56 
INSECTS. 
shown at b in the figure on p. 55. This stage lasts from eight to twelve clays; 
hut 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, hut 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 Ceroplatus 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 larvas, 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 pupae. 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 Boletophila 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 gall-midges ( Cecidomyidce ) are minute, fragile insects, in 
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 (Cecidomyia 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 larvie crawl down the leaf, reach the stalk, and burrow in it to take 
Gall-Midges. 
