This genus is named from the presence of a little horn between its antennæ, κερατίνη, a horn. Some foreign entomologists, especially Latreille and Le Pelletier de St. Fargeau, have considered it to be parasitical, but that it is not so we have the authority of the Marquis Spinola, of Genoa, confirmed by the testimony of Mr. Thwaites, a very accurate observer, in the vicinity of Bristol, where the insect is not at all uncommon, although extremely rare in most other parts, and consequently usually a desideratum to cabinets, from its great beauty both of form and colour, notwithstanding that it is so very small in size. It has also been found in other localities, as at Birchwood, where the late Mr. Bambridge used to take it, and as near London as Charlton, at both which places I have no doubt it might frequently be found were it carefully looked for, but the practised entomological eye is often wanting to detect an insect unless it be conspicuously present. Its usual nidus is a bramble or briar stick, from which it excavates the pith, and this it has been frequently observed doing, and both sexes have been repeatedly bred from such sticks. We have no notice of any peculiarity in its mode of forming its cells, which may resemble that of such wood-boring genera as Chelostoma and Heriades, although its structure would intimate a closer affinity to the habits of the exotic genus Xylocopa; nor is there extant any account of the process or time occupied in the development of its young. Spinola’s notion, from not seeing the sufficiency of the hair upon the posterior tibiæ for the purpose, assumed that the pollen was conveyed home on the forehead and between the antennæ, he having caught an insect with some pollen accidentally incrusted there in the insect’s honey-seeking excursion. The hair upon these legs is very sparse, it is true, but then it is very long, and the quantity of pollen required for the nurture of the larva is evidently small, from its having been observed that the store upon which the egg is deposited is semi-liquid, thus preponderating in the admixture of honey.
That it has not been caught laden with pollen upon its legs has no weight against the fact of its non-parasitism, for it is not always that the excursions of bees are made for the purpose of collecting pollen. Honey is as necessary to their economy—and in this case perhaps more so—as pollen, and the only way to determine the fact of its carrying pollen, corroboratively, would be when knowing that one of these bees has visited a bramble stick—its presumptive nidus,—to watch the stick very patiently for the insect’s return from every journey until it came back laden; the presence of pollen upon its legs would surely be indicated by the difference of its colour from the ordinary dark hue of the little labourer.
We have already noticed bees with metallic hues among the Halicti, and there are slight indications of it in some of the Andrenæ, for instance, in the A. cinerea and the A. nigro-ænea, etc., but in none hitherto so absolutely is it exhibited as in this genus. The prevalent colour of the bees, that is to say, the ground colour of the integument, and not the fleeting one of the pubescence, is black or brown, but here we have a positive metallic tinge, which we shall again come across in many shades and hues in the genus Osmia.
A second species of the genus was brought from Devonshire by Dr. Leach, and is in the collection of the British Museum, but no other specimens of the same species have since been found.
The only flower which it has been noticed that they frequent is the Viper’s Bugloss (Echium vulgare).
Subsection 2. Nudipedes (naked-legged cuckoo-bees).
a. With three submarginal cells to the wings.
Genus 14. Nomada, Fabricius.