10 
BULLETIN OF THE BUREAU OF FISHERIES. 
Station, Fairport, Iowa, when one of the small fishponds was drained. While the 
water was receding and immediately after the pond was emptied, about 100 fully 
developed larvse of Hydrous triangularis were obtained, together with numerous 
specimens in younger stages. Six egg cases were found, of which one contained 
half a dozen newly hatched larvae, another was full of undeveloped eggs, and the 
remaining four were empty. 
From the shores of the pond, just above the former water line, were obtained 
15 pupae in various stages of development. Several of the mature larvae were 
observed digging their way into the earth as the water lowered, and these were 
closely watched until they transformed into pupae. Some of the pupae were preserved 
at once, others were left until they emerged as adult beetles. In this way the entire 
life history was obtained, together with many suggestive facts in reference to the 
habits. Fifty larvae, including some smaller ones, were cut open and the contents 
of their digestive canals carefully examined to ascertain their ordinary food. 
Owing to these unusual facilities for observation it has been possible to solve prac- 
tically all the problems connected with the life history, including some that have 
hitherto remained unanswered by the European observers. 
MATING AND EGG LAYING. 
The mature beetles almost certainly live through the winter, and mating and 
egg laying begin in the early summer and continue at least until the last of July. 
No female has yet laid more than one batch of eggs in captivity, 
f but it seems probable that at least some of them do this in their 
natural environment. 
The eggs are in the form of an elongated ellipsoid, 4.25 to 
4.5 mm. long and about 1 mm. in diameter (fig. 1), and are 
bright yellow in color when first laid. As is the custom with 
many of the Hydrophilidse, the eggs are inclosed in a silken 
case. In the present species this case is attached to floating 
leaves, bits of trash, etc., and not to living plants, and it floats 
upon the surface of the water. 
The construction of one of these cases was described for the 
European species by Lyonet (1832) and afterwards by Miger and 
Lancret (1804). Something evidently was lacking in the aqua- 
rium experiments of these observers, because the formation 
of the egg case required a very long time — five hours for the 
female watched by Lyonet and three hours for the one watched 
by Miger. Possibly the European species is a slower worker 
than the American, or one female may work more slowly than 
another. At all events the following observations made by 
George B. Lay in the Fairport laboratory, July 27, 1916, and witnessed in large 
part by the present author, show that a case can be constructed much more rapidly 
than this. 
A female Hydrous triangularis was noticed starting an egg case at 1 p. m. in 
one of the laboratory aquaria. She abandoned this effort, however, as there were 
Fig. 1— Side view of a 
single egg. 
