As the insects rest on the grass and moss, the difference in the amount of light emitted is quite marked. While the luminous spot indicated by a female is quite bright, the males show only as the palest fire. When on the wing, the light of the latter is not seen at all. Heavy rain, so long as it is warm, serves only to increase the brightness. The seat of the light of the glow-worm is in the tail, and proceeds from three luminous sacs in the last segment of the abdomen. The male has only two of these, and the light proceeding from them is comparatively small. During favourable weather the light glows steadily, but at other times it is not constant. The fireflies of the tropics--those comprising the genus _Lampyridæ_--vary to the extent that while certain species control their light, others are without this power. The light of our English glow-worm is undoubtedly under its control, as upon handling the insect it is immediately put out. It would seem to take some little muscular effort to produce the luminosity, as one was observed to move continually the last segment of the body so long as it continued to shine. The larvæ of the glow-worm is capable of emitting light, but not to be compared to that of the developed insect. Both in its nature and immature forms, _Lampyris noctiluca_ plays a useful part in the economy of Nature. To the agriculturist and fruit-grower it is a special friend. Its diet consists almost wholly of small shelled snails, and it comes upon the scene just as these farm and garden pests are most troublesome. British fireflies probably have never yet figured as personal ornaments to female beauty. This is, and has always been, one of their uses to the dusky daughters of the tropics. They are often studded in the coiled and braided hair, and perform somewhat the same office as diamonds for more civilised belles. Spanish ladies and those of the West Indies enclose fireflies in bags of lace or gauze, and wear them amid their hair or disposed about their persons. The luminosity of our modest English insect is far outshone by several of its congeners. Some of these are used in various ways for illumination, and it is said that the brilliancy of the light is such that the smallest print can be read by that proceeding from the thoracic spots alone, when a single insect is moved along the lines. In the Spanish settlements, the fireflies are frequently used in a curious way when travelling at night. The natives tie an insect to each great toe; and on fishing and hunting expeditions make torches of them by fastening several together. The same people have a summer festival at which the garments of the young people are covered with fireflies, and being mounted on fine horses similarly ornamented, the latter gallop through the dusk, the whole producing the effect of a large moving light.