Odonata 



269 



Fig. 62. — "Boat" for rearing 

 nymphs of Ischnura verticalis. 

 (About natural size.) 



144 threads to the inch, which is fine enough to retain the smallest nymph 

 and its food organisms, and yet permits circulation of water. The silk 

 was fastened to the frame with paraffin, 

 and the frame was covered with a film of 

 paraffin to reduce "water-logging." The 

 little "sail" was a paper tag, attached by 

 a special pin, and was used to record dates 

 of molting and other data. 



The advantage of such containers, over 

 Syracuse watch glasses for instance, is that 

 the nymph has all the benefits of a large 

 vessel of water, which does not stagnate 

 so quickly, and is less subject to tem- 

 perature fluctuations. 



When the nymphs were nearly full grown 

 (i.e., in the last two or three instars) and 

 were inclined to crawl out of the boats, 

 they were transferred to glass tumblers, 

 provided with a strip of wire screen to 

 serve as a perch. Previous to transformation, the glasses were covered 

 with cheesecloth fastened down with an elastic band, thus making con- 

 venient emergence chambers in which to observe molting. 



The young imagos were then transferred to individual aquarium-cages, 

 similar to, but smaller than, the stock cages (Fig. 61 ) , one pair to a cage, 

 so that data might be kept on mating, oviposition, color changes, etc. 



Feeding. Both nymphs and adults are strictly carnivorous, and for any 

 large scale rearing it is necessary to maintain colonies of food organisms. 

 The adults have a preference for dipterous insect prey. One method 

 of supply was to stock the breeding tank with quantities of full grown 

 blood worms and mosquito larvae and pupae, and to allow the damsel- 

 flies to feed on the emerging midges and mosquitos. Later in the season 

 when this supply failed it was necessary to collect midges in the woods 

 with a net, morning and evening, and liberate them in the cages. 



For the very young nymphs, Paramecium cultures were tried and 

 abandoned. Very minute chironomid larvae were fed to the next group 

 of damselfly nymphs that hatched, with good results, and their use was 

 continued for all nymphs up to the 5th or 6th instar. The method was 

 to collect chironomid egg masses each morning from out-door troughs or 

 ponds, and to keep them in small pans of water until they hatched ; then 

 to transfer the infant blood worms with a pipette to the boats with the 

 nymphs. The nymphs seemed to thrive on them. But the blood worms 

 have a nasty habit of making little dwelling tubes out of anything they 

 can fasten down, and occasionally they would weave in the cast skin of 



