GLOW-WORM, a small insect, remarkable for its shining in the dark. See CICINDELA.
The male and female of this species differ greatly from each other. The male has wings, and is a small fly: the female has no wings, but is a large crawling worm.—The body of the male is oblong, and somewhat flattened; the wings are shorter than the body; the head is broad, dun, and flat; the eyes are large and black. This has no light issuing from it, and is not commonly supposed to be at all akin to the glow-worm. The female is what we expressly call by this name. This is a very slow-paced animal, somewhat resembling a caterpillar: the head is small, flat, hard, black, and sharp towards the mouth. It has short antennæ, and six moderately long legs. The body is flat, and is composed of twelve rings, whereas the body of the male consists only of five. It is of a dusky colour, with a streak of white down the back. It is often seen in the day-time, but is not known till dark; at which time it is easily distinguished by the glowing light, or lambent flame, that is seen near the tail, issuing from the under part of the body. It is commonly met with under hedges; and if carefully taken up may be kept alive many days upon fresh turfs of grass, all which time it will continue to shine in the dark.
The light of this little insect is so strong, that it will shew itself through several substances in which the creature may be put up; a thin pill-box easily shews it through, and even though lined with paper the light is not impeded by both. The creature is sluggish, and appears dead in the day-time; and its light is not distinguishable even if carried into a darkened room, unless the creature be turned upon its back and disturbed, so as to be put in motion, and then it is but very faint: after sun-set the light returns, and with it the life and motion of the creature. The motion and light of this insect indeed seem in some measure to depend upon one another: it never shines but when its body is in some sort of motion; and when it shines most, the body is extended to one third more than its length in the day-time. In the time of brightest shining it will sometimes of a sudden turn its body about, and the light will not be longer than the head of a pin; and, on being touched, she will then immediately extend herself, and the light will become as large and as bright as ever.
Flying Glow-Worm, (cicindela volans.) In the war-
mer months of the year, this creature is sometimes caught in our houses flying to the flame of a candle; and examined in the dark is found to be luminous at these times, tho' perhaps less or not at all so at others; which may be a reason of its not being known though caught in the fields; and to this it may be owing, that many who have described this creature, have thought it not a native of Britain. Without wings, it is frequently enough found in form of the common glow-worm, and then always shines. Aldrovandus informs us, that it lays eggs which in a short time hatch small worms; and that these afterwards become flies, by the same sort of change which happens to butterflies and other species of winged insects. Mouffet, and Thomas Bartholine, give much the same description with Aldrovandus, but allow the male only to have wings. Julius Scaliger, however, contradicts this, and affirms that he has caught them both winged in the act of generation; but this is not acknowledged even by all those who have quoted the abovementioned passage from Scaliger. Mr Waller, in the philosophical transactions, confirms Scaliger's account, having observed them in the same manner in the act of copulation both winged; only with this difference, that the female was the larger of the two, which is the case with many other insects. The male and female in this winged state both shine in hot weather, and their light is so vivid that it may easily be seen even when there is a candle in the room. The vibrations of this light are irregular, and its colour greenish. The luminous parts are two small specks under the tail at the end, and the light continues in these some time after the tail is cut off; but then gradually goes out. The parts of insects continue alive in some degree for a considerable time after they are separated from the rest of the body; and probably the light of the tail of this animal continues just as long as this sort of life remains in it.
The use of this light seems to be to direct the animal in its course, and in the taking of its prey; and to this purpose it is admirably placed. The tail is easily bent under the belly, and then throws the light full upon any object about or under the head of the animal; and the eyes are placed, not on the upper part, but on the under side of the head; so that they have all the advantages of it, while the light in this part is not offensive to the eyes, as it naturally would have been if carried before the head. Upon occasion the insect can cover this light, so that its enemies cannot take the advantage in order to pursue it.
The insect is of the beetle kind, of a brown or dusky colour. It has hard case or shell wings, as the other beetles have; and, when these are expanded, there appears a pair of very large membranaceous ones. Its head is covered with a sort of shield or broad-brimmed hat; under this hat are placed the eyes, which are black and large, and are moveable, so that the creature can upon occasion thrust them forward to the sides of the hat or covering of the head. It has two hairy antennæ; and its legs are like those of the common fly, hard, shelly, and hairy. Its eyes afford an elegant object for the microscope, being composed of an infinite number of lenses, like those of the libellæ and other insects.