202 BULLETIN OF THE BUREAU OF FISHERIES. 
GENERAL CHARACTER OF THE Diet.—On the whole there is a remarkable similarity 
in the diet of the various species. Eleven of the food items appear in all five of the 
columns and nine more are found in four out of the five. There are only three foods 
confined to a single species and three others that are restricted to two columns. 
Perhaps the most noticeable items are those which begin and end the list. Two 
species of snails are very common in all the ponds, and upon these every kind of nymph 
examined had been feeding freely. Not only had more than half of the nymphs partaken 
of these snails, but in several instances no other food was found in their digestive tract. 
With reference to the algce, it is of course understood that inasmuch as the nymphs 
catch their prey among the alge, they would be expected to swallow some of the latter. 
Hence its presence was not noted unless in sufficient quantity to make it reasonably 
certain that it had been taken voluntarily. Like the snails, in a few instances it con- 
stituted the sole article of diet. 
The other popular foods were the mayfly larve and the small crustacea, the latter 
being consumed in large quantities. 
Cannibalistic tendencies are shown by the presence of odonate nymphs in all five 
columns; and in four out of the five, nymphs were found which had eaten others of their 
own species. 
There is a good showing of beetle larve and adults, and of adult water boatmen, 
all of which are injurious to young fishes. 
SPECIFIC DIFFERENCES IN THE Diet.—Notwithstanding the wonderful agreement 
just mentioned, a careful examination reveals also striking differences in diet. Every 
one of the Anax nymphs was fully grown, with well-developed wing cases, and was 
captured in pond 4, which contained only adult buffalofish. Of course the nymphs 
could not eat these fish, and hence the absence of fish in their diet is a matter of necessity 
rather than choice. (See p. 206.) Neither did the fish eat the nymphs, however, and 
this probably accounts for the exceptional abundance of the latter, as evidenced by the 
exuvize obtained. The bulk of the food of these nymphs was made up of mayfly larve 
and snails, but it is worthy of note that they also ate large quantities of Dytiscus 
larve, the water boatman Corixa, and small crayfish. The proportion of odonate 
nymphs in their food was much greater than for any of the other species examined. 
One very large specimen had eaten nothing but crayfish, and its stomach was packed 
full of their shells and claws, which had turned red in color like a boiled lobster. The 
Dytiscus larve were identified by their heads and mandibles, Corixa by the peculiar 
color pattern of the elytra, and the Haliplid beetles also by the color pattern of the 
elytra. All three of these foods were especially abundant in this pond. 
The bulk of the food of the Libellula nymphs consisted of snails and various 
entomostraca, Cypris being a particularly toothsome tidbit; there were also quite a 
number of damselfly nymphs and a good representation of the beetle larve. <A beetle 
larva belonging to the genus Peltodyes was found to be common on the alge in the 
ponds, and its body was covered with long, jointed, bristlelike processes. The broken 
fragments of these processes were found in the gizzards of seven nymphs, in three of 
which the larvee were the only food eaten. 
In the gizzards of five of the nymphs were rounded masses of the spicules of a 
fresh-water sponge. Sponges are common in two of the ponds, and on them live a species 
of Sigara, which is a minute water boatman, and one of the caddisworms, Leptocerus. 
