104 HEAT AND LUMINOSITY OF INSECTS. 



heat ; but some of these animals, in certain circumstances, give 

 out a quantity sufficiently considerable to raise their temperature 

 perceptibly. This is the case with Bees, when they are 

 disturbed in their hives ; and it is noticed that their Respira- 

 tion then becomes very active. (See ANIMAL PHYSIOLOGY, 

 410, 411.) 



621. Another most remarkable phenomenon, of which the 

 cause is not fully known, is the production of light ; which is 

 observed amongst some Insects. Of this the Lampyris, or 

 Glow-worm, is an example, which is well known to almost 

 every one who frequents our fields. The male has wings and 

 is not luminous ; but the female, which is destitute of them, and 

 which is often found on banks and hedges during the summer 

 evenings, sheds a phosphorescent light that is often very brilliant. 



In another species of Lampyris 

 which inhabits Italy, the indi- 

 viduals of both sexes are at the 

 same time winged and luminous ; 

 but this singular property is 

 especially remarkable among cer- 

 tain Fire-flies, which live in the 

 warm regions of America, and 



FIG. 328 MALE AND FEMALE GLOW- , . , , , n ,1 



WORM which produce, when flying in the 



darkness, a natural illumination of 



the most brilliant effect ; they are often placed by women in 

 their hair as ornaments ; and we are told that the Indians use 

 them to light themselves, when they travel by night. Among 

 our Glow-worms, the light proceeds from certain spots situated 

 upon the upper part of the two or three last rings of the abdo- 

 men ; whilst among the Fire-flies, it comes from analogous spots 

 placed upon the prothorax or corslet. It appears that the insect 

 can vary at pleasure the intensity of this phosphoric light ; and 

 that it continues during a certain time, when the animal is placed 

 in a gas unfit for respiration, or even in a vacuum ; but that it is 

 extinguished in cold water. 



622. The sexes are distinct amongst these animals, and there 

 often exist very great differences between the male and female ; 



