19. morio, Kirby, ♂ ♀. 2-2½ lines.
GENERAL OBSERVATIONS.
This genus was named by Latreille from ἁλίξω, to crowd, or collect together, from the fact of their nidificating in numbers on the same spot.
The females closely resemble in form those of the genus Andrena, but the males are very unlike both those of that genus and their own females, for they all have long cylindrical bodies and very long antennæ, much longer relatively than those of the former genus. Although none of the species approach in size the larger ones of the preceding genus, their extremes of specific size are as distant apart as they are in that genus, the smallest being extremely minute. Some of even the commoner species are very pretty when in fine condition, and several of them have a rich metallic green or blue tint, and in the majority the wings are iridescent with the brightest and gayest colours of the rainbow. The numbers in which they associate together upon the same spot varies considerably, and a very few indeed burrow solitarily and apart from their congeners. In burrowing they form a tunnel which branches off to several cells, the excavations being as inartificial as are those of Andrena. Walkenaer tells us in his memoir upon the genus Halictus, that they line their cells with a kind of glaze, that they burrow in horizontal surfaces to a depth of about five inches, and which they polish very smoothly previous to covering it with their viscous secretion, and that the cells are all oval, the largest end being at the bottom. He says also that they burrow solely during the night, especially when the moon is shining, when it is difficult to walk without treading upon them; so numerous are they, indeed, that they look like a cloud floating close to the surface of the ground. Although burrowing thus at night, it is only during the day that they supply their nests with their provision of pollen and lay their eggs. Each of their cells is furnished with a small ball of pollen, varying in size with the species, but which never entirely fills the cell, and is affixed intermediately between both extremities, and upon the mass contained in each cell they deposit their small egg, which is placed at the extremity of the lump of pollen most distant from the entrance. The larva is hatched in about ten days, when it changes into the pupa. Some doubt attaches as to the length of time that the pupa remains before its transformation into the imago, and also as to the period at which this takes place. A peculiarity attends the appearance of the larger species. Some are very early spring insects, among which is the Halictus rubicundus; this I have seen in abundance on the first fine spring days collecting its stores on the flowers of the chickweed. It is then in the very finest condition, and it is really a very beautiful although a very common insect, having a richly golden fulvous pubescence on the thorax, an intensely black and glabrous abdomen, the apex of which is fringed with golden hair. No males are now to be found at all. Yet it is only some species, and these the larger ones, which are subject to this peculiarity, for the smaller ones I have found burrowing during the summer months in vertical or sloping banks with a sunny aspect, whilst the males were hovering about both in the vicinity and close by, sometimes either playing or fighting on the wing with the very small Nomadæ, which infest these species parasitically, whilst their females were sedulously pursuing their vocation. Gradually these joyous spring insects lose their gayness and their brilliancy, as do those which have followed in succession of development with the growing year, and they become senile and faded and are lost as they have progressively fulfilled their function. By this time the ragwort is in bloom, and the thistle displays its pinky blossoms; now the males are to be found numerously exhibiting themselves upon these flowers, and also another equally fresh brood to those of the spring and early summer, of females. My friend the late Mr. Pickering, who was in the early days of the present Entomological Society, when it held its meetings in Old Bond Street, its honorary curator, and who was then and always, even when less leisure was afforded him from professional duties, a most assiduous and diligent observer of the habits of insects, propounded his theory, both in conversation and before the meetings of the Society, although he never drew up a paper upon the subject, that these females were then impregnated, upon which they retired to a hibernaculum, and there remained until the breath of a new spring brought them forth in all the beauty of their gay attire, and that it was from their broods deposited thus in the spring and early summer, that the autumnal insects were developed. This theory is both plausible and possible, and I have no doubt that it is the correct one; and thus is explained the total absence of males at the time of the appearance of the females in the foremost portions of the year; this habit we shall find also in the Bombi.
The flowers they delight in, besides those previously named, are among others the ribwort plantain, and the bramble, as well as the Umbelliferæ and the flowers of the broom. The females possess two remarkable distinctions of structure not found in any of the other bees, which consist in an articulated appendage in the centre of the front margin of the labrum, and a vertical cleft in the terminal segment of the abdomen, both of which will necessarily have their uses in the economy of the insect, although what these may be has not been discovered.
They, like Andrena, are exposed to parasites and enemies. The smaller species of Nomada infest their smaller kinds, and St. Fargeau tells us that the Sphecodes are also parasitical upon them. The smallest of the genus, which is indeed an exceedingly minute insect, is subject to a very minute strepsipterous destroyer; whether this be a genuine Stylops I am not aware, but the supporting insect being so minute, in fact the smallest of our bees, how small must be the enemy bred within it! Another genus of this order has been found by Mr. Dale upon them, and which is figured as the genus Elenchus in Curtis’s ‘British Entomology.’ The smaller species are also attacked, upon their return home laden, by spiders and ants. Chryses and Hedychra are bred at their expense, and some of the Ichneumons attack them, as well as the fossorial Hymenoptera of the genera Cerceris, Crabro, and Philanthus, and these latter carry them off bodily to furnish their own nests with pabulum. Several of the species exhale a rich balmy odour, and, like all the Andrenidæ, they are silent on the wing, and their sting is innocuous and not painful. The males are very eager in their amours, and are not easily repulsed.
Some of the species vary slightly in the neuration of the wings, and this being a rather numerous genus, although not nearly approaching the extent of Andrena, it has been proposed to make use of it for its division, but I think this is scarcely required, it not being sufficiently abundant to cause any inconvenience, the species being so distinctly marked in their specific differences by the aid of the metallic brilliancy of several of them. I have therefore arranged the species in the above list in connective order without intermission, and have placed in juxtaposition those species which appear the closest in affinity.
b. With two submarginal cells to the wings.
Genus 7. Macropis, Panzer.