444 Wisconsin Academy of Sciences^ Arts, and Letters, 
As for Asilidae, these have a penchant for damseltiies which 
invariably try to escape over the water. The latter are able to 
fly exceedingly close to the surface film without touching it and 
this ability is an effective means of protection. The pursuing 
robber-fiy frequently ventures too close and becomes trapped 
by the water. It is surprising that in the ensuing struggle to 
escape from the water the robber-fly should come to lie help¬ 
lessly on its back, the wings held firmly by the surface film. 
Here, too, slight wave action may overturn the captive Asilid 
and give an opportunity to escape from the water. Hundreds 
of robber-flies were observed during the summer of 1914 trap¬ 
ped in the fashion described. 
The Hole of the Scavenger in the Lake Economy. 
In a previous portion of this paper I mentioned the fact that 
from a bulk standpoint, and much more so from a numerical 
standpoint, the scavengers predominate among the lake fauna. 
The supply of fresh plant food is comparatively restricted in 
the lake, not only in quantity but also in time, while great 
amounts of waste are accessible in the way of decaying plant 
and animal matter and inorganic waste. 
Thienemann (1911), Lauterborn (1905, 1912), and especially 
Rhode (1912) have pointed out that certain halophilous species 
of Chironomids are regularly associated with the sulfuretted 
inorganic waste of certain manufactories, while others are in¬ 
variably associated with the sewage and drainage systems of 
many cities. 
Among the halophilous species Rhode found several which are 
able to exist in inorganic waste of an especially high concentra¬ 
tion of Na and K; in fact, of a concentration exceeding that of 
sea water. (This recalls some species of Ephydridae—Aldrich 
1912). There they v/ere associated with fungi, flagellates, and 
bacteria. 
Other species were found in tremendous numbers in the 
sewage water of cities, where they were associated with Tubifex, 
and some rare fungi. In both cases, that is, in the presence of 
inorganic and organic waste, the concentration of certain mineral 
compounds was quite abnormal, and it is difficult to understand 
the possibility of life under some of the conditions found. For 
instance, an extreme was Chironomus gregarius which was 
