3. marginata, Linn., ♂ ♀. 3-4 lines.
4. Daviesiana, Kirby, ♂ ♀. 3½-4½ lines.
([Plate I.] fig. 1 ♂ ♀.)
GENERAL OBSERVATIONS.
This genus is named from κολλήτης, one that plasters, in allusion to the habits of the insects, which will be described below. The female insects themselves have, at the first glance, very much the appearance of the working honey-bee, but they are considerably smaller, and, upon a very slight inspection, they are found to be exceedingly distinct. The respective males of the species are conspicuously smaller than their females, but their specific characteristics are very much alike, and there is some difficulty in separating and determining the species. One strong peculiarity, marking all of them, is that the segments of the abdomen are banded with decumbent, hoary or whitish down, in both sexes, and the determination of the species lies chiefly in the variations of these bands, and in the almost entire absence or conspicuous presence of minute punctures covering the segments. The females are very active collectors of pollen, and return from their excursions to obtain it, very heavily laden to their nests. I am not sure that all the species are not gregarious, to use this term in an acceptation somewhat different from its usual application, for here, and whenever used in entomology, it is meant to signify that they burrow collectively in large communities, forming what is called their metropolis, although each bores its independent and separate tube, wherein to deposit its store of eggs. The males, neither in these insects nor throughout the whole family of the bees, participate at all in the labours required for the preservation and nurture of the progeny, a duty that wholly devolves upon the maternal solicitude of the female,—these males having fulfilled their mission, which is not perhaps restricted to their sexual instinct, but may also be conducive to the grand operation of the family in the economy of nature, viz. the fertilization of the flowering plants, flit from blossom to blossom, and thus convey about the impregnating dust. They may also be often seen basking in the sunshine upon the leaves of shrubs, and thence they become lost or dispersed or the prey of their many enemies,—birds or insects, which are always on the alert in search of ravin.
The aspect selected by the females for their burrows, varies according to the species. Some choose a northern, and others a southern aspect; thus, the C. succincta seems to prefer the former, and the C. fodiens the latter, as does also the C. Daviesana; and where they burrow they congregate in enormous multitudes. The mortar interstices of an old wall, or a vertical sand-rock, which, from exposure, is sufficiently softened for their purpose, are equally agreeable to them; nor have they any objection to clay banks.
In these localities each individual perforates a cylindrical cavity, slightly larger than itself, and which it excavates to a depth of from eight to ten inches, or even sometimes less. Now comes into operation the use of the peculiarly-formed tongue with which nature has furnished them, and described above in the generic character. These cells are occupied by a succession of six, or eight, or even sometimes no more than two, three, or four cartridge- or thimble-like cases, in each of which is deposited a single egg with a sufficiency, taught the creature by its instinct, of a mingled paste of honey and pollen, for the full nurture and development of the vermicle that will proceed from the egg upon its being hatched, and wherein this larva, having consumed its provender, becomes transformed into the pupa, and by the continuance of nature’s mysterious operations, it speedily changes into the perfect insect. But the beauty with which these little cells are formed transcends conception. Each consists of a succession of layers of a membrane more delicate than the thinnest goldbeater’s skin, and more lustrous than the most beautiful satin. In glitter it most resembles the trail left by the snail, and is evidently, from all experiments made, a secretion of the insect elaborated from some special food it consumes, and by means of its bilobated tongue, which it uses as a trowel, it plasters with it the sides and the bottom of the tube it has excavated to the extent necessary for one division. As this secretion dries rapidly to a membrane it is succeeded by others, to the number of three or four, which may be separated from each other by careful manipulation. It then stores this cell, deposits the egg, and proceeds to close it with a covercle of double the number of membranes with which the sides are furnished, and continues with another in a similar manner, until it has completed sufficient to fill the tubular cavity, which, after closing the last case similarly to the rest, it stops up the orifice with grains of sand or earth. The food stored up is subject to fermentation, but this does not appear to be prejudicial to the larva, which first consumes the liquid portion of the store and then drills into the centre of the more solid part, and continues enlarging this little cylinder until increasing in growth by its consumption, it itself fills the cavity, and thus supplies the lateral stay or prop which, by means of the stored provender, was previously prevented from falling in. It has not been ascertained what number of eggs each insect lays, or whether it bores more than one tube, but it is presumable that it may do so, and possibly thus, from the numbers annually produced, for there are two broods in the year, colonies are thrown off which gradually form another metropolis somewhere in the vicinity, although the majority continue to occupy the old habitat from year to year. But the number of these insects is kept within due limits by the individual abundance of the parasites that infest them, and by the unsparing and unflinching attacks of earwigs, which consume all before them,—perfect insect, larva, and provender. The two most conspicuous parasites they have, are the beautiful little bee, Epeolus variegatus, the young of which is sustained, as in all bee-parasitism, by consuming the food stored for the sustenance of the young of the Colletes; and the other is the little dipterous Miltogramma punctata, whose larva, evolved from the egg deposited in the cell, feeds upon the larva of the Colletes, or possibly upon that of the Epeolus, which otherwise would seem to have no check to its fertility, excepting that it may be subdued by the Forficulæ.
These insects are to be found during the spring and summer months, and throughout the southern counties, although some species are extremely local. Some occur also in the north of England and in Ireland. I am not prepared to say what flowers they prefer, for I have never captured them on flowers, but they have been found frequenting the Ragwort, and Curtis took a species at Parley Heath, in Hampshire, on the Bluebell (Campanula glomerata). They form a remarkable instance of an artisan bee, but so only in its habits, amongst the Andrenides.
Two submarginal cells to the wings.