BRITISH FIRE-FLIES.
ALTH017GH Britain can show no parallel, either in number or brilliance, to the living lights of the tropics, we are not without several interesting phosphorescent creatures of our own. Those whose business leads them abroad in the fields and woods through the short summer nights are often treated to quite remarkable luminous sights. Last night the present writer was lying on a towering limestone escarpment, waiting to intercept a gang of poachers. The dark- ness was dead and unrelieved, and a warm rain studded every grass-blade with moisture. When the day and sun broke, this would glow with a million brilliant prismatic colours, then suddenly vanish. But the illumination came sooner, and in a different way. The rain ceased, and hundreds of 'tiny living lights lit up the sward. In the intense darkness, these shone with an unusual brilliancy, and lit up the almost impalpable moisture. Every foot of ground was studded with its star-like gem, and these twinkled and shone as the fire-ffies stirred in the grass. The sight was quite an un-English one, and the soft green glow only paled at the coming of day. One phase of this interesting phenomenon is that now we can have a reproduction of it nightly. The fire-ffies were collected, turned down on the lawn, and their hundred luminous lamps now shed a soft lustre over all the green.
Why our British fire-flies are designated " glow-worms " is difficult to understand. Lamp yris noctiluca has nothing worm- like about it. It is a true insect. The popular misconception has probably arisen in this wise. The female glow-worm, the light-giver, is wingless; the male is winged. The latter, however, has but little of the light-emitting power possessed by the female. Only the light-givers are collected, and being destitute of the first attribute of an insect, wings, are set down in popular parlance as worms. Old mossy banks, damp hedgerows, and shaded woods are the loved haunts of the fire-flies, and the warm nights of the soft summer months most induce them to burn their soft lustre. Some widowed worm or fire-fly flirt may shed her luminous self on the darkness even MI into dying summer or autumn. But
this is unusual. It is not definitely known what purpose is served by the emission of the soft green light, but it has long been suspected that the lustre was to attract the male. And this seems reasonable. Gilbert White found that glow-worms were attracted by the light of candles, and many of them came into his parlour. Another naturalist by the same pro- cess captured as many as forty male glow-worms in an evening. Still another suggestion is that the phosphorescence serves as a protection or means of defence to the creatures possessing it, and an incident which seems to support this view has been actually witnessed. This was in the case of a carabeus which was observed running round and round a phosphorescent centipede, evidently wishing, but not daring, to attack it. A third explanation of the phenomenon is that it serves to afford light for the creature to see by. A somewhat curious confirmation of this is the fact that in the insect genus to which our British fire-flies belong, the Lampyrid.w, the degree of luminosity is exactly in inverse proportion to the development of the vision.
Fire-ffies glow with greatest brilliancy at midnight. Their luminosity is first seen soon after dark :— " The glow-worm shows the matin to be near, And 'gins to pale his ineffectual fire."
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 pro- ceeds 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 favour- able weather the light glows steadily, but at other times it is not constant. The fire-flies of the tropics—those com- prising the genus Lampyridx—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 con- tinually the last segment of the body so long as it con- tinued to shine. The larva of the glow-worm is capable of emitting light, but not to be compared to that of the developed insect. Both in its mature and imma- ture forms, Lantpyris 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 when these farm and garden pests are most troublesome. British fire-flies probably 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 the diamond for more civilised belles. Spanish ladies and those of the West Indies enclose fire-flies 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 ibe read by that proceeding from the thoracic spots alone, when a single insect is moved along the lines. In the Spanish settle- ments, the fire-flies 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 fire-flies, and being mounted on fine horses Similarly ornamented, the latter gallop through the dusk, the whole producing the effect of a large moving light.
Another phosphorescent little creature found commonly in Britain is a centipede with the expressive name Geophilus electricus. This is a tiny living light which shows its luminous qualities in a remarkable and interesting fashion. It may not uncommonly be seen on field and garden paths, and leaves a lovely train of phosphorescent fire as it goes. This silvery train glows in the track of the insect, sometimes extending to 20 in. in length. In addition to this, its phosphorescence is exhibited by a row of luminous spots on each side of its body, and these points of pale fire present quite a pretty sight when seen under favourable circumstances. It was stated that the light-giving quality of the fire-flies might be designed to serve them to see by ; but this fails to apply to the little creature under notice, as it is without eyes.
There are still other British insects which have the repute of being phosphorescent, though the evidence is not yet quite satisfactory. Among them are the male cricket and "daddy-long-legs," both of which are reported to have been seen in a phosphorescent condition. But if there is a dearth of phosphorescent land creatures which are native„this has no application to the numerous luminous creatures living in our Southern British seas. Among marine animals the phenomenon is more general and much more splendid than anything which can be seen on land, as witness the following picture by Professor Martin Duncan :—" Great domes of pale gold, with long streamers, move slowly along in endless procession ; small silvery discs swim, now enlarging and now contracting, and here and there a green or bluish gleam marks the course of a tiny but rapidly rising and sinking globe. Hour after hour the procession passes by, and the fishermen hauling in their nets, from the midst drag out liquid light, and the soft sea jellies, crashed and torn piecemeal, shine in every clinging particle. The night grows dark, the wind rises and is cold, and the tide changes; so does the luminosity of the sea. The pale spectres sink deeper, and are lost to sight, but the increasing waves are tinged here and there with green and white, and often along a line, where the fresh water is mixing with the salt in an estuary, there is brightness so intense that boats and shores are visible. But if such sights are to be seen on the surface, what must not be the phos- phorescence of the depths ! Every sea-pen is glorious in its light ; in fact, nearly every eight-armed Alcyouarian is thus resplendent, and the social Pyrosoma, bulky and a free swimmer, glows like a bar of hot metal with a white and green radiance."
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