Having thus given you some, though an imperfect account, of the geographical distribution of insects, I am next to say something concerning their local distribution in any district, or their favourite haunts; a knowledge of which, with respect to those of our own country, is indispensable to the collector.
The surface of a country consists either of mountains, hills and valleys, or of plains. It is diversified by forest, wood, or copse; and watered by rivers, rivulets, lakes, and pools. Those parts that are not clothed with wood are either open or inclosed, forming grassy downs, heaths, pastures, meadows, morasses, and arable land. The soil also is equally various:—we find clay, loam, marl, chalk, vegetable mould, moor, sand, &c. The mountains and hills are either covered with a stratum of soil, or are rocky and bare; the arable lands are divided by living or dead fences, the latter formed of various materials,—or else they are open, and the property only marked out by grassy balks, &c. All these places abound in shrubs and plants; some local, and some generally distributed. But besides the land and its fresh waters, we must look also to the sea, and its sandy, pebbly, or rocky shores, and the sea-wrack that is cast up upon them; the estuaries that receive its tides; the brackish waters and saline marshes in its vicinity. All the above places, when opportunity serves, the Entomologist should explore, for in almost all he will find peculiar kinds of insects.
As mountains and hills have usually their own Flora, the insects appropriated to alpine plants can only be met with where the pabulum is found. Here also those northern insects that are impatient of a warmer climate will take their station, if they migrate to the southward[1518]. The predaceous beetles likewise sometimes frequent a mountainous district. Carabus glabratus was first taken by Professor Hooker on Ingleborough; and probably, if the Welsh and Scotch mountains were duly investigated by an Entomologist, many novelties would reward his toils. The valleys and plains, especially those of a sunny exposition, abound in insects. When the heat of the atmosphere indisposes you for motion, you will find it no unprofitable or unpleasant employment, lying on the grass, to search for minute beetles, which you will there find coursing about amongst the tufts and roots of the herbage. Thus you may procure many of the Pselaphidæ, which you would not otherwise meet with. Even when the grass is grown up, insects are fond of alighting upon its spikes, and thence drop or run to the ground. Should circumstances ever carry you abroad to the steppes or grassy plains of Tartary, or to Hungary, you would find there two or three species of the singular genus Lethrus, which burrows in the soil. Every hole is inhabited by a male and female;—from it they issue to attack the plants or vines; and having cut out the heart of a plant, go backwards like a crab with the prize to their burrow. At the time of pairing, sometimes violent battles, encouraged by the female, take place between the male and a stranger of that sex desirous of admission, which cease only with the death or flight of the stranger[1519]. The vicinity and borders of woods generally abound in insects of every Order; and if you proceed, as hereafter directed, will furnish you with numerous prizes, especially of Lepidoptera. Here alone you can meet with the purple emperor butterfly (Apatura Iris); and if properly equipped you may readily secure him.
The waters you will find nearly as prolific in insects as the land. In them, amongst the beetles, you may expect to meet with Dytiscus, Haliplus, Pælobius, Hyphydrus, Hydroporus, Noterus, Colymbetes, and other Dytiscidæ; the Gyrini, Hydrophili, Hydrænæ, Elophori, &c.: under stones, the Elmis; and in the mud, the Parni and Heteroceri. Some Sphæridiadæ are also aquatic: I have taken more than once Cercyon hæmorrhoidale from the under side of a piece of wood immersed in a canal[1520]. Even a few of the weevil tribes are to be met with in water. Lixus paraplecticus, Tanysphyrus Lemnæ, Bagous atrirostris, are of this description. A species of Ceutorhynchus of Germar's third family (C. Natator K.) swims well. On aquatic plants you must look for Helodes and the splendid Donaciæ, which, living on submerged shoots and roots of these plants in their larva state, continue to attend them when perfect. Amongst the Eutrechina[1521],—Elaphrus, Notiophilus, and Bembidium frequent humid places, as the banks of rivers and ponds; and in such a station, under the roots of Potentilla anserina, Polygonum, &c. if you should be fortunate enough to find Omophron limbatum, which connects the Eutrechina with the Eunechina, you will make a valuable addition to the list of British insects. In the waters also you will meet with many Heteropterous Hemiptera; as Gerris, Hydrometra, and Velia, and all the Hydrocorisæ or water-bugs. On aquatic plants the larvæ of some Lepidoptera feed, as Hydrocampa stratiotata, potamogata, &c. Those also of the Trichoptera must be sought for in the water: and if you should feel inclined to see an interesting collection of their very curious cases, Mr. Sheppard of Wrabness can gratify your curiosity. Though few or no Hymenoptera frequent this element, vast numbers of Diptera are there alone to be met with in their preparatory state, particularly the gnats. We learn from Humboldt a curious fact with respect to those of South America, or the Zancudos; that, with some exceptions, these pests do not frequent those rivers called by the natives black waters, but only those which they name white waters[1522]. Of the Aptera, the genera Hydrachna, Eylaïs and Limnochares are purely aquatic. Several spiders will walk over the water; and one species (Argyroneta aquatica) inhabits it[1523]. The stagnant waters in your vicinity will produce different species from running ones. Thus Haliplus elevatus, &c. inhabits only the latter, while the majority of the Dytiscidæ abound most in the former: the more minute ones may be sought for with success amongst the duckweed that covers a pool. I do not recollect finding any insect in waters absolutely salt[1524]; but brackish waters produce peculiar species: in these only, Hydræna marina occurs; and many of those large-eyed Cimicidæ (Acanthia), as A. saltatoria, littoralis, and Zosteræ occur in places where salt water has been. Latreille observes, that the genus Pimelia is to be met with only where the soil is impregnated with saline particles, or where the species of the genus Salsola abound[1525].
Heaths, though they do not afford numerous insects, have their rarities. Cicindela sylvatica, Carabus nitens and arvensis, frequent them, and are not elsewhere to be seen. Curculio nebulosus is also to be found on them, in places where the turf has been peeled; and some scarce Lepidoptera. In their vicinity, in sunny sandy banks, some of the rarer Ammophilæ and Pompili may be taken; and it is here only that I have ever met with Panurgus[1526]. Meadows and pastures are not to be neglected. Early in the year, when they are yellow with the blossoms of Ranunculus bulbosus, Leontodon Taraxacum, &c., many minute beetles, and not a few Hymenoptera and Diptera, frequent them. Morasses also have their peculiar insects. In these you will meet with some of the scarcer Eutrechina; as Chlænia holosericea and nigricornis, Blethisa multipunctata, various Bembidia, &c. In this kind of district in the Isle of Ely Aphodius plagiatus has been taken, and that scarce and beautiful butterfly Lycæna Virgaureæ. Where land is cultivated the Entomologist as well as the farmer may expect a harvest. Insects in general are fond of perching on the summit of a blade of grass or corn; and many minute ones may be taken coursing about in the ears of the latter: some to devour the fungilli that infest the grain, as Phalacrus corruscus in Reticularia Segetum; others to attack the grain itself, as Cecidomyia Tritici; others to destroy these destroyers, as three little parasites belonging to the Chalcidites[1527]. But I have already mentioned most of those insects that are to be expected in such situations[1528]: I shall therefore only further observe, that upon barley particularly you will meet with the species of Latreille's genus Cephus.
With respect to soils, those that are light appear to be most prolific in insects. Warm sandy banks are frequented by Cicindela campestris, Opatrum sabulosum, Helops quisquilius, &c.: in them (when of a southern aspect) Ammophilæ, Pompili, and numerous Hymenoptera nidificate. Chalk also attracts various insects. Latreille observes, that the Licini, Papilio Cleopatra, several species of Dasytes, and some Lamiæ, delight in this kind of soil[1529]:—in my own neighbourhood I have observed Polyommatus Corydon principally in chalk-pits. One of these pits, under a wood in an adjoining parish, has produced me several valuable insects. Here I took Apion ebeninum, Orobitis globosus, a new species of Evæsthetus, several of the rarer Pselaphidæ and Cholevæ, and Chætophorus cretifer before noticed[1530]. I do not mean, however, that all these are properly chalk insects; but they fall into these pits, where they are readily discerned, from the contrast of their colours with the whiteness of the chalk. By watching attentively the bottom of one, vast numbers in a warm day may be taken when they fall or are climbing upwards. Of all soils clay offers the fewest inducements to the Entomologist, who will lose both his time and labour in a clay-pit; while in one of sand, chalk, or marl, they will usually not be mispent. Vegetable earth also affords a harbour to various larvæ, and the pupæ of many nightfliers amongst the Lepidoptera, by digging in it, especially under trees, may be obtained. Even the bare rocks have their insect frequenters that take shelter in their fissures; and in the early part of your career especially you should always turn over large stones, as beneath them many of the Harpalidæ and other Eutrechina frequently lie hid: and in this situation, both in Suffolk and Sussex, Lomechusa emarginata, one of our scarcest Brachyptera, has been taken. Old trees also, and planks that have laid long without being moved, often afford a shelter to many of the minute Coleoptera; as Pselaphidæ, Aleocharidæ, Cryptophagidæ, Scymnidæ, &c. Live fences, especially when the hawthorn is in blossom, and where trees are also intermixed, are attended by innumerable insects of almost every description; and even the black-thorn will present you with one of our most splendid weevils (Rhynchites Bacchus). Dead fences are almost as fertile in insects as living ones. In gates, posts, rails, and other timber when felled, the timber-devouring tribes take their station:—between the bark and the wood are the Bostrichidæ; in the wood itself, the Anobidæ and the Capricorn beetles. Here also you may meet with many Hymenoptera, which either devour timber or nidificate in it,—as the Siricidæ, Chelostoma, Trypoxylon, Sapyga, and several Diptera. In the decaying hedgestakes and sticks, where the Sphæria decorticans has turned off the bark, you may meet with Anthribus brevirostris; with A. latirostris, and other beetles, in S. fraxinea; and A. albinus, which I have more than once captured as it was emerging from the fissure of a gate-post, probably feeds on some internal fungus. The grassy balks that separate open fields usually abound in umbelliferous plants, which are attended by numerous Hymenoptera and Diptera, particularly by the various species of the splendid tribe of Chrysidæ: and the grassy banks of fences, where the aspect is sunny, are generally bored by a variety of insects of the former Order, to prepare a nest for their young. Andrenidæ and Nomadidæ particularly select this situation, the latter probably depositing their eggs in the burrows of the former[1531]. By watching these places in the spring, you may perhaps have the good fortune to meet with a Stylops. It is singular, that some insects choose, for their own residence or that of their young, the hardest and most trodden pathways. Thus, some ants will build their subterranean apartments under gravel walks; and so do many species of the genus Halictus[1532], the habits and economy of which have been so ably detailed by M. Walckenaër[1533]: Cerceris also, and other Hymenoptera, will choose such places, however public, for the site of their nests or burrows. The ground is so consolidated by the constant foot, that they, probably find such situations spare them a world of labour, and therefore in their choice balance one inconvenience by another.
Though the sea itself, I believe, produces no true insects, yet there are many that constantly or occasionally haunt its shores. On the sand-hills of the Norfolk coast I found Ægialia globosa and Cicindela hybrida. Ceutorhynchus horridus inhabits thistles that grow near the sea. Under the Zostera and Fuci, (cast up both on its beach and the shores of estuaries,) many peculiar species of Cercyon, several Aphodii, and numerous Brachyptera, may often be found. In this situation the rare and singular Bledius armatus has been taken. At certain seasons of the year the beach and environs of the sea are covered by many species of Coccinella, which seem to bend their course thither from the inland country, as if they were about to emigrate[1534]. When the weather is fine and the tide begins to retire, at the line of its highest rise I have taken on the eastern coast a variety of insects, and amongst the rest Anomala Frischii. The inundations of rivers, except in the depth of winter, always bring a number of these little creatures, which float on the surface on bits of stick, weeds, &c.; and where they deposit these articles when the water begins to subside, you may generally reap a plentiful harvest of various kinds.
You see, now, how varied is the scenery to which the diversion of the Entomologist introduces him; that he is never out of his way: whether on hill or in valley; on upland or plain; on the heath or in the forest; on the land or on the water; in the heart of a country or on its shores;—still his game is within his reach. But in order to enable him to pursue it with greater prospect of success, he must recollect that not only is every face of the country to be explored, but both the plants and the animals that it produces; and that he must not turn with disgust from even the carcase or the excrement of the latter. As numerous species of herbivorous insects feed only on one kind of plant, the Entomologist, when he discovers a scarce one, should examine it with the hope of finding upon it a scarce insect. Sometimes it happens that only a single opportunity occurs in a man's life of seeing certain plants growing wild: such opportunities should never be neglected. Some insects also inhabit a plant in one district or season, and not in another. Thus the most beautiful of the Apions, A. Limonii[1535], though the plant it feeds upon usually abounds near the sea, I have discovered only on the northern coast of Norfolk; and another scarcely less beautiful, but more minute (A. Astragali[1536]), though I have sought for it year after year, Astragalus glyciphyllus being abundant near me, I never found but once. The blossoms of plants as well as the leaves must be inspected. In those of the rose, the Cetonia aurata is often taken[1537]; and in the bells of the different species of Campanula various bees may be captured enjoying a luxurious repose[1538]. No vegetable productions abound more in insect inhabitants than the Fungi. In Agarics several Diptera are to be taken, many Aleocharæ, Oxypori, &c.; in Boleti, the various species of Mycetophagus; in the arboreous ones, and under bark, more than one kind of Ips; and in Auricularia, as well as Boletus, the whole genus Cis. Upon living Vertebrate animals you must look for Pulices, Pediculi, Nirmi, Acari, and many Diptera, as Œstrus, Tabanus, Stomoxys, and the Pupipara of Latreille; and on the garden-snails for that curious genus Drilus, and some Acari[1539]. The caterpillars and pupæ of Lepidoptera, &c. will, as you have heard, furnish you with numerous ichneumons[1540]. On dead animals you will find the various species of Silphidæ, Nitidulidæ, Dermestidæ, Byrrhidæ, Chlolevidæ, Staphilinidæ, Muscidæ, &c.; and in excrement, various Scarabæidæ, Histeridæ, Aphodiadæ, Sphæridiadæ, the Brachyptera in general, and several Diptera[1541]. In putrescent roots and fruits, as the turnip, the cucumber, &c., you may also occasionally meet with rare Coleoptera.