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.