THE DIPTERA. 49 



Family 



The Glow-worm. Bolitophila luminosa t Skuse. 

 (Frontispiece, fig. i). 



Every one who has walked in the forest at night has no 

 doubt noticed, in many damp and precipitous situations, 

 numerous brilliant points of greenish white light shining 

 out from amongst the dense undergrowth. The animal 

 which causes this light may be seen at Fig. la on the 

 Frontispiece, and is probably one of the most interesting 

 insects we have in New Zealand. It inhabits irregular 

 cavities, mostly situated in the banks of streams, where it 

 hangs suspended in a glutinous web which is stretched 

 across the cavity and supported by several smaller threads 

 running right and left, and attached to the sides and ends 

 of the niche. On this the larva invariably rests, but when 

 disturbed immediately glides back along the main thread 

 and retreats into a hole which it has provided at the end of 

 it. From the lower side of this central thread numerous 

 smaller threads hang down, and are always covered with 

 little globules of water, constituting a conspicuous, though 

 apparently unimportant, portion of the insect's web. It 

 should be mentioned that all these threads are constructed 

 by the larva from a sticky mucus exuded from the mouth. 



The organ which emits the light can easily be seen by 

 referring to Fig. la. It is situated at the posterior ex- 

 tremity of the larva, and is a gelatinous and semi-trans- 

 parent structure capable of a great diversity of form. It 

 can be extended or withdrawn at the will of the larva, 

 which, however, can shut off the light independently of 

 this latter action. Larvae cease to shine on very cold 

 nights, in the daytime, and in a room which is artificially 

 lighted. They gleam most brilliantly on dark, damp 

 nights, with a light north-west wind. These larvae appear 

 to suffer great mortality in a state of nature, as the 



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