects the head is not separated from the trunk by any suture, as for instance in the _Arachnida_; and in others, head, trunk, and abdomen form only _one_ piece, as in some mites,--still exist in all, and in the great majority they are separated by incisures more or less deeply marked: this is particularly visible in the _Hymenoptera_ and _Diptera_, which, in this respect, are formed upon a common model; and in the rest, with the above exceptions, it may be distinctly traced.