discolor) are great favorites of vernal species of Andrena, whence Smith calls them "harbingers of spring." The pussy-willows bloom in northern New England during the latter part of April, and their bright yellow aments are very pleasing objects in the cold gray landscape. They are very attractive to a varied company of insects, as honey-bees, bumblebees, flies, butterflies and beetles. It is a busy scene and one which the naturalist can never tire of watching; but it is not one of unmixed happiness, for little tragedies take place before our eyes. Among those which come to sip the nectar are little dance-flies (Empididæ), and not infrequently they are seized and carried away bodily by black robber ants, which roam everywhere. Honey-bees and many species of Andrena come in great numbers to procure pollen for brood-rearing. A part of the Andrenid bees gather only a portion of the pollen they require from the willows and the balance from the maples, plums, cornels and Viburnums; but there are four species (A. illinoiensis, A. mariæ, A. erythrogaster and A. moesta), which get their whole supply from this genus of plants. Of the autumnal flying species of Andrena there are five (A. canadensis, A. nubecula, A. solidaginis, A. hirticincta and A. asteris), which I have collected only on the flowers of the Compositæ, or aster family; and four of these bees confine their visits very largely to the golden-rods. In both Salix and Solidago the inflorescence offers an ample supply of nectar and pollen and there is little temptation for Andrenid bees to go elsewhere, when their time of flight coincides with the period of blooming of these two genera.
But in other localities Andrena erigeniæ is reported to be a monotropic visitor of the spring beauty (Claytonia virginica), Andrena violæ of the violet (Viola cucullata), Andrena geranii maculata of the wild geranium (Geranium maculatum), Andrena fragariana of the strawberry (Fragaria virginica) and Andrena parnassiæ of Parnassia caroliniana. It is not so easy to explain the behavior of these latter bees. It seems very remarkable that they should restrict their visits so closely to the flowers mentioned.
Macropis ciliata, or the loosestrife bee, usually gets its pollen from the flowers of the common loosestrife (Lysimachia vulgaris); while many species of Panurginus are taken only on the inflorescence of the Compositæ.
But this habit of visiting only one kind of flower is perhaps better illustrated by Perdita than by any other genus of bees. Only one species of Perdita is found in Maine; but in the western states some 90 species occur, of which about forty live in the arid regions of New Mexico. In Maine Perdita octomaculata is found almost exclusively on the panicles of Solidago juncea, the earliest blooming of the golden-rods; and I have never met with it on any other species except in one instance. In New Mexico two species of Perdita are found on the willows, Perdita zebrata visits only Cleome serrulata, Perdita crotonis