220 A NATURALIST IN HIMALAYA 



which I held close to it. Indeed, they seem to be 

 almost destitute of any special sense. I have seen 

 them pass and repass within half an inch of their prey 

 quite oblivious of its presence, and then, after running 

 accidentally against it, commence their fierce attack. 

 Glow-worms are active throughout the whole night, 

 not continuously, but at intervals. An hour before 

 dawn I have seen them shining in the damp fields, 

 and some, which I kept in a box, were brilliantly phos- 

 phorescent when the first rays of light were appearing 

 in the sky. 



The glow-worm is provident of its light. By day it 

 is usually extinguished ; at night its intensity seems to 

 depend on different causes. It is not the dark that 

 stimulates luminosity, for I watched glow-worms kept 

 in a dark box throughout the day and they showed 

 not the trace of a glow. There seems to be a relation 

 between general bodily activity and luminosity. An 

 energetic glow-worm is usually the most brilliant. 

 By day the insects are motionless, but I once saw one 

 of a group distinctly active in the daylight and it 

 showed a clear glow. Mechanical stimulation induces 

 luminosity. If a glow-worm is stroked on the dorsal 

 surface it often displays its light. I severed one trans- 

 versely a short distance behind the head and the 

 phosphorescence continued for two minutes after de- 

 capitation, but the muscular contractions of the limbs 

 and abdomen still remained and were quite active one 

 and a quarter hours later. The light of the glow-worm 

 does not burst suddenly into full flare as in the case 

 of the firefly. It appears gradually and comes slowly 

 to a maximum. Its disappearance is even more 

 gradual, fading imperceptibly away. Fireflies are 



