14 



KNOWLEDGE. 



January, 1913. 



favoured localities during the summer months, this 

 is not always the case. 



I have proved by actual experiment that the larvae 

 have the power of emitting light from the moment 

 that they leave the egg. 



As the young larva increases in size, so the light- 

 giving area of the anal segments becomes larger and 

 also brighter, so that it is at times almost 

 impossible to tell whether the light in the grass 

 proceeds from a larva or a perfect female. 



If the light of a full-grown female larva be closely 

 compared with that of a perfect female, the 

 former will be found to be smaller and also of a 

 more greenish colour. 



With regard to the duration of the light there is 

 also a decided difference ; for the light of the perfect 

 female may continue to shine steadily for several 

 hours when undisturbed, i.e., from dusk until 1 a.m. 

 or even an hour or so later; whereas in the larval 

 form it is seldom that one finds the light shining 

 continuously for more than a few minutes. 



Glow worms, like ants, are very sensitive to vibra- 

 tion, and when approaching them in the grass one 

 must not tread heavily, or they will extinguish their 

 light and thus be lost to view. 



This applies to the larvae as well as the perfect 

 females. 



If you pick up a female glow worm and turn it 

 about in your hand, it feigns death and its light 

 remains extinguished until all apparent signs of 

 danger are past. Whilst it is still in the larval form, 

 this insect behaves in quite a different manner under 

 similar circumstances ; for when turned about in the 

 hand, it generally lights up at once, the light 

 gradually dying away, but reappearing again and 

 again as often as the insect is disturbed. It will 

 light up in the same manner if the glass or box, or 

 other vessel in which it has been placed, is smartly 

 tapped with the fingers. 



The glow worm larva will also give forth its light 

 if it is sprinkled with cold water, or suddenly 

 immersed in the same, while it is also apparently 

 influenced by the effects of lightning, as I venture 

 to think the following particulars will prove. 



For several years I have been working at the life- 

 history of the glow worm, and with this object in 

 view I had, at the end of July, 1911, about a 

 hundred and fifty larvae of L. noctiluca, all of them 

 having been hatched between June 23rd and July 

 27th of that year. 



These larvae were fairly evenly distributed in four 

 glass tumblers. Each glass had a closely-fitting lid 

 made of cardboard and fine wire gauze, and also 

 contained a small moistened root of grass. 



The four glasses containing these larvae were kept 

 on the shelf of a hanging book-case in our sitting- 

 room, in a rather dark corner about seven feet above 

 the floor, and near a window facing east. 



These tiny larvae would give forth a very small 

 spark of light, if they were disturbed by tapping on 

 the glasses, or even by tapping the shelf on which 

 the glasses were kept. 



On the evening of July 29th, 1911, we had a 

 storm with thunder and much lightning, and as I 

 happened to be at home, I thought I would see if 

 the lightning had any effect on the larvae; having 

 previously read a brief account* stating that glow 

 worms were affected by it. 



For an hour, from 8.15 p.m., when the lightning 

 flashes were very frequent, I kept the larvae under 

 observation. The unusual amount of electricity in 

 the air certainly appeared to effect these larvae, for 

 tiny bright greenish lights kept appearing and dis- 

 appearing from first one glass and then another, 

 right throughout the time that I was watching them. 

 Occasionally there would be lights showing in all 

 four glasses at one and the same time, when from 

 six to twelve distinct points of light could be seen ; 

 at other times there would be only three or four 

 lights visible. 



No doubt many more of the larvae were affected 

 in a similar manner; but their light would be hidden 

 by the intervening roots and blades of the grass, 

 amongst which they were generally to be found. 



None of the flashes of light lasted more than a 

 second or two, and they were all produced without 

 any mechanical disturbance of the larvae. 



The window was partly open, and although the 

 hour was not very late, the corner of the room where 

 the larvae were kept was dark enough for their 

 lights to be clearly seen. The lightning had not 

 ceased at 9.15 p.m. ; but as we lighted the lamp at 

 that time, the display of miniature fire-works could 

 no longer be seen. 



I watched and waited on many evenings after- 

 wards, to see if the display would be repeated under 

 normal weather conditions, but without result. 



On the 19th of the following month (August, 

 1911), however, there was another storm in the 

 evening with lightning, and the glow worm larvae 

 acted in exactly the same manner as they did on the 

 29th July. 



Unfortunately, I was prevented from making any 

 further experiments in this direction, owing to my 

 glow worm larvae all gradually dying off during last 

 autumn and winter. 



At the present time I ha^ve several hundred fresh 

 larvae, hatched during July and August, 1912 ; but 

 the warm thundery weather suitable for carrying out 

 further experiments in this direction is still lacking; 

 and here I will leave the matter for the present. 



See Nature, October 1st, 1903. 



