There is very great dissimilarity in the habits of the various species, whence no single characteristic will embrace them, nor is there any distinctive feature whereby the genus might bear subdivision, either from habits or habit, as will be collected from the following cursory survey of their special natural history.
Thus the first species, the O. leucomelana, named so from the white decumbent down which edges the black segments of the abdomen, extracts the pith from bramble sticks, and its cells are formed and closed with a composition made of triturated wood or leaves. The cylinders it forms are usually about five inches deep, and within this it constructs about the same number of cells proportionate to the small size of the insect. These are midsummer insects, coming forth in June and July; they are very local, but seem to abound in the vicinity of Bristol, whence Mr. Thwaites formerly sent me specimens. A very few days serve for the hatching of the larva, which spins a slight silken cocoon, and in this dormitory it reposes until its season again comes round. Under the influence of the following first genial spring weather, the larva is transmuted into the pupa, and the active little imago comes forth upon the settlement of our variable spring, in the merry days of June, and thus is perpetuated the circle of its existence, but which is sometimes abridged by its special parasite, the pretty little Stelis octomaculata. Many of the species in the males are distinguished by a peculiar armature of the apex of the abdomen; the second being named by Kirby from the circumstance. A very remarkable singularity distinguishes the males of the third species, in the fringe of short hair that runs along the flagellum of its antennæ. This, I believe, was first noticed by the late Mr. Bainbridge, a very active practical entomologist, who took the insect at Darenth or Birchwood, and distributed specimens with this manuscript name attached, which has since been appropriated by another entomologist to whom the science was wholly unknown at that time, but as it is scarcely consistent with scientific courtesy to adopt such a course, and as the MS. names of Linnæus and Kirby have been retained, where it was authorized by their being attached to undescribed species, I have restored to Mr. Bainbridge his just rights, and have claimed the same for myself, in the case of Andrena longipes, and which many cabinets must still possess with my name attached, in my own writing, unless their possessors have chosen to adopt the illegitimate parentage; for the entomologists of my own standing well know that I always freely distributed specimens to all who desired them of the many very desirable insects which I have captured in the course of my entomological career. The fourth and the ninth species, the O. bicolor and O. aurulenta, have very much the same habits, both usually burrowing in sandbanks, sometimes however in wood, in which case the perforation, contrary to the mode of wood-drilling bees, is made upwards, a sagacity or instinct which saves it much trouble, for the particles as they are removed by the mandibles are passed beneath the insect, and their own gravity carries them downwards, and thus the insect saves itself the labour of conveying them out as they accumulate in inconvenient quantities. The cells in this case are placed end to end. When they burrow in the earth, the latter species often associate gregariously in large numbers, and if they select a cavity, instead of tunnelling it themselves, and it be too large to take one cell upon the others, they form them side by side, and thus fill the space. This is the case when they adopt snail-shells as the receptacle for their incunabula, and this is done by both these species, and the shells they select are the empty ones of Helix nemoralis, hortensis, and adspersa. The capacity of the latter shell being much greater than that of the others, and too wide for a single succession, she fills the interval by placing them side by side, and with the increase of the whorl of the shell towards its orifice she places them across the space, and thus completes her task. In the former shells, the cavity at first admits of the succession of but one upon the other, but with its enlargement she places them side by side, and this repeated fills the hollow. Its aperture is then closed with earth and pebbles or sticks agglutinated together, as described at the commencement. The O. fulviventris burrows in wood, and upon this species the Stelis phæoptera is parasitical; and that very pretty but extremely common species the O. ænea, in which the male is of a rich bronzy tint, and the female of a beautiful blue, verging sometimes to nearly black, burrows also in wood, although sometimes it capriciously selects old walls or chalk-cliffs, and is subject to the incursions of the same parasite. Perhaps the most extraordinary species is the O. parietina, figured and named by Curtis, and which he first found at Ambleside; it has since been found in the Grampians very considerably above the level of the sea, and it is thus essentially a northern species both from altitude and locality. It would appear that this species selects some flat stone of about a foot in surface, lying upon the ground over a hollow spot. Such a specimen, sent to the British Museum, had attached to its under side two hundred and thirty cocoons, indicative of a considerable colony, or perhaps the accumulation of successive years, as one-third of these cocoons were empty of tenants. These, in their new depository, continued developing themselves in the perfect state between March and June, males appearing first. When the transformations of the season ceased, five-and-thirty were still left to present themselves another year, and the following spring these were developed; thus, including those which had already escaped when the stone and its treasure was secured, three successive seasons were occupied in their transmutations. It may be a species that requires three years for its metamorphosis, and the whole deposit of cocoons may have been the result of three years’ accumulative structure, the vital activity of their northern life being perhaps more sluggish than in species frequenting the south. The last species the O. rufa, that in which the female is remarkable for its inverted horns, which must be for some use in its economy, is perhaps the most common of all. I have found it in abundance upon old walls with a sunny aspect at Erith, and throughout the pleasant Crays of Kent. It is indifferent as to the choice of its domicile, selecting either walls, where I have chiefly found them, sandbanks, or the decaying stumps of pollard-willows. Its processes are similar to those of some of the earlier described, but its larva is longer in full feeding, which, when it has consumed all its provender spins a tough cocoon of brown silk, wherein it undergoes its changes; some, depending much upon locality, pass into pupæ in the autumn, others hibernate as larvæ which are subject to destruction from the attacks of the Chalcideous insect, Monodontomerus dentipes, previously noticed under Anthophora. Some of the Chrysididæ also infest several of the species of this genus, and I have no doubt that Stelis aterrima is parasitical upon one of them, although it has not been recorded. The various species frequent many flowers, especially those abundant in the locality they inhabit, but the O. pilicornis chiefly affects the common Bugle (Ajuga reptans), and they much frequent composite flowers, especially the species of the genus Hieracium.
Section 2. Cenobites (dwellers in community).
Subsection 1. Spurred.
† Parasitical.
Genus 25. Apathus, Newman.
([Plate XIV.] figs. 1 and 2.)
Apis ** e 2 partly, Kirby.—Psithyrus, St. Fargeau.
Gen. Char.: Body subhirsute. Head subglobose; vertex broad, glabrous, with a deeply impressed cross upon its summit, in the centre of which the ocelli are placed in an almost straight line and contiguously; antennæ short, filiform, geniculated, the scape slightly curved, the basal joint of the flagellum subglobose, its second joint as long as the terminal one and subclavate, the rest short, subequal, but gradually increasing in length to the terminal one, which is laterally compressed; the face flat; clypeus transversely lunate but straight in front; labrum lunulate, tuberculated laterally; mandibles broad and obscurely bidentate; cibarial apparatus moderate; tongue twice the length of the labium, tapering from base to apex, where it terminates in a small knob, and is clothed with short hair; paraglossæ obsolete; labial palpi as long as the tongue, the two first joints long and membranous and tapering to the apex of the second, which is acute, and about one-fourth the length of the first, it has the two very short, subclavate, terminal joints, which are conterminous, and articulated just before its acute apex; maxillæ subhastate and acuminate; maxillary palpi very short, linear, and equal. Thorax globose, pubescent, concealing its divisions; metathorax truncated; wings with three submarginal cells nearly equal, or the third the largest, the second receiving the first recurrent nervure at about one-third its length, and the second is received by the third submarginal cell near its extremity; legs setose; the posterior tibiæ convex, very slightly enlarging from base to apex, rounded at the extremity externally, and unfurnished with means to convey pollen; posterior plantæ oblong, narrowly equal, and not auriculated; claws bifid. Abdomen ovate, convex above, deflecting toward its extremity, and subglabrous on the disk, the terminal dorsal segment triangular, and its ventral plate straight at its apex with the lateral angles reflected, making it concave beneath and subcarinated longitudinally in the centre, or also triangular and the sides of the prominent angle deflected.