WATER BEETLES IN RELATION TO PONDFISH CULTURE. 
235 
how far they are able to overcome adverse conditions. It may also be extremely 
useful in suggesting available food upon which they can be reared during experi- 
mentation, but it does not indicate their natural food preference any more than a 
prison menu indicates the preferences of a convict. The food of the species here 
given is to be understood as the result of observations made in the ponds. What 
they were known to eat in the laboratory is so stated and is included for the reasons 
just given. 
Much also can be learned under artifical conditions about the methods em- 
ployed by the different species in the construction of their pupal chambers; but 
the distance they travel from the water’s edge and the kind of a location they 
choose can be judged only by finding the pupae in situ on the shore of the pond. 
The same is true of the materials used. There is no sand on the shores of any 
of the ponds, and of more than 100 pupal chambers of Dineutes americanus col- 
lected during the last three s umm ers, every one was made of moist earth pellets. 
Yet when six larvae, whose freshly made pupal chambers had been hopelessly broken, 
were transferred to a suitable terrarium and each constructed a new chamber, two 
used entirely moist sand instead of earth pellets. The methods employed with 
both materials were exactly the same, however. 
ECOLOGY. 
MODIFICATIONS OF STRUCTURE AND VESTITURE. 
All beetles that live in the water show some modifications of structure and 
vestiture to fit them for their aquatic life. This fact was noted by Leng (1913, 
p. 32) in a paper on aquatic Coleoptera in the Journal of the .New York Entomo- 
logical Society. He added that the modifications were more noticeable in the 
adults than in the larvae. These modifications serve varied and quite different 
uses and may be concerned with locomotion, with sex activity, with flotation, 
with respiration, and with sight. They can be considered most conveniently in 
connection with the various functions they assist. 
LOCOMOTION. 
The beetle larvae can all walk, but none of them move fast enough to warrant 
the assertion that they run. Most of them can swim, and a few can jump; that is, 
they can throw the body a short distance by kicking with the legs or by suddenly 
flexing the posterior portion of the abdomen. The relative locomotor ability of 
the various larvae is given under each species separately. In general, the dytiscid 
larvae are excellent walkers and swimmers, and some of them can jump. The two 
species of Laccophilus are the best walkers and the most agile larvae of all those 
studied, the two species of Thermonectes are the best jumpers, and the Cybister 
larva is the most active swimmer. The hydrophilid larvae are fair walkers and 
good swimmers, but none of them so far as known can jump. The gyrinid larvae 
are good walkers and excellent swimmers, while the Dineutes larvae can jump, 
although not as well as the Thermonectes larvae. The haliplid larvae can only 
crawl, they can neither swim nor jump, and all their movements are extremely 
