The Zoologist/4th series, vol 1 (1897)/Issue 673/Earthworm Studies III. Phosphorescence and Luminosity

by Hilderic Friend

 

EARTHWORM STUDIES.

By the Rev. Hilderic Friend,

Author of 'Flowers and Flower-Lore.'

 

III. Phosphorescence and Luminosity.

 

Among the various members of the Animal Kingdom which possess the power of emitting a phosphorescent glow are certain inhabitants of Wormland, to some of which we wish to draw attention. The notice of the public, so far as my researches show, was first directed to the subject in the year 1670 by Grimm; but scientific observation was then scarcely known. Later came Flauguergues in 1780; his paper on the phosphorescent light of Earthworms appearing in 'Lichtenberg's Magazin' in the German language. It may also be seen under the French title "Sur la Phosphorésine des Vers de terre" in 'Rozier Journ. de Phys.,' xvi. (1780) pp. 311–313. In 1873 Cohn's observations on the same subject were published in the 'Zeitschrift fur Wissenschaft. Zoologie,' vol. xxiii. pp. 459–461, and entitled "Leuchtende Regenwürmer"; while numerous recent writers have further contributed to our knowledge, especially in relation to the continental species. Thus in 1872 an article appeared in the French 'Ann. Sci. Nat.' ser. 5, t. xvi. by Panceri, entitled "Etudes sur la phosphorescence des animaux marins," in which he states that the luminosity observed in the case of certain worms is due to a secretion from the girdle where special glands exist, and that with the evolution of light there was no perceptible raising of the temperature. In this respect, therefore, the glow corresponds with that emitted by the Firefly, Noctiluca, and Glowworm. One investigator at least has tested the colour and composition of the luminosity by the spectroscope, and says that it is not unicolored or monochromatic, but compounded chiefly of the red and violet rays. Other students regard the substance which produces the light as homogeneous.

In 1838 Eversmann published an article in Russian on a night-shining worm (Lumbricus noctilucus, see Zapisk. Kazan. Universit., 1838, pp. 156–7), and in 1871 Breese, an English naturalist, delivered an address on the Earthworm before the West Kent Natural History Society, from a meagre abstract of which we learn that he had spent some years on the subject of annelid luminosity, having studied it historically from the year 1805, when Viviani wrote on the phosphorescence of the sea, down to the date of his own investigations. According to Breese the luminosity exists in the excreted glutinous material with which the outer skin of the animal is covered. It is much to be regretted that (so far as I can learn) the researches of this naturalist have never been given to the public in detail.

More than one creature has at different times borne the name of the phosphorescent worm. In 1837 Dugès, a French writer, described a species under this name (Lumbricus phosphoreus) with a girdle extending from the 13th to the 16th segments, and a somewhat flattened body behind. After the lapse of exactly half a century this curious creature was examined again, and named by Giard Photodrilus, or the luminous worm. It has eight setææ just as our common species have, but they are separate, and not in couples. There is no gizzard, nor does the lip dovetail into the segment behind. It is a small, transparent, rose-coloured worm, and decidedly phosphorescent.

A paper on this worm by Barrois appeared some time ago under the title "Sur la presence du Lumbricus (Photodrilus) phosphoreus, Dugès, à Groffliers (Pas-de-Calais)" in the 'Revue Biolog.,' iii. pp. 117–119. Beddard places it under the genus Pontodrilus, and gives the following brief summary of its characters and history:—

"Definition.—Length 50 mm.; diameter 2 mm.; number of segments 110. Setæ in eight rows. Clitellum xiii.–xvii. Hearts in x.–xii. Sperm-sacs in xi., xii. Spermathecæ in ix. with a diverticulum. Habitat—France.

"This species has been investigated by Giard, who, however, has not yet published an illustrated account of his researches. The main facts in its structure are given in the above definition. In addition to the points there mentioned there exist on segments xii., xiii., and xviii. sacs of modified setæ in addition to the ordinary ventral setæ; instead of a bundle of about four setæ there is sometimes only a single seta. This worm appears to be luminous at night, whence the name given to it by Dugès."—Beddard, 'Monograph of Oligochaeta (1895),' p. 472. It is now known as Pontodrilus phosphoreus (Dugès).

In 1843, when the British Association met at Cork, specimens of an annelid were exhibited by Dr. Allman, which he had discovered in the bogs of the south of Ireland, and which was the cause of a luminous appearance. When irritated the worm gave out a phosphorescent light, which is said to have been much increased by exposing the creature to the vapour of alcohol. The light was of that peculiar soft greenish hue which is characteristic of the phosphorescence usually observed in living animals, and familiar to most readers in connection with the Glowworm. It was said to be closely allied to the Earthworm. Another gentleman was reported to have observed the same pecularity in some annelids which exist in the bogs of Connaught. I have been unable to find any recent reference to or confirmation of these curious observations, and this though I have examined many hundreds of specimens of terrestrial and aquatic worms from different parts of Ireland, have made special enquiries, and even visited Ireland myself in 1896 purposely to examine the annelid fauna for the Royal Irish Academy. Ten years later Mr. Henry Cox exhibited an Earthworm which was phosphorescent at a meeting of the Literary and Philosophical Society of Liverpool, held November 14th, 1853.^[1]

While few records of a reliable nature respecting the observation of luminous worms in Britain are available, a good deal has been done by our continental fellow-workers. Vejdovsky, who wrote a very valuable work on the various species of annelids in 1884, entitled 'System und Morphologie der Oligochæten,' gives us some results of his personal experience, which I believe have never been placed before the English reader. He says that he had the good fortune once to observe an interesting case of phosphorescence in connection with the Brandling. It was one warm July night in 1881, when he was exploring a dung-heap. (Naturalists do not usually work with kid gloves and diamond rings.) Presently a spot of soft, bluish white light appeared, which, however, was changeful and unsteady. Now it would disappear, then return anew and shine forth over a larger space, though never with a brilliant hue. He thereupon removed a portion of the manure from the spot where he had observed the luminosity, and found that the light appeared brighter, and shone for a longer time without disappearing, or before it migrated to another spot. By means of a lantern Vejdovsky was able to secure a large number of specimens of the Brandling from the dung-heap, which he placed in a vessel for the purpose of subjecting them to careful observation. To his great surprise he found that his finger soon glowed in the darkness with the phosphorescence, which extended generally over the hand where it came into contact with the worms. It was therefore apparent that the luminosity was the product of a fluid secreted by the cutaneous glands, which had attached itself to the hand of the investigator, and now manifested itself in this curious way.

We have an interesting observation on the same subject by Prof. Von Stein, which was published at Leipzig in 1883. One evening in the middle of September, the Professor was spending some time with a circle of friends at a parsonage not far from Potsdam, when the conversation turned upon phosphorescence and the phenomena of light. Hereupon one of the younger members of the family—who are usually the keenest and most shrewd observers of Nature, and the best friends of the naturalist —remarked that there were fountains in the adjoining gardens, the water from which was frequently observed to be full of lightbearing creatures when it was violently agitated. He regarded the affair at first simply as a hoax, or an attempt to make a fool of him,—as people are ever ready to do with a hobby rider,—but ascertained eventually that the luminosity was due to the presence of a species of Worm which possessed the property of shining when disturbed. As with Vejdovsky, so with Prof. Von Stein, the finger which had come into contact with the Worm continued to glow for some time after. What species of Worm was under observation is not recorded.

In the 'Report of the British Association' for 1887 (p. 767) we have a note by Mr. Harker "On a Luminous Oligochæte." But here again the same remark applies. Much good work, alas! is rendered valueless for want of a little accuracy in nomenclature.

It now becomes a question what end could be served by the possession of this property. The philosopher no sooner learns a new fact than he begins to pry into the secret which lies beneath, and stands to it as cause to effect. We have analogy to guide us. The water worms may be compared with the marine animals which produce phosphorescence, while the Brandling may be studied in the light of a Glowworm. It may be objected that as worms, except in a few rare cases, have no eyes there can be no advantage in their luminosity. But such an argument would be based on the erroneous assumption that a creature without eyes is incapable of receiving impressions from light. That worms are influenced by light is proved both by their habit of avoiding it, and by the experiments which have been carried out by various students. Darwin remarks that as worms are destitute of eyes he at first thought that they were quite insensible to light. He found, however, that "light affects worms by its intensity and by its duration." Hoffmeister states that, with the exception of a few individuals, worms are extremely sensitive to light, and from my own observations I have been able to demonstrate that there are marked differences in the susceptibility of the different species—some being very much more susceptible than others.

Now it follows that if a number of species of worms lived together in one place, as they usually do in a manure-heap, it would be a great advantage for a given species to possess a distinguishing feature, such as that of luminosity, to enable two individuals to discover each other's whereabouts, just as the male Glowworm detects the female by the light emitted from her upturned abdomen.

Viewed in this light, a new field of research is opened up which hitherto has been totally unworked, but which may be hoped to yield remarkable results if diligently, patiently, and intelligently tilled.

It will not be out of place in this connection to quote from the 'Gardeners' Chronicle' of January 9th, 1847, some very interesting remarks by Mr. J. Wighton on insect luminosity, seeing that many cases of phosphorescence attributed to worms really come under this head. He says:—

"The Centipede (Scolopendra electrica, L.) is one of the few luminous insects met with in this country. Its specific name electrica seems to be a misnomer; lucifera or phosphorifera would be more applicable. It would take a large number of Centipedes to give a sensible shock, even supposing the creature capable of doing so at all. In other electric animals, as the Torpedo, no flash appears, even when they give a discharge strong enough to stun a horse; still less do they shine with the steady light of the Centipede or the Glowworm. The luminosity of the Scolopendra electrica appears to proceed from a clammy slime exuded from the body of the insect, which is analogous to the phosphoric mucus that comes from the skin of certain fishes in an early state of decomposition. Like that, it may be removed from the surface from which it proceeded, and objects smeared with it become luminous. Walking one damp night on a dark road, I picked up something shining from the ground; I screwed it up in paper, and took it home. On unfolding the paper a Centipede crawled out and escaped, leaving its phosphoric slime adhering to the paper. It is doubtful for what purpose this secretion is given to the insect. It can hardly be to attract the opposite sex, as its habits are mostly subterranean, appearing to feed on dry halfdecayed roots and leaves, and in no way injurious to living vegetation, but probably beneficial by admitting air into the soil, and preparing dead organic matter to be more quickly suited for the food of plants. Some mention that it is carnivorous, feeds on small insects, and like the Lithobius forcipatus, or 'Fifty-foot,' of which it is said that it wounds its prey with a venomous fluid emitted from its claws, but I think this cannot be relied on. Indeed it is difficult to do more than guess at the final causes of many curious phenomena among animated beings. One author (De Geer) says that it is by no means certain that the light of the Glowworm is given it for the purpose of inviting the male, because he has proved that the female insect can shine in its infant state, in that of larva, and even after it has taken the form of nymph. But the same sort of reasoning would lead us to conclude that, because milk is found in the breast of a new-born babe (a singular fact, best known to every nurse), when it cannot be required to give suck, therefore the same child is not to give suck when she has become a woman, and has children of her own.^[2] The light of the Glowworm proceeds from a lantern in the under side of the tail, protected by a transparent skin. The researches of such an anatomist as Swammerdam would probably find a dark shutter or slide between the glass of the lantern and the lamp within, moveable at the pleasure of the insect. If you crush a Glowworm while it is shining, the light will smear about exactly like that of the Centipede. I have never tried the experiment by day, or at times when they do not shine. The Glowworm appears to know, by an unerring instinct, the proper time for it to begin its exhibition, which is shortly after sunset. I have repeatedly kept them all day long in a dark cellar without being able, by the gloom or the coldness, to make them withdraw their curtain; but on returning in the evening, I have found them glittering as brightly as in their native copse. The best way to keep them in confinement is to have a live turf at the bottom of a glass globe. All day long they remain hidden close to the earth, but at the appointed hour of evening they will mount the blades of grass as high as they will bear them, turn up the ends of their tails, and display a splendour more steady and beautiful than either gas or camphine. The duration of their performance is very variable, sometimes not more than half an hour, sometimes till what the Scotch call the 'sma' hours.' Whether this depends upon the weather or the health of the creature, is best known to itself. After a while, also variable, they lay their eggs among the turf, and themselves in the dust, to shine no more. So briefly perish these stars of the earth, in fit contrast with those of heaven, glittering as they do, through ages upon ages, with undimmed and never-tiring lustre."

It is curious that among all the suggestions which have been offered to account for the luminosity of the worm we find no mention of the use of phosphorescence for protection. When the water was agitated, Von Stein's worm became luminous. Was not that protective? The enemy of the Centipede, Glowworm, or annelid would fear the fire, and keep at a respectful distance. The Brandling, tit-bit of Trout and other fish, may readily be supposed to exhibit a luminous skin when attacked or affrighted; and the fact that these lowly creatures seldom appear luminous except when irritated or exposed to danger, apparent or real, lends probability to the idea that the phosphorescent display is protective. A light flashed out in time of danger would scare a would-be intruder, which would soon become used to a regular light and learn its innocuousness. If, as Pietro Martire tells us, the people of the West Indies were alarmed when they met a fellow in the dark whose face had been smeared with the phosphorescence of an insect, it is not unreasonable to suppose that a Trout would be alarmed if a Brandling suddenly lighted its lamp. Further observation on this subject is greatly to be desired. At present it is far from being as complete as the scientist could wish. In the 'American Naturalist' (vol. xxi. p. 773–4) is a note by Mr. G. F. Atkinson entitled "A Remarkable Case of Phosphorescence in an Earthworm," which I have unfortunately been unable to consult. Reference may also be made to Moniez's paper in the 'Rev. Biol.,' i. pp. 197–200, Kirby and Spence's 'Introduction to Entomology,' and Secchi, 'Nouv. Observ. in Ann. Sci. Nat.,' series 5, vol. xvi., 1872, p. 68.

 

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1. See 'Proceedings,' No. viii., p. 57. In 1893 I received news of a phosphorescent Worm having been found in London, but it proved on examination to be not a Worm at all. In fact, many of the instances of so-called phosphorescence in worms may be traced to the popular habit of calling centipedes and all other lowly wriggling creatures by this comprehensive name.
2. An illustration and argument drawn from Kirby and Spence.