LIFE HISTOEY OF HYDROUS ( HYDROPHILUS) TRIANGULARIS. 



33 



where specimens of the same bass are often kept under experimentation. In every 

 instance the larva was instantly seized and swallowed, sometimes almost before 

 it struck the surface of the water. This indicates that not only do these fish eat 

 the larvae, when they can get them, but that the larvsB ought to make successful 

 bait when fishing. 



ENEMIES OF THE PUP.^:. 



It might seem at first sight that the pupa was admirably protected by being 

 buried in the moist earth, but even there it is subject to certain dangers. The first 

 of these is from ants. Two pupse were unearthed in July that were half eaten up 

 by small ants, which literally filled their pupal chambers. Of course, a larva 

 when ready to pupate will seldom choose an ants' nest in which to form its pupal 

 chamber, and it will not often happen that ants drive one of their galleries into a 

 pupal chamber after it is formed; but the finding of these two half -eaten pupae 

 shows that this does happen occasionally, and the larger the number of ants along 

 the shores of a pond the greater are the chances of its occurrence. 



Another and much more serious danger for the pupa lies in a change in the 

 moisture content of the earth in which the pupal chamber is built. If the amount 

 of moisture in the soil is greatly changed in either direction, it is likely to prove fatal 

 to the pupa. If it be raised excessively, then the chamber will be flooded and the 

 pupa will be drowned. It is to guard against this very accident that the pupa skin 

 is provided with the long curved spines described on page 24, while the pupa also 

 arches its body strongly upward in order to lift the spiracles above any ordinary flood- 

 ing. However, the pupal chamber is never far from the water's edge, and any con- 

 tinued rise in the water will flood it so completely that these safeguards will no longer 

 avail. Two pupal chambers on the shore of pond 2, series E, were filled with water, 

 and as a result the two pupae they contained were drowned within a few minutes. 



On the other hand, the soil that was moist enough when the larva began its 

 pupal chamber may become baked and dried by the time the adult beetle is ready 

 to emerge, and the latter may thus become imprisoned and unable to get out. The 

 abrupt draining of this same pond 2, series E, caught some beetles in just this way. 

 As long as the water remained at its normal level the soil would have continued soft 

 and moist; but when the water was entirely removed the hot sun soon dried and 

 baked the mud so firmly that the adult beetles were caught and imprisoned in the 

 pupal chamber. Two were found thus imprisoned on August 12. They were alive 

 and vigorous and would possibly have remained so until released by the resoftening 

 of the earth after the pond was filled again. Similarly, a piece of moist earth from 

 the pond shore containing three pupae of Berosus, another hydrophilid genus, was 

 brought into the laboratory July 16. It was not known at the time that it con- 

 tained these pupae, and after it had served its purpose it was allowed to become dry 

 and hard. When thrown out on August 15, it broke and revealed three live adult 

 beetles^ which could never have escaped through their own efforts. 



In The Canadian Entomologist for January, 1894, Ashmead published the 

 descriptions of two new hymenopterous parasites from water beetles. These had 

 been reared by H. F. Wickham — one from the pupa of a Gyrinus species and the 

 other from the pupa of Dineutes assimilis. Similarly, half a dozen hymenopterous 



