478 A DESCRIPTION OP 
These flies are as luminous as a lighted torch, and re- 
flect a lustre on all neighbouring objects. They are in 
continual motion during the night ; but this motion is 
various and uncertain, alternately rising and sinking. 
They commonly hover about six feet from the ground. 
It is said that not a night in the year occurs in which 
they are not seen ; but in winter they are more frequently 
observed than in summer. Neither rain nor snow pre- 
vents their appearance. From all these circumstances, 
many have erroneously supposed them to be merely the 
ignis fatuus, or jack-o'-the-lantern, which exhales from 
marshy lands, over which it is seen to hover in the night. 
THE COCHINEAL INSECT. (Coccus cacti) 
THE Cochineal insect is of the same genus as the scale 
insect on the vine, which looks like a little bit of wool 
attached to the branch, but which, when pressed, stains 
the fingers with a red liquid. The Cochineal insect in 
the like manner affixes itself to the leafy stems of the 
nopal-tree, a kind of opuntia, or prickly-pear, common 
in Mexico and South America, whence the Cochineal 
used in Europe is principally imported. 
When the Mexicans have gathered the Cochineal in- 
sects, they put them into holes in the ground, where they 
kill them with boiling water, and afterwards dry them in 
the sun ; or they kill them by putting them into an oven, 
or laying them upon hot plates. From the various 
methods of killing them arise the different colours in 
which they appear when brought to us. While they are 
