83 
Salix Cordata. Muhl . 
Salix Humilis, Marsh 
Three Early Species 
Early Species 
Salix Discolor. Muhl . 
Several species of Syrphidae are in attendance on the willow- 
tiowers most of the time in pleasant weather, and this is especially 
true of two very common species — Bristol is diinidiatns, Wied. and 
Hclophilus siinilis, Macq., which are occasionally so numerous on 
the flowers that they surpass the rest of the visitors, as far as the 
number of individuals is concerned. On April 23d, 1897, I saw 
plants of Salix discolor, growing near the city limits in Bay View, 
literally swarming with flies, belonging to these two species of 
Syrphidae. Although the Syrphidae take such a prominent part in 
the pollination of the willow-flowers, yet there are no close mutual 
relations existing l^etween these flies and the willows, as we have 
seen to exist between these plants and the Andrenidae. 
Having considered the more important groups of visitors of 
Salix discolor, it remains for us to turn our attention to the other 
visitors on the list. The only wasp observed on the flowers is a 
female of our social wasp, Polistcs pallipcs, Lep. ; none of our 
other species of wasps appear so early in the season, the solitary 
wasps notably coming out much later. The remaining hymenop- 
terous insects of the list are made up of seven parasitic Hymenop- 
tera, chiefly Ichneumonidae and five Tenthredinidae (saw-flies). 
The visitors Ijelonging to these families are of little importance, 
compared with the other Hymenoptera, and are only occasionally 
taken on the flowers. 
Among the flies we have in Myopa pilosa, Will., a single 
species of the Conopidae, a family ranking as high as the 
Syrphidae, as regards the adaptation of its members to flowers, 
hwi having comparatively few representatives in our region. 
Of the three species of Tachinidae, we have already come 
across two (Gonia capifata, DeG. and Siphona gcniculata, DeG.) 
among the earliest Diptera, visiting Erigcnia bnlhosa, and the 
third (Tachiua robusta, Towns.) is a good-sized fly, which ap- 
pears regularly, though in small numbers, on the flowers of Salix 
discolor. 
The remaining species of Diptera are scattered among differ- 
ent families, none of ^vhicil produce anthophilous species in the 
strict sense of the word. These species do not depend on floral 
diet, although some of them, as for example those belonging to 
Locality. 
Southern Illinois 
Southern Illinois 
Germany 
Flanders 
Milwaukee. Wis. 
Visitors 
87 
51 
113 
43 
84 
Andrenidae 
Sysphidae. 
49 
27 
61 
15 
31 
Per 
Cent. 
56 
53 
54 
35 
37 
