1907 ENTOMOLOGICAL SOCIETY. 45 



Life-History of Dragon-flies. 



All Dragon-flies (Fig. 4.) are aquatic in their early stages and all in- 

 habit fresh or occasionally brackish water. The eggs are deposited by the 

 female upon various aquatic plants or freely upon the surface of the water, 

 either singly or in clusters of varying size, sometimes enveloped in a gela- 

 tinous mass like those of snails or frogs. On hatching the young nymphs 

 at once begin the active predaceous life which is characteristic of the whole 

 tribe. They feed upon all kinds of small aquatic life, such as other aquatic 

 insects, snails, tadpoles, or even small fish, which they grasp by means of 

 a pair of hooks at the end of the enormouslv developed labium. This struc- 

 ture when at rest is folded under the head, concealing the mouth-parts 

 like a mask, but when a small insect or other suitable animal chances to 

 pass near by, H is suddenly thrust out with lightning speed and the victim 

 drawn back within reach of the powerful mandibles (Fig. 6.). The 

 length of the nymph's life varies greatly in different species, sometimes 3 

 or 4 years being required to reach maturity. When ready for transforma- 

 tion the nymph crawls out upon some suitable support such as a rock, reed 

 or log, the choice of this support and its distance from the water's edge 

 varying in different species (Fig. 6). In a few minutes the thorax begins to 

 bulge, the skin splits along the median line and across the head, and the 

 insect gradually emerges, the thorax appearing first, then the head, wings, 

 legs and finally the abdomen ; the latter is at first comparatively short and 

 stout but rapidly elongates and at the same time the wings expand. The 

 coloration is at first very pale and indefinite and it generally requires at 

 least a day before it is fully mature. 



Transformation usually takes place early in the morning and hence 

 this is an excellent time for collecting material, for one can often get the 

 imagoes of good species, together with the exuviae of their nymphs, which 

 retain the form of the latter perfectly and are therefore invaluable as speci- 

 mens. The imagoes with their exuviae are best collected in paper bags, in 

 which they can be kept until the colors have matured. 



Nymphs (Fig. 5.) of different species inhabit different aquatic envir- 

 onments and all such should be thoroughly searched. The best apparatus 

 for general collecting is the sieve-net devised by Prof. Needham (Bull. 

 39, U.S.N.M.). This is a deep galvanized iron tray with a bottom of gal- 

 vanized wire-screen. It can be made like a rake as a combination of net 

 and sieve. 



Most nymphs are easily reared in ordinary aquaria though some require 

 running water. "We used large, glass jars, covering the top when necessary 

 with cheese cloth. A quantity of the rubbish in which the nymphs natrr- 

 ally live should be placed in the water and a few branches or boards for 

 them to crawl out upon at the time of transformation. A sufficient quan- 

 tity of aquatic plants must be used to keep the water fresh and the rubbish 

 containing the nymph's food changed once a week. 



As already observed the natural conditions which obtain in the vicinity 

 of Go Home Bay are very well adapted to the study of aquatic insect life. 

 Lying at the mouth of the Go Home River, one of the outlets of the Mus- 

 koka Lake system, it is within easy reach of a variety of different kinds of 

 aquatic environment, representing all the transitions from the open lake 

 to the sheltered river system. There are the rocky islands and reefs in the 

 open lake, wind-swept and wave-tossed and either wholly barren of vege- 

 tation or affording but a scanty sustenance to a few stunted pines, junipers 

 and other hardy plants in the crevices of the rocks, while further inland 

 there are the deep quiet waters of the bny with numerous wooded islands. 



