These insects are not distinguished for any elaborate economy. Varying in the species, some prefer vertical banks, others sloping undulations, and again others horizontal flat ground or hard down-trodden pathways. Some burrow singly, and others are gregarious, collected in great numbers upon one spot. They are, perhaps, the most inartificial burrowers of all the bees. Their tunnels vary from five to nine or ten inches in depth, and in some species they are formed with other small tunnels slanting off from the main cylinder. The sides and bottom are merely smoothed, without either drapery or polish. The little cells thus formed are then supplied with the usual mixture of pollen and honey kneaded together, which in the larger species forms a mass of about the size of a moderate red currant, its instinct teaching it the quantity necessary for the nurture of the young which shall proceed from the egg that it then deposits upon this collected mass of food. The aperture of each little tunnel is closed with particles of the earth or sand wherein the insect burrows, and it proceeds to the elaboration of another receptacle for a fresh brood until its stock of eggs becomes exhausted. Some species have two broods hatched in the year, especially the earlier ones,—for several present themselves with the earliest flowers,—but others are restricted to but one. The quantity of pollen they collect is considerable, and in fact they are supplied with an apparatus additional to what is furnished to any of the other genera in a curled rather long lock of hair that emanates from the posterior trochanters. This, with the fringes that edge the lower portion and sides of the metathorax, as well as the usual apparatus upon the posterior legs, enables the insect to carry in each flight home a comparatively large quantity of pollen, but perhaps scarcely enough at once for the nurture of one young one, and it therefore repeats the same operation until sufficient is accumulated.
The exact period occupied by their transformations is not strictly known; it will, of course, vary in the species, as also in those in which two broods succeed each other in the year, but the larva rapidly consumes its store and then undergoes its transformation. It does not spin a cocoon, but in its pupa state it is covered all over with a thin pellicle, which adheres closely to all the distinct parts of the body. It is not known how this is formed; perhaps it is a membrane which transudes in a secretion through the skin of the larva, or it may be this itself converted to its new use, which seems to be for the protection of all the parts of the now transmuting imago, until these in due course shall have acquired their proper consistency.
These insects in their perfect state vary very considerably in size, both individually and specifically, the former depending upon both the quantity and quality of the food stored up, for the pollen of different plants varies possibly in its amount of nutriment, else why should we observe so marked a difference in the sizes of individuals whose parent instinct would prompt to furnish them with an uniform and equal supply. The differences of specific appearance is often very considerable in long genera, and perhaps in no genus is it more conspicuously so than in Andrena, for here we have some wholly covered with dense hair, and others almost glabrous; others again with the thorax only pubescent; some are black, some white, some fulvous, or golden tinted, and some red; some we find banded with decumbent down, and others with merely lateral spots of this close hair, but the most prevalent colour is brown, which will sometimes by immaturity take a fulvous or reddish hue. In many males we see excentrically large transversely square heads broader than the thorax, which also have widely spreading forcipate mandibles, with often a downward projecting spine at their base beneath; and it is chiefly these extravagantly formed males which are most dissimilar to their own partners that the result of observation alone confirms their specific identity. In other cases the males are so like their females that a mere neophyte would unite them. In many males the clypeus and labrum are white, which also occurs in some females; for instance, in A. labialis, but this peculiarity is found more rarely in this sex. The species are much exposed to the restricting influences of several parasites, whose parasitism is of a varying character, but the term should properly be applied only to the bees which deposit their eggs in their nests, and whose young, like that of the cuckoo among the birds, thrives at the expense of the young of the sitos by consuming its food, and thus starving it. These parasites consist of many of the species of Nomada, very pretty and gay insects, but in every case totally unlike the bee whose nest they usurp. Several of the species of these Nomadæ are not limited to any particular species of Andrena, but infest several indifferently, whereas others have no wider range in their spoliation than one single species, to which they always confine themselves. In my observations under the genus Nomada I shall notify those which they assail amongst the Andrenæ, as well as the other genera which they also infest.
The others which attack them are more properly positive enemies than parasites, for they prey upon the bees themselves, or, as in the case of the remarkable genus Stylops, render the bee abortive by consuming its viscera and ovaries. I have spoken of these insects in the chapter upon parasites, to which I must refer, but I may here add that the female is apterous, and never quits the body of the bee. Much mystery attaches to their history in which their impregnation is involved, for the male, immediately upon undergoing its change into the imago, escapes through the dorsal plates of the abdomen of the bee wherein it was bred and takes flight. In localities where they occur they may be usually taken on the wing in the month of May. The female would seem to be viviparous, and produces extraordinary multitudes at one birth, extending to hundreds. Being born as larvæ within the body of the bee they seek to escape from their confinement, and find the opportunity in the suture which separates the mesothorax from the metathorax. Their extreme minuteness admits of their passing through the very constricted tube which connects the abdomen with the thorax. Having now escaped into the air they alight upon the flowers which the bee frequents, and thence they affix themselves to other bees which may visit these plants, and thus perpetuate the activity of the function it is their instinct to fulfil. That many may be lost there can be no question; but Nature is very prodigal of life, for by life it endows life, and thus its activity is enlarged to a wider circle. Although the matured Stylops has preyed upon all the internal organs of the bee its attack is not immediately fatal, although the life of the creature may be thus considerably abridged, but it seems to live sufficiently long afterwards to disseminate the distribution of the Stylops. A small blackish Pediculus, which Mr. Kirby called Pediculus Melittæ, is found also both upon the flowers the bees frequent and also upon the bees themselves, especially the pubescent ones; but this insect is not limited to the genus Andrena, as I shall have occasion to notice. The flower I have chiefly found them upon is the Dandelion (Leontodon). Their peculiar economy and connection with the bees is unknown; it may be merely an accidental and temporary attachment, but they even accompany them to their burrows.
Another and more curious case of attack upon the young of the Andrena, is instanced in the reputed parasitism of the Coleopterous genus Meloë. The perfect insect is a large apterous, fleshy, heteromerous beetle, ten times as big as the bee. Its vermicle, having issued from the egg, has the appearance of a very small pediculus, of an orange colour. They are often seen upon flowers, and, like the former pediculus, attach themselves to such suitable Andrena as may happen to visit the flowers they are upon; and, it is said, that they are thus conveyed by the bee to its domicile, and there feed to maturity upon the larva of the bee. I have no faith in the correctness of this statement, for it is not credible that so small a creature as the larva of an Andrena could fully feed the larva of so large a beetle. Observation has not satisfactorily confirmed it, and the connection may be, as in the former case, merely accidental.
Although, perhaps, not a strictly scientific course, it is certainly a matter of convenience in very long genera to break them up into divisions, framed upon external characters, readily perceptible, and, by which means, the species sought for may be more readily found. This I have done in the preceding list of the species, and which are based upon very prominent features. A slight divarication from the typical neuration of the wing is observed in some species, but it is not of a sufficiently marked character to afford a divisional separation, and even much less a subgeneric one. I have therefore passed it unnoticed. The commencing entomologist will often find considerable difficulty at first in determining the species of this genus, for so much depends upon condition; and where the colour of the pubescence is the chief characteristic, a very little exposure to the atmosphere much alters their physiognomy, but time, patience, and perseverance will ripen the novice into an adept. The connection of the males with the females, from their ordinarily great dissimilarity, was only to be accomplished by positive observation, but now that this, in the majority of cases, is effected, good descriptions facilitate their discrimination.
The most conspicuous species are the Hattorfiana and the Rosæ for size and colour; the Schrankella is also a very pretty species; and perhaps the commonest of all the cingulata is the prettiest of all, with its yellow nose and red abdomen; in the next section we may point out the longipes as being a very elegant insect,[[3]] as are also the chrysosceles and the helvola. In this section we find those most subject to the attacks of the Stylops, for instance the labialis, convexiuscula, picicornis, Afzeliella, nigro-ænea, Trimmerana, Gwynana, etc. The whole of the third and fourth sections are splendid insects, especially the fulva in the last. The comparative rarity of some results chiefly from an exceedingly local habitat. Many of the species may be found everywhere where insects can be collected, consequently, all over the United Kingdom. In all the three seasons of the year, which prompt animal life, some of the species may be collected, and the flowers they chiefly prefer are the catkins, especially of the sallow, the early flowering-fruits, the hedge-row blossoms, the heath, the broom, the dandelion, chickweed, and very many others.
[3]. This insect was first captured by me, and with this, my manuscript name, attached to it, it was distributed to entomologists with an unsparing hand. The ordinary courtesy of the science has been, for the describer, when not the capturer, to adopt and circulate the original authority, and not to appropriate it. Similar buccaneering has been practised with poor Bainbridge’s Osmia pilicornis, to which he had attached this manuscript name, he being the first to introduce it, having caught it at Birchwood.
Genus 5. Cilissa, Leach.