DOUBLE LIGHT OF THE FIREFLY. 161 



abdomen is relaxed, by the overlapping of the metathorax. 

 When the insect is placed on its back, it throws itself into the air 

 like other Elaters ; but if it be made to repeat this many times, 

 it appears to become weary, and endeavours to raise itself by 

 bending the head and the abdomen back, so as to rest on the 

 extremities, in hope to roll over. It is when thus recurved that 

 the abdominal light suddenly appears, the oval space being un- 

 covered. When held in the hand, the same effect is produced by 

 forcibly bending back the abdomen with the fingers ; but this is 

 not very easy of accomplishment, on account of the resistance of 

 the closed elytra ; but if these be held open with one hand and 

 the abdomen recurved with the other, it is readily shown. 



" As the open space, then, can be exposed only when the 

 elytra are expanded, the reason is manifest why the red light is 

 never displayed by the insect when walking or resting: the 

 green thoracic light, on the other hand, may be displayed at any 

 time ; it is, however, very rarely shown during flight. On one 

 occasion two or three glow-flies, having entered the sitting- 

 room in the evening, gave out the red" light most brilliantly as 

 they flew round near the ceiling, the spectators being beneath 

 them. One of these, being alarmed by my efforts to capture it, 

 gave out the thoracic light also very brightly ; and the mingling 

 of the red and green light in the evolutions of flight produced 

 an effect indescribably beautiful. 



" That the thoracic light is subject to the will of the insect is 

 indubitable ; but whether the same can be predicated of the 

 abdominal light I am not assured. During flight it is every 

 second intermitted, as far as the observer can detect; but its 

 appearance or disappearance may depend upon whether the dorsal 

 or ventral surface is presented to the eye. This is when, soon 

 after dark, the insect is sweeping in rapid, headlong, irregular 

 curves over the fields or along the edges of the forest ; when the 

 appearance resembles that of a stick with the end on fire (but 

 not in flame), carried or whirled along by one running swiftly ; 

 quenched suddenly, after a course of a dozen yards, to appear 

 again at a similar distance. When slowly flying over the grass, 

 the progress of one may often be traced by the red glare on the 

 ground beneath ; a space of about a yard square being brilliantly 

 illuminated, when no light at all reaches the spectator's eye from 

 the body of the insect. 



M 



