Graenicher—Andrenine Bees and Entomophilous Flora. 93 
With us the blossoming of the first catkins of our earliest 
species of willow, Salix discolor falls together with the appear¬ 
ance of our earliest species of Andrena, A. cockerelli, an oligo- 
tropic visitor of the willows. In a certain locality in the Menom¬ 
onee valley numerous specimens of Salix discolor occur, and 
among these a large specimen, bearing pistillate catkins opens 
its blossoms regularly in advance of all the other specimens. 
This particular plant was kept under observation in the early 
days of spring for 2 successive seasons, with the result, that 
on the first warm and bright day bringing out its blossoms the 
presence of the bee Andrena cockerelli in both sexes was noticed. 
This was the case on April 6th, .1902, and again on March 31st 
in the exceptionally early spring of 1903. I have never suc¬ 
ceeded in coming across a species of Andrena before our willow- 
blossoms appear, although two species of entomophilous plants, 
Erigenia bulbosa and Hepatica acuta open up their flowers ear¬ 
lier than this willow. As the willow-blossoms become more 
abundant additional species of Andrena arrive on the scene, so 
that at the end of the third week in April 8 species are on the 
wing, 4 of which are oligotropic, depending for pollen on the wil¬ 
lows exclusively, although they also visit other flowers for nectar. 
These facts point to the importance of the willows in the econ¬ 
omy of our first arrivals among the Andrenine bees. As the 
season advances several other flowers attractive to insects open 
up, among them being Claytonia Virginica which usually ap¬ 
pears towards the end of April, and also has an oligotropic 
visitor Andrena erigeniae. At the beginning of May 13 species 
of Andrena are present, and this number is gradually increased 
during the month until a maximum with 24 species is reached 
in the latter part of May, and lasting throughout the first week 
in June. This is the maximum of our spring-group of Andre- 
ninae, and it corresponds with the blooming period of a great 
variety of flowers, representing different families. Seven of 
these bees are oligotropic, two of which collect pollen from the 
late species of willows, one from Fragaria Virginiana, one from 
Hydrophyllum Virginicum, one from Geranium maculatum, and 
the two remaining ones from umbelliferous plants. Two species 
of Umbelliferae Thaspium Irifolialum aureum and Taenidia in- 
