414 Wisconsin Academy of Sciences, Arts, and Letters. 
Family Dytiscidae. 
In the earlier part of summer, late May to the middle of July, 
adults of Bidessus flavicollis Leconte, Coptotomus interrogatus 
Fabricius, Hydroporus undulatus Say, and Laccophilus macu- 
losus Say, are not at all uncommon in the lake. Individuals 
of Agabus and Colymbetes may occur, but rarely. Since ad¬ 
joining ponds, creeks, swamps, and basins are on the whole 
copiously provided with larvae of Laccophilus, Acilius, Cyb- 
ister, Agabus, etc., although entirely absent from the lake, it 
is probable that such adults as are found in the lake have mi¬ 
grated into it and have not bred there. In specially favored 
spots where shelter permits some emergent plants to gain a 
foothold one may find some Dytiscid larvae. 
The difference between the lake and other aquatic communi¬ 
ties is very marked in late summer, when sheltered water such 
as the lagoons in the parks and the several ponds and creeks 
about the lakes teem with young Dytiscid larvae of several 
species, while such larvae are conspicuously absent from the 
lake. As a food factor the Dytiscidae are therefore negligible 
so far as the lake is concerned; but this does not apply to creeks 
and rivers. i 
Family Hydrophilidae. 
Only a single species, Berosus sp. (probably striatus Say), is 
represented in the lake, and this species is quite rare. The 
larva occurs in sandy depths up to six meters. I was able to 
breed the species and discovered that the pupa is aquatic and 
a water-breather like the larva; but the emerged adult es¬ 
caped before I had seen it. In the fast current just below the 
Yahara spillway, the species seems to thrive; at least, fish taken 
at the spot frequently contained larvae of Berosus. 
Family Gyrinidae. 
The larvae of the Gyrinidae, like Berosus, seem to find con¬ 
ditions optimal in the current below the Yahara spillway. In 
that stream, too, the adults are exceedingly abundant, occur¬ 
ring in enormous swarms composed of many thousands of in¬ 
dividuals. Although an adult Gyrinid is occasional in the lake, 
no larvae have as yet been found. 
