DRAGONFLIES AND DAMSELFLIES IN PONDFISH CULTURE. 201 
Such a conclusion is, of course, not warranted, and even with reference to Hschna 
itself it does not follow that it must be considered dangerous simply because it eats a 
few small fish. Needham (1903, p. 213), one of our most experienced observers, said 
with reference to 4schna constricta, which was common at Bone Pond, one of the three 
propagating ponds controlled by the Adirondack hatchery in New York, and artificially 
stocked with brook trout: “I have not been able to determine as yet whether in rela- 
tion to trout culture Aischna is more disadvantageous than otherwise. It eats a few 
fry and it eats the food of the larger trout, but, on the other hand, it furnishes a moderate 
supply of food itself for the larger trout.” In order to solve such a problem satisfactorily 
we must consider in detail all phases of the economic relations between odonates and 
fishes. An endeavor to do this has been made in the following pages by a careful con- 
sideration of the food and enemies of dragonfly and damselfly nymphs and imagos, 
by asummary of all that is known of nymphs and imagos as fish food, and by extensive 
observation and experimenting. 
FOOD OF ODONATE NYMPHS. 
The alimentary canals of 50 nymphs of each of the four dragonflies enumerated in 
the following table and 50 others of various damselfly species, making 250 in all, were 
examined to ascertain what food had been eaten. The presence in a nymph’s digestive 
tract of any of the various kinds of food listed was represented by a single unit, whether 
found in large or small quantities. The figures in the table, therefore, tell us how 
many of the nymphs had eaten any specified food, but do not indicate how much they 
had consumed. 
Foop oF 250 ODONATE NyMPHS FROM Farrport, Iowa. 
[The figures indicate the number of nymphs in which each kind of food was found.] 
a a . | a 
4/3 2/3 
f=} ° 
| h.e| a ./-3)ala 
g| ale) 4 i¢/ S| 8/4 
6| &| 8 $|a;}g] & 
: #/8)2/ 8 : S| e/a) 8 
Contents of alimentary canal. 3 3 t g a Contents of alimentary canal. 3 | 3 ‘3B a a 
s)a/E\2/s 5/4] 2/2|3 
Fle la] se) 8 Pisla]o13 
o/yr] a W)ole Tsai g 
E 4/218 g g/2/ 213) 42 
alalala Be | gai/ala 
i 
Mollusca: Crustacea—Continued. | 
Physa shells, mostly fragments... .. 16 | 6|16] 4 8 Simocephalus, sp s| 2 4 8 
Planorbis shells, mostly fragments..] r5 | 34 | 22] 4 | 12 Daphnia, sp........ a [adn 4| 17 
Beetles: Pleuroxus, sp 03. | Seal gis 5 
Miytiscns Narver eyes 2s tle. winks Zo,] 8}. a}, a}... Copepods, fragments unidentified...| 2) 2] 4| 14] 15 
Haliplid beetle, elytra of adults..... Bg [eS ler Lek Diaptomts,/spe 2. AE ht ere aS ae a | 7 6 
Peltodyes larve, jointed hairs...... crear, 10,6, | fo Seles ood Hanletiabaisst cs sovavecckedus «tee Boe Wee ty ree Mees Pe 
Diptera: CrayGSh; Spi eae. eran ot Py dhl aed eek a ale Bs 
Ceratopogon ay Be ey: See 2| 3| 6|....| 2 || Odonata: 
Chironomid larve. at he bie 8 Damselfly nymphs, unidentified....| rr TS eyes 2 
Mosquito larve.. Or he a] PAs 6 |! Ischnura verticalis nymphs......... 12,103.02] Loge 
Sammmndriarye. 32 ee! Peete ae eB Naa 9 Enallagma, sp., nymphs ........... 3) 2] 5] zl]. 
Hemiptera; Corixa, sp.,elytraofadult..|14| 4] 3] 1/|....- Lestes, sp., mymmphs,.............+5 Oth wail Saul sabes: 
Sialidse: Sialid larve................... era ag iPor isa Libellula juctuosa, nymphs........ Bh Piodd lacie gas WH. 
Perlide; Stonefly larve.............05. eee ie nee) ae ee Anax junius, nymphs.............. Bloc al Wendel ee ie: 
Ephemeride: Mayfly larve............ 27 7| 4 6 Erythemis simplicicollis, nymphs..| 6| 4] 1 |....|.... 
Crustacea: Alge: 
Entomostraca, fragments unidenti | pesmids 0! +. MAC cathe het ee 2 9/ 4] 2] 33 
Shor Poe te Se eee 5 | 21 | 26] 15] 20 Diatomsis.. 8. aioe cee te aeeeetgee (ane! amet BIE aalle= 
Cladoceran eggs, withephippium...| 2/ 7| 9] 6) 10 Sponge spicules, in masses. 7H oct: liee! ay eed Geet ces 
Bosmina, sp, 3} 8} 6] 4]. 12 CEdogonium, scattered filaments....|....]..2.]'"6 3) 14 
Cypris, sp... 6/35] 2|'20) 15 Alge filaments: 2.0.0.0. 0... 0200s 7| 7|32| x1 25 
