56 



IXSECTS. 



shown at b in the figure on p. 55. This stage lasts from eight to twelve days ; 

 but the perfect insect is shortlived, the female surviving apparently only long- 

 enough to pair with the male and lay her eggs. 



When speaking of one of the true midges reference was made to a pathological 

 case of phosphorescence, but in the present family there are two instances known 

 of the normal occurrence of this phenomenon — not, however, in the adult insect, but 

 in the larval or pupal stages. The first instance is furnished by < -eroplatus sesioides, 

 a midge, which although not yet known to occur in England, has been met with in 

 several of the countries of Europe. Here the luminosity is said to resemble that of 

 the glow-worm, but proceeds from the entire animal, and from members of both 

 sexes. The larvae, which are found in small colonies on the under side of a fungus, 

 exhibit, when crawling in the dark, a moving streak of light, less bright than that 

 emitted by the pupa?. The insect also shines when lying in the cocoon, so long as 

 its abdominal rings are still transparent and have not attained their complete 

 colouring. The cocoons themselves are not luminous, but allow the light to be 

 transmitted as through a paper lantern ; and since as a rule several of them are 

 situated together a more extensive glow is displayed, whereby both the cocoons 

 themselves and the surrounding objects are illuminated. When the insect is about 

 to emerge from the cocoon, the luminosity gradually diminishes, and ultimately 

 ceases altogether. The second instance is presented by a New Zealand midge 

 called Boletojphila luminosa, the larva of which is known as the "glow-worm." 

 Here the female is luminous in all three stages of its existence, but in the male 

 the luminosity disappears two or three days before the emergence of the perfect 

 insect. The luminous organ, which is situated in the posterior part of the body of 

 the larva, consists of a gelatinous, semi-transparent structure, capable of extension, 

 contraction, and other changes of form, and, like its luminosity, is completely under 

 the animal's control. As to the part played by this organ in the midge's economy, 

 authors are at variance ; one believing that the light serves to attract small 

 creatures, so that they become entangled in a web of mucus, which the larva 

 suspends in some niche in the soil. 



The gull-midges (Cecidomyidce) are minute, fragile insects, in 

 Gall-Midges. . . 



which the wings are furnished with few veins, are often hairy, and 



always fringed on the edges. From an agricultural point of view, these insects are 



the most important of all the gnat-like flies, since much damage is at times done to 



crops by their larvae. The most notorious is the Hessian fly (( '(■'■it/omi/ la destructor), 



represented in its various stages in the accompanying illustration. This insect was 



believed to have been introduced into North America by the Hessian troops at the 



time of the War of Independence, whence the inhabitants of the United States 



gave it the name by which it is now commonly known. The adult female, which 



measures rather less than a tenth of an inch, is mostly of a velvety black colour, 



varied with blood-red, especially on the abdomen ; while the rather larger male is 



browner, with the red clearer. These flies may be observed on the wing during 



the second half of April. They live, however, only for a few days, and perish soon 



after laying their eggs, which amount to about eighty or a hundred. These are 



placed separately or in pairs upon the leaves of the wheat-plant, and in a short time 



hatch, when the larva? crawl down the leaf, reach the stalk, and burrow in it to take 



