I must next say something upon the seasons of insects, and their times of appearance. Those that collect honey and pollen are generally among the first that proclaim the approach of spring; and their appearance may be dated from the blossoming of certain trees and plants of common occurrence. Other plants, accompanied by peculiar insects, blossom later; and so on till we arrive at the autumn. The earliest insect-season commences with the flowering of the sallow (Salix Caprea) usually accompanied in the garden by that of the crocus and the gooseberry. Then is your time to collect many species of wild bees and Diptera not afterwards to be met with: and various other insects now begin to emerge from their winter-quarters, or are produced from the pupa. Another and later season is marked by the general blossoming of the butter-cup (Ranunculus bulbosus), accompanied by the marsh-marygold (Caltha palustris) and ladies'-smock (Cardamine pratensis); when you may hunt the pastures, meadows, and marshes with success, and take some insects that do not show themselves later. The coprophagous insects are now abundant. Amongst others, Aphodius testudinarius, a perfectly vernal species, is now only to be taken, and usually flying. A third insect-season indicated by Flora, and a very prolific one, commences with the blossoming of the hawthorn, when you must desert the meads for the inclosures. At this time all nature begins to put on her gayest attire, and all her insect tribes are now on the alert, and fill the air. They are almost universally attracted by the sweet and lovely blossoms of the plant just named: so that by examining them you may entrap some of every Order, and many that during the year will appear no more. Even many of the saprophagous insects will sip nectar from these flowers. The umbelliferous plants proclaim the fourth season of insects, particularly the wild carrot and parsnip. You will scarcely ever fail to find, if the weather is genial, Hymenopterous and Dipterous insects of various genera,—especially such as have a short tongue,—engaged in collecting the honey from those plants. Here you may take some of the rarer Chrysidæ, Crabronidæ, Cercerides, &c., and occasionally even Coleoptera. The last insect-season may be dated from the general flowering of the thistle tribe. When these are in blossom is the best time of all to collect the humble-bees (Bombus[1542]), the leaf-cutter bees (Megachile[1543]), and many other Apiariæ, which alone by their long tongues can imbibe the honey and collect the pollen of these flowers. The male humble-bees frequent them to the last, and often seem as if they were intoxicated with their sweets.
But perhaps you may prefer considering the whole summer appearance of insects as divided into three principal seasons. This may thus be done. Their vernal season may commence Florente Caprea, and end Florente Oxyacantha; their summer, Florente Oxyacantha and Florentibus Umbellatis; their autumn, Florentibus Umbellatis and Florente Carduo. In the first, the number of insects will be daily increasing; in the second (which is the harvest of the Entomologist, when his eyes and his hands ought to be every where), they will reach their utmost complement; and in the third, they will be gradually decreasing in number, till they generally die, or go into winter-quarters. At this time many minute Diptera and Ichneumons take shelter from the weather in the windows of our apartments. These seasons will not always exactly correspond with our usual reckoning, and take place at the same time; since, being regulated by our varying temperature, they will be sometimes sooner and sometimes later, sometimes longer and sometimes shorter. Though I have not named a brumal season, because insects are in winter usually torpid,—yet some, as Diurnea Novembris, Cheimatobia brumata, and many Tipulariæ, even then make their appearance.
If you ask, Whether it be not possible to regulate our Entomological seasons by the appearance of insects themselves? I should answer, that probably this might be done; but that further observations seem wanted to enable us to do it satisfactorily. Perhaps the appearance of Formica rufa beginning the business of the year might form the commencement of one season; the flight of the orange-tip butterfly (Pontia Cardamines[1544]), of a second; a third might be indicated by the swarming of Melolontha vulgaris; a fourth, by that of Amphimalla solstitialis; and the last, by the appearance in numbers of Aphodius ciliaris, which in the autumn fills every horse-dropping.
Some insects are so ephemeral, that they are to be found in numbers only for a few days, and then disappear for that season. Of this description are the Ephemeræ, much of whose history has been detailed to you. Those of which De Geer has given an account (E. vulgata) appeared about the end of May or the beginning of June, and continued about a fortnight[1545]; while those which Swammerdam observed did not come forth till the middle of June, and lasted only three days[1546]. The same period distinguished those of which Reaumur has compiled so interesting a history, but they did not show themselves before the middle of August[1547]. My kind friend Mr. Marsham not long before his death copied for me some memoranda he had made with respect to the sudden appearance of Cercopis bifasciata. On one occasion the white dress of a lady sitting upon a haycock was covered by these insects; but on the following day the same steps were taken at the same time to procure some, when after the most diligent search not a single one could be found. The same circumstance was observed a few years afterwards by another friend of his. He himself was of opinion that the insects in question were then migrating[1548].
I may here observe, that the London amateurs have particular seasons for collecting moths. For the imago they go into the woods in April, May, June, and October. For the larvæ they take the beginning of April, June, the beginning of July, and September. They dig for pupæ late in July, and in January and February.
I shall lastly make a few observations upon the times of action and repose of insects, the knowledge of which, as far as it can be obtained, is of essential use to the industrious collector. Entomologists have divided the Lepidoptera, with a view to this circumstance, into diurnal, crepuscular, and nocturnal; or butterflies (Papilio L.), hawkmoths (Sphinx L.), and moths (Phalæna L.). These terms may be applied to insects in general.
i. Diurnal insects are abundant. Butterflies in particular fly generally at no other time: they accompany the sun in his course, and before he sets disappear. Some other Lepidoptera, though not so named, are day insects:—such are the Zygænidæ, &c. amongst the hawkmoths; and amongst the moths, Plusia Gamma, the Phytometræ solares of Haworth[1549], and some others. Numberless Coleoptera belong to this section. The Donaciæ fly only when the sun is out and the air is warm; they are then extremely agile and difficult to take. Some Hopliæ swarm in the day before noon, and then disappear[1550]: most of the tetramerous beetles also appear to be diurnal. The Libellulina and many other Neuroptera may also be so termed; and the Hymenoptera almost universally, with the sole exception of the Formicidæ[1551]. Amongst the Diptera, if we leave out the Tipulariæ, the rest will be found for the most part to belong to the present section.
ii. Crepuscular insects, strictly speaking, are those that appear only during the twilight, whether in the morning or evening; but the term may be understood, with some latitude, to signify all those insects that are seen only in the morning and evening, though after sunrise and before sunset. Of these, some come forth only in the morning, others only in the evening, and others both morning and evening. My memory only furnishes me with a single instance of an insect whose principal appearance and flight are in the morning. Catocala nupta I have often seen flying at this time, about six or seven o'clock, and never at any other: I am not however prepared to assert that it does not appear in the evening or night, but I have then never met with it. In the evening more particularly you hear the hum of the dung-beetle (Geotrupes), which Linné thought the prognostic of a following fine day; and of the swarms of Melolontha vulgaris and Amphimalla solstitialis. Then also many other Coleoptera are in the air; especially before a thunderstorm, a state of the atmosphere that particularly excites insects[1552]: Ptinus imperialis and germanus I have never taken except under these circumstances. Then the Ephemeræ sport in the air, and lead their mystic dance. The majority of the hawkmoths are then too on the wing, with their long tongues imbibing the nectar of the flowers while they hover over them, both morning and evening.
iii. In the night the main body of the moths take their flight, as well as a vast number of Coleoptera and insects of other orders. At this time the Blattæ and crickets leave their hiding-places and run about: but the other Grylli L., though they sing in the night, fly only in the day. Then also the Carabi, like beasts of prey, leave their dark retreats,—in this differing from the Cicindelæ, which are diurnal,—and prowl about to entrap other unwary insects. Then, likewise, the female glowworm hangs out her lamp of love, and the male, led by it, wings his way to her: and then the water-beetles (Dytisci, Gyrini, &c.) forsake the waves and become tenants of the air.