Holder, in his work on phosphorescent animals, either quotes or refers to Prescott as saying that “when the Spaniards visited the country”—that is, Mexico, “the air was filled with the cucujo, a species of large beetle which emits an intense phosphoric light from its body strong enough to enable one to read by. These wandering flies, seen in the darkness of the night, were converted by the excited imagination of the besieged into an army of matchlocks.” Surely, from such a foundation, something as superior to it as are our cultivated fruits, or domestic breeds, to the wild stocks from which they sprung, might in no long time be produced, since it is not to be supposed but that some individuals of the Pyrophorus give a stronger light than others. The above passage, by the way, if it be from the Conquest of Mexico, as one might suppose it to be, is most carefully concealed in the index, which, however, it might very well be, and yet exist, as I know from much teasing experience. As to the matchlocks, would to Heaven the old Mexicans, as well as the Peruvians, had had them, or, still better, 11-inch Howitzers. I might then have something more to say about these wonderful beetles. All I can add now is that the light appears to be used by the insect as a guide to its own movements, since when the celebrated Dr. Dubois covered one of the side ones with wax, this caused the individual so treated to walk in a curve, and when “both spots were covered it soon stopped, and then moved in an uncertain manner, carefully feeling the ground with its antennæ.”[[151]] But I do not know if “both” here means all three of the lamps, or only the two upper ones.
If there be any luminous insect that eclipses the Pyrophorus it must be the great lantern-fly—also of South America—provided only that the great lantern-fly is luminous. That is a most essential point, and it does not appear yet to have been satisfactorily made out. The principal evidence on the affirmative side is that of Madame Merian, who was right about the Mygale—the great bird-killing spider—and who here speaks as an actual eye-witness. Her account is as follows: “The Indians,” she says, “once brought me, before I knew that they shone at night, a large number of these lantern-flies, which I shut up in a large wooden box. In the night they made such a noise that I awoke in a fright, and ordered a light to be brought, not knowing from whence the noise proceeded. As soon as we found that it came from the box we opened it, but were still more alarmed, and let it fall to the ground in a fright at seeing a flame of fire come out of it; and as many animals as came out, so many flames of fire appeared. When we found this to be the case we recovered from our fright, and again collected the insects, highly admiring their splendid appearance.”[[151]]
Here, then, is a definite statement, from which all possibility of mistake seems excluded, if, as I suppose is the case, there is no doubt as to the specific identity of the insect which was the subject of it, and which is thus described by Mr. Holder in the work already mentioned: “The Fulgora lanternaria of South America,” he tells us, “is nearly three and a half inches long from tip of head to extremity of tail (i.e. abdomen), and almost five and a half inches broad with its wings expanded.” Truly a goodly insect, of right portly dimensions, and if it be not really luminous—upon occasions, at any rate, for it certainly is not so generally—it is so much the greater pity. But to continue: “The body is of a lengthened oval shape, while the head is distinguished by a singular prolongation, which sometimes equals the rest of the body in size.” This is a most remarkable appendage, if it may be called so, hollow and with a blown-up, inflated sort of look. It does, indeed, to some extent resemble a Chinese lantern, and seems made to be lighted up. The colour, too, suggests this, since it is striped longitudinally with red and yellow, presenting quite a gala appearance. Accordingly, it is said to be here that the luminous property of this strange insect exists. This is its lantern, and, by reason of it, it has received its name of lantern-fly.
And yet, since that night when Madame Merian had her interesting experience, we meet with no one, apparently, who can unequivocally say that he has seen the Great Lantern-Fly with its lantern alight. On the other hand, we have some second-hand statements which have almost the value of first, such as that of M. Westmael, who “assures us that a friend of his observed the luminosity”;[[151]] whilst “John C. Branner, PH.D., states that when in South America he was often informed that it was luminous, but never could find anyone who had personally seen the light.”[[151]] The curious thing is that there are other lantern-flies belonging to other parts of the world, and in regard to them too we have the same doubt and discrepancy, the same assurances and general belief, the same categorical denials. Thus a distinguished authority on the subject of phosphorescence— Dr. Phipson—in referring to the smaller Chinese species, Fulgora candelaria—the candle-fly—says: “It is from these appendages, the sides of which are transparent, that the phosphoric light appears.” And again: “It is said also that the trunk of a tree covered with numerous individuals of Fulgora candelaria, some in movement, others in repose, presents a very grand spectacle, impossible to describe, but which may be witnessed sometimes in China.”[[151]] It would seem, too, that there exists a Chinese edict which forbids young women to keep these candle-flies; and if this is not with the idea of preventing their use as signals, or of checking vanity, it is difficult to see what the object of such an enactment can be.
Lastly, we are told by Packard, in his Guide to Insects, that “Mr. Caleb Cooke, of Salem, who resided several years in Zanzibar, Africa, told me that the lantern-fly is said by the native to be luminous. They state that the long snout lights up in the night, and in describing it say its head is like a lamp (keetchwa kand-tah).”
All this evidence appears to me to point in one way, and one way only—I mean, of course, in its entirety, since otherwise it points in two ways. But even if it is possible that in one country alone an insect—well known and conspicuous—can have got the reputation of being luminous without really being so, at least occasionally, this can hardly have come about in regard to the same, or some allied insect, in three or four countries. Added to this we have Madame Merian’s direct evidence, but, on the other hand, it is perfectly clear that these insects are not always, or even generally, luminous. The conclusion, then, seems irresistible that they occasionally are so, that, for some reason or other, the phosphorescent principle is active in them only at certain times or seasons. Why this should be so we do not know, but there is nothing inconceivable in it; and some other animals—for instance, centipedes—would seem to be luminous at some times and not at others.
The so-called lantern or snout being a very remarkable organ, for which some use must be assumed, the likelihood of its sometimes becoming a lamp would be increased considerably, if, so far as we knew, it performed no other office. This was how the case stood till lately; but in 1899 there was the Skeat Expedition for scientific purposes to the Malay Archipelago, and on its return Mr. Nelson Annandale propounded a theory in regard to the more ordinary use, at least, of the organ in question, which was based on his own observation. His account is as follows: “The curious anterior prolongation of the head in many genera of the Fulgoridæ has long puzzled entomologists. At Biserat, in Jalor, I was fortunate enough to observe the real use of this peculiar structural modification. On the morning of May 30th I noticed a specimen of Hotinus spinola seated on the trunk of a Durian tree in the village, and incautiously attempted to catch it in my hand. The insect remained almost still, merely drawing in its legs towards its body and pressing the claws firmly against the bark, until I had almost touched it. Then it lowered its head with very great rapidity, flew up into the air without spreading its wings, and alighted on the roof of a house six feet behind a tree, and considerably higher than its position on the trunk had been. At the time I did not notice anything peculiar in the way in which this Fulgorid jumped, for there are many large species of the same family which, without being provided with long noses, can leap for a considerable distance by means of their legs only; but as I was examining my specimen (a dead one) I was struck by an indentation or crease that ran across the central region of the nose at right angles to its main axis. Then I discovered that at this point, and at this point only, it was flexible, and that if the tip of the nose and the dorsal surface of the abdomen were pressed together between the finger and thumb, and then suddenly released, the insect would not fall straight to the ground, but would be propelled for some distance through the air before doing so, just as would be the case if a piece of whalebone were treated in like manner.”[[152]]
Mr. Annandale then goes on to show, or to suggest, that the Fulgorid—as he calls it—by pressing its snout—or lantern—against the tree-trunk, and at the same time pushing itself off from it with its legs, “would fly into the air at a tangent,” and he continues: “I have no doubt that this is substantially what occurs in the case of Hotinus; but in the living insect the action is far too rapid for the eye to discriminate its details, and dead specimens cannot be made to leap in this way because it is impossible to force the legs to perform their part of the action.”[[152]] Such, then, is the theory, but as other members of the family jump in much the same way, to all appearance, without any such apparatus, and since the bending of the head, at such a moment, might be correlated with the movements requisite to produce such a leap as this, it certainly wants confirmation.
Some of the finest displays of luminosity have been observed in centipedes, which although not insects, may be counted such for the purpose of this volume. Thus M. Audouin, noticing one night a light proceeding from one of his chicory-fields, “ordered his man to turn up the earth, when the scene that followed is described as truly magnificent. The soil appeared as if it had been sprinkled with molten gold, the display being intensified if the insects were trodden upon or rubbed. In the latter case streaks of light appeared, as if a bit of phosphorus had been placed upon the hands, the light being distinctly visible for twenty seconds.”[[153]]
Mr. Brodhurst, again, referring to another species—Geophilus electricus—about an inch and a half in length, and in the daytime inconspicuous enough, says: “The light looked like moonlight, so bright was it through the trees. It was a dark night, warm and sultry. Taking a letter, I could read it. It resembled an electric light, and proceeded from two centipedes and their trails. The light illuminated the entire body of the animal, and seemed to increase its diameter three times. It flashed along both sides of the creature in sections, there being about six, from head to tail, between which the light played, moving, as it were, perpetually in two streams. The trail extended one and a half feet from each centipede over the grass and gravel walk, and it had the appearance of illuminated mucus. On securing one of the creatures for examination, I found on touching it the light was instantly extinguished.”[[153]] The display is, therefore, voluntary, nor could Mr. Brodhurst ever get his centipedes to shine in captivity.