Part 6

There are few points about which we know less than the causes of distribution and rarity, although there are certain tolerably well recognized laws which govern the occurrence of some species in certain localities. What I mean is that marshy spots, say salt marshes for instance, attract certain beetles and bugs which are never found except in such places; certain kinds of flowers attract bees which never appear to visit any others, but these localities and kinds of flowers occur often at great distances from each other, and why--given a certain flower you probably find a certain bee peculiar to it; or given a certain kind of marsh you probably find a certain beetle, although the localities may be hundreds of miles apart--I think still awaits explanation. I will give an example with which I am personally well acquainted. {106} There is a rare little bee (_Macropis labiata_) which at one time was looked upon as an extreme rarity, having only occurred three or four times in this country. Mr. F. Enoch, comparatively lately, took a fair number on the flowers of the greater loose-strife (_Lysimachia vulgaris_) along the canal at Woking; now that its food-plant is known, it has occurred in several other places in numbers, and no doubt wherever the _Lysimachia_ is abundant _Macropis_ will probably occur, but how the little creature has been distributed over the places where this plant occurs, which are often far distant from each other, seems to me to be an unsolved problem. Then there is another puzzling point, and that is the extreme rarity of certain insects. No doubt in many cases this is due to ignorance of their habits, as it has frequently happened that species once considered of great rarity have occurred in abundance when their habits have been discovered, as in the case of _Macropis_, but there are some cases which do not seem to be explainable in this way. I will again give an example which has been specially under my own observation. _Dufourea vulgaris_, a little black bee, {107} which certainly might not be recognized from its outward appearance, as there are many which very closely resemble it, is still one of our greatest rarities, only three British examples having been recorded. The first was taken by Sir Sidney Saunders at Chewton, Hants, on the twelfth of August, 1879; this was a male; the second, a female, was taken by Mr. T. R. Billups at Woking, on the first of August, 1881; and the third by myself at Chobham (about four miles from Woking) on the first of August, 1891. I believe in all cases these were taken on yellow composite flowers. The flight and behaviour of the male I caught were so peculiar, as it wriggled itself into the flower, that I knew at once I had caught a rarity, and remarked to my companions that I believed I had got a _Dufourea_. I also hazarded the remark that it was "ten years since it had been taken." When I got home and looked up the former record it was ten years to a day. Now there are few places in England that have been better worked for the bee tribe than the Woking, Chobham, and Weybridge neighbourhood; it has been worked by experienced men who would see a difference {108} in the flight of an insect directly. The late Mr. F. Smith, in his day our leading authority, the Rev. F. D. Morice, than whom no one has probably worked the neighbourhood more thoroughly, Mr. T. R. Billups, Mr. E. B. Nevinson, and the late Mr. A. Beaumont, have all been over the ground again and again, and yet only these two _Dufoureas_! and these taken four miles apart. Here again is a problem which is very perplexing! What part in nature does this little rarity play? No doubt like everything else it has its duties, and its corner to fill, but beyond that one can suggest nothing.

Other bees are often exceedingly abundant in one season and very rare the next, or they will entirely desert a locality where they have been abundant, and move somewhere else--the occasional scarceness is due probably to continued wet weather, which often appears to kill the larvae. Cold winters seem to have no injurious effect, although at one time they were thought to determine the scarcity or otherwise of the bees of the following summer. It has, I think, been clearly shown that larvae can stand almost any amount of cold, although they succumb to {109} the effects of mildew produced by wet, but there is often no apparent reason why a well established colony should migrate to quite new pastures. Sometimes the proximity of new buildings or the digging up of ground may disturb them, but I know of colonies that have gone from where I knew them a comparatively few years ago, and where I can detect no change likely to have affected them. On the other hand there are colonies which one has known all one's life and which still go on as strongly or more strongly than ever--the case quoted under _Anthophora_, p. 63, shows what persistence there can be in some.

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{110}

ON BEES' WINGS

The Bees and the other stinging groups have four wings like all the _Hymenoptera_. These wings are almost always clear and transparent, at any rate amongst the British species, there being only one exception which I can call to mind in the female of the cuckoo of our large red-tailed humble-bee, which has the wings blackish; also they are never spotted, as in some flies. The hind or lower wings unite with the upper by a series of very beautiful hooks which extend along their upper margin and fix on to the posterior edge of the front wing, which is folded back on itself so as to receive them; in flight the two wings are united, but when at rest they separate; these hooks are beautiful objects under a microscope; their numbers vary; and in some cases this variation is useful in distinguishing closely allied species from one another. The hum of a bee is caused, to a great extent, by {111} the vibration of the wings, but it has been shown that a loud buzzing noise can be emitted by bees which have lost their wings; this proceeds from the spiracles or holes in the outer covering of the creature through which it breathes. It is therefore not always easy to say how much of the hum is caused by wing vibration and how much by the action of the spiracles. Some, in fact most, of our solitary bees are almost silent in flight, and their note can be heard only when large numbers are flying together; others have a very peculiar shrill hum, by which even the species can almost be recognized. In bright, hot, sunny weather their flight is more rapid and their note attains a higher pitch. The bees with the highest pitched hum with which I am acquainted are the two smaller species of _Anthophora_ and _Saropoda bimaculata_.

In early spring, when it is hot in the sunshine and cold when a cloud covers the sun, it is no unusual thing to see a bee drop to the ground. The cold seems to paralyze altogether their powers of flight. When at rest a bee folds its wings along the sides of its back, but only in the wasp tribe is there the arrangement for them to be {112} folded longitudinally. The shape of the wings varies very little, but the arrangement and number of their cells vary considerably. There are some very interesting genera in which the neuration of some of the cells is so slightly indicated that they are hardly visible, and can be seen only when the wing is held in certain lights; these faintly indicated cells are nearly always those towards the apex of the wing, the neuration of the basal part of the wing being as strong as in the other genera. There are a few moths in this country which very much resemble, both in the colour of their bodies and their clear wings, the wasp tribe, but they may be known by the brown band of scales at the apex of the wings and also by the absence of the narrow waist, which exists in all the stinging tribes. The only wingless forms which we know are to be found amongst the ants and the fossors, and as a rule are females, but in a few cases in the ants, and in some foreign species of the genus _Mutilla_, the male is apterous also.

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{113}

ON BREEDING ACULEATES, ETC.

Any one who wishes to study the life-histories of these insects, and has leisure to do so, can easily obtain various larvae by digging for them in suitable places. If, for instance, during the summer, bees, etc., have been noticed entering holes in a certain bank or sandy spot, their larvae or nymphs can be got in the autumn by digging down for about a foot in the direction of the holes, and if they be brought home and put into glass-top boxes they will generally emerge at their right time without giving any further trouble; it must, however, be remembered that the grubs are very soft and tender skinned, and it is better to avoid handling them if possible; they should be moved with a small soft camel-hair pencil, and it is well to put something soft at the bottom of the box so that if they fall in they will not be damaged. If the wood-boring {114} species are being collected, care must of course be taken in splitting the wood; most of these make a pupa case over themselves, and are in that respect easier to deal with. A label should be put in each box to show where the larvae, etc., were found. An old rotten stump of a tree will often produce a good number of species. Then there are the bramble-stem borers; these can be left in the stems. I have generally found it convenient, after arriving home, to split the stems down, to see if there are any living creatures in them, and, if there are, to close them up again, and, tie a little very fine net or gauze bag over the top of each stem; in this way one can find out exactly what insects come from what stem, and determine the cuckoos (if any) which belong to each. As the season advances towards May, it is well to give all the larvae, etc., an occasional glimpse of the sun; they should not be left in the sun long enough for them to get dried up too much, but the sun is a very important factor in tempting them to emerge; naked larvae and nymphs, in glass-top boxes, should be treated very carefully in this respect, as they are deprived of their {115} natural surroundings, in which the actual sunshine would never reach them--it would be better to place them in a sunny room, screened off from the actual rays of the sun, so that its warmth only would be felt. If they do not emerge the first year, it should not be taken for granted that they are dead, as very likely they will appear in the following spring. I have bred leaf-cutting bees several times with great success, and others I know have been successful with many species. The fear is to get them dried up too much; it is therefore not desirable to keep them in a very hot room. When first the insects emerge, their hairs are often more or less matted together, and they should be put in the sun in a larger box, so that they can crawl about and clean themselves; portions also of the skin in which they have been enveloped frequently adhere to them for some little time, but as a rule, unless the creature be too weak, these are very soon cleaned off. Breeding is a fascinating amusement, but it requires a great deal of attention when the emerging season begins, as the boxes want constant watching, or the insects will emerge unnoticed, and, if not given proper {116} air and sunshine, may die without cleaning themselves properly.

If it is desired to preserve the specimens, they should be killed either with cyanide of potassium, ether, or chloroform. If the first of these agents is used, a piece of about the size of a small hazel nut should be put at the bottom of a bottle (for collecting purposes, an ordinary "Coleoptera bottle", which can be obtained from any naturalist's shop, is the most convenient) and should be kept down by a wad of blotting paper, well pressed down upon it; this prevents the cyanide, as it liquifies, from wetting the hairs, etc., of the insects. Over this a piece of white paper should be placed; this will get stained at once when there is much damp, and should then be changed. The objections to cyanide are its very poisonous nature, and the stiffness which is caused by its use to the specimens killed by it, and also its tendency to turn yellow colours red. I always use it myself as I think it is preferable to the other insecticides, notwithstanding its demerits, but then I do not extend the legs and wings of my specimens, but simply leave them in whatever position they happen to {117} die. Ether is a very favourite method of killing with many; a few drops in a bottle with some paper in it is sufficient to last for some hours; it however soon evaporates in hot weather, and it is necessary to carry a small phial of it in one's pocket to replenish the supply when exhausted; this makes one smell of ether perpetually, which is more than I can stand. But the insects killed in this way are beautifully supple, and, for those who wish to set their captures as they would _Lepidoptera_, it is an excellent medium, i.e. if they don't mind its smell; it has also the benefit of not affecting colour. Chloroform acts much as ether does. When killed, I strongly recommend collectors to pin their specimens through the thorax with a very fine pin (those used for micro-lepidoptera are the best), and then to pin this through a narrow strip of card, mounted on a long stout pin; in this way the insect can be moved about by the strong pin, and the thorax of the insect itself is not destroyed, as it often is in the case of the smaller species by the use of thicker pins. The cards should be cut as small as possible; they need not be more than a quarter of an inch long. The insect {118} should be pinned at right angles to the long axis of the card, and the long pin should be inserted on the right-hand side of the insect so as not quite to touch it. In this way the insects look quite as neat as if they were pinned direct. Locality labels, etc., should be affixed to the long pin, and the insects should be stored in cabinets or boxes.

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{119}

ON COLOUR

There is but little tendency towards brilliant coloration amongst our native aculeates. No doubt our comparatively high latitude accounts for this to some extent, as also the fact that the aculeates do not, as a rule, elsewhere assume great brilliancy. Even in the tropics and other warm regions, where bright green, blue or coppery coloured species occur, they are comparatively few in number. In this country metallic colours are to be found in less than a dozen species, and in most of these it exists only as a tinge. Amongst our ants and wasps it does not exist at all, unless the slight bronziness of the typical form of _Formica fusca_ be so considered. The fossors can exhibit only a bluish tint in _Mutilla Europaea_ (pl. A, 4, 5), and a slight bronzy tinge in two of quite the smallest species, _Miscophus maritimus_ and the [male] of _Crabro albilabris_. The bees can do a little better; five species of _Halictus_ have a distinctly {120} bronzy head and thorax, and in three the bronzy colour extends to the abdomen; there is also another with a very dull green tinge on the thorax; besides these there is a little bright blue bee, _Ceratina_ (unfortunately a great rarity in this country) and two or three species of _Osmia_, showing more or less tendency to bronziness, and one which is distinctly bluish; but, considering our indigenous species number nearly 400, this is a very small, and compared with other countries I should think an abnormally small, proportion.

Species with bodies banded like a wasp's are much more abundant--no less than eighty of our native kinds having this style of coloration. The bands may be reduced to lateral spots, but such cases, I think, are only modifications of the banded scheme.

Black species with a more or less pronounced red band across the body number about seventy, and a general testaceous or yellowish colour occurs in a few ants, but not elsewhere among the British aculeates. Nearly all the rest are black or dark brown so far as the actual surface of the body is concerned; but amongst the bees {121} there is often a dense clothing of coloured hairs sometimes so dense that the surface of the body may be rendered invisible. These coloured hairs may be distributed into brilliant bands, as in the humble bees, or they may be uniformly black, as in some of their varieties and in the females of the spring species of _Anthophora_ (pl. D, 25), or entirely red as in _Andrena fulva_ (pl. B, 16), or black on the thorax and red on the abdomen as in _Osmia bicolor_ (pl. D, 28), or vice versa as in _Andrena thoracica_, etc., but the most usual condition is that where the hairs form more or less pale bands along the joints of the segments, either immediately above or below them or both; sometimes these bands are very obscurely indicated, and visible only in certain positions. At others they are vividly white; to a certain extent this banded condition recalls the waspy coloration. The hairs, however, of the bands are rarely yellow, but as a rule greyish or white, or of a grade of colour slightly paler than those of the disc. There are some rather interesting points which arise out of this rough analysis. Among the bees, all the species which have a waspy coloration are cuckoos, with only one exception (_Anthidium_) {122} (pl. D, 27), as are also nearly all those which have red bands. With the exception of the males of three species of _Halictus_, and both sexes of three or four species of _Andrena_, all the red-banded forms belong to the genus _Sphecodes_ (pl. B, 11), which is a cuckoo genus. The red coloration occurs chiefly on nearly naked surfaces; this is specially noticeable in those bees which have two varieties, such as _Andrena rosae_, one dull coloured and the other red-banded: in these cases the dull form is hairy and the red nearly naked. The greatest proportionate number of banded species occurs amongst the fossors, and these are seldom clothed with hairs to any extent. These bands seem to me probably to depend a good deal on retarded development. Dark and hairy bands, both as a rule, follow the joints of the segments, as stated above. I only say as a rule, as there are many where the banding does not follow this principle, but in far the larger majority the bands, whether of dark colour or hairs, are apical. As the segments overlap at the joints it is evident that their discs would tend to mature more rapidly than the overlapping bases and apices, {123} and the longer period spent in hardening and drying of the overlapping parts would favour the development of dark pigment and of hairs. Many species have the extreme apices of the segments pale, but with the apical integument so very thin, often looking nearly transparent and membranous, that its development would be very rapid. Again, in the case of red coloration, the red generally occurs on the discs of the segments, the apices and sides often being dark, and in cases where in one species both black and banded forms occur, with intermediate varieties, the last remnant of red colour is generally situated in the centre of the segment. By far the gayest effect is displayed by our humble bees, and, but for them and a few of the species of _Andrena_ and the wasp-coloured species, our aculeates would be a very sombre lot.

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{124}

THE DEVELOPMENT OF INSECTS FROM THE EGG

Although this and the following chapter may not be interesting to all my readers, I think it is only right to add some remarks on the structure and classification of insects, so that any one who wishes to follow up the subject may gather a few general ideas which may induce them to take up some technical and scientific work in which they will get fuller and more exact data on the difficulties which are involved in such simple questions as "What is an insect?" "How are the different orders of insects distinguished from each other?" "What is a species?" etc.

To realize the characters of an insect in its perfect or "imago" state, we may for the moment forget what often seems to be its most important features, and which are frequently its most extensive parts, viz. its limbs or {125} appendages; by limbs are meant its wings, legs, horns or antennae, jaws or mandibles, etc.: strip these all off, and we have a limbless trunk, which many would not recognize as belonging to an insect at all; still this limbless trunk possesses characters which assert its insect nature, as it may be known from other limbless trunks by being divided into three parts by two great transverse divisions; in most insects these are extremely well marked, and in all they have a very real existence. The parts thus divided off are known by the names of head, thorax, and abdomen. Anybody knows how easy it is to break off the head or body of a dried insect. Now the head or body breaks off at one of these divisions, and it is this partitioning of the body into three sections which makes one of the strongest characters in the definition of an insect. The three parts, thus divided off, each possesses special functions in the life of the creature. In the head are contained the principal organs of sense and brain; in the thorax, the organs of locomotion; and in the body those of digestion, reproduction, etc.

This division into three parts does not however {126} always hold good in the early stages of the insect's life, and we must remember that the creature commences life on leaving the egg, and not merely on its emergence from the chrysalis, so that we have to reckon with caterpillars, grubs and all sorts of curious immature forms in our conceptions of an insect.

These early stages do not as a rule interest the public much, but it is well to bear in mind that the "perfect insect" stage is reached by some insects along apparently a very different road from that travelled by others. Some leave the egg as caterpillars or grubs, and after various changes of skin become apparently lifeless chrysalids, from which they emerge as perfect insects. Others leave the egg as diminutive likenesses of their parents, and run or hop about much as they do, attaining the perfect insect stage simply by a series of changes of skin, without any definite quiescent or chrysalis condition.

The observation, therefore, which one often hears that insects never grow, has to be taken with caution; all insects grow in their early stages, but it is an obvious truth that insects do not {127} grow after they attain the imago or "perfect insect" condition. A small fly will never become a large fly, nor a small beetle a large beetle. This is only because we do not recognize their caterpillars or grubs as flies and beetles; but a grasshopper we know grows, because its early stages are of the same general form as the perfect insect, and we see the little ones hopping about in some places, and if we visit the same place later on we notice that they have grown, but as soon as they cast their last skin and obtain the free use of their wings, growth ceases, as it does in a fly or a beetle or in any other insect.