210 BULLETIN OF THE BUREAU OF FISHERIES. 
amongst the rubbish, while Erythemis, Celithemis, Tramea, etc., and all the damselfly 
nymphs hide in the matted vegetation. Such lurking places also serve as admirable 
ambushes whence to secure their prey. 
3. Divinc BEETLES, WATER SCORPIONS, AND AguaTic HEMIPTERA.—These 
retaliate by eating the nymphs before they are large enough to defend themselves. 
An adult Dytiscus beetle was seen in pond 7 eating a small Erythemis nymph, which 
would partly compensate for the beetle larvee of the same species that are found in the 
table on page 201. Dr. Muttkowski has observed both Dytiscus and Zaitha feeding 
upon nymphs and noted that after capturing the nymph they invariably stick their beak 
first into its head. Garman (1917, p. 441) has recorded that ‘‘among aquatic Hemip- 
tera the genera Ranatra, Belostoma, and Notonecta, and probably others feed upon 
damselfly nymphs.’’ The fact that the water boatman, Notonecta, attacks the 
nymphs of dragonflies was also, recorded by W. J. Lucas (1908, p. 16). 
4. FRESH-WATER Hypra.—Another enemy of the nymph is found in the common 
hydra; the green species, H. viridis, does not probably reach a size sufficiently large 
to overcome even a newly hatched nymph, but the brown species, H. fusca, can and 
does eat small nymphs. Two leaves of Potamogeton ilinoiensis, which contained 
a large number of Enallagma eggs that were just hatching, were brought into the 
laboratory August 11, 1917, and placed in a small aquarium. On going over them 
with a hand lens to remove the nymphs already hatched, a large brown hydra was 
found eating one of the tiny nymphs. It was attached to the under surface of the 
leaf, nearly in the center of a large cluster of the Enallagma eggs, and could reach 
many of the nymphs with its tentacles as they emerged. If this species of hydra 
became at all plentiful in a fishpond it might kill a large number of the young nymphs. 
5. NEMATODES.—Good-sized specimens were found in the stomachs of several 
nymphs of both Anax and L. luctuosa, and Needham (1898, p. 86) found the intestine 
of a nymph parasitized by large Gregarines a millimeter in length. An Enallagma 
nymph examined July 27, 1917, contained a dozen large Gregarines, and several others 
contained one or two apiece. These intestinal parasites probably never become numer- 
ous enough to actually kill their host, but their presence may weaken the nymph and 
make it more susceptible to its other enemies. 
6. Parasitic MITES AND FLIES.—Some of the Ischnura and Enallagma nymphs 
were found infested with small mites between the wing pads and around the bases 
of the legs; 10 of these were taken from a single Ischnura nymph. 
Mrs. Aaron (Lamborn, 1890, p. 50) mentioned another small red mite “which 
skims rapidly over the water in search of an Odonat egg, upon which it either deposits 
an egg or excavates it for immediate nourishment.” She also saw one of the parasitic 
Diptera ovipositing on the egg of Diplax. In these two cases, of course, the larve of 
the mite and the fly when they hatch feed upon the dragonfly’s egg. 
Needham (1903) reported that many hymenopterous parasites prey upon the eggs 
of Lestes, which are inserted in plant tissues above the water line, where they are exposed 
to such attacks. He succeeded in rearing three species of the parasite, belonging to 
different genera. 
Brandt (1869) similarly reported rearing another parasite, Polynema ovulorum, 
from the eggs of Agrion (Calopteryx), and added that half the eggs were sometimes 
destroyed in this way. 
einai 
