Art. V.—On New Zealand Glow-worms.
[Read before the Wellington Philosophical Society, 4th August, 1886.]
The following article by Mr. Meyrick appeared in the “Entomologists' Monthly Magazine,” for April, 1886:—
“A Luminous Insect Larva in N.Z.—Whilst collecting recently after dark beside a densely shaded creek near Auckland, New Zealand, I observed the precipitous earthy banks of the creek illuminated with great numbers of a larva, which has, I believe, never been reared. It resembles in general appearance an Annelid, being about an inch and a half in length, very slender, slimy, and without apparent organs; but under a microscope (as Prof. Hutton has shown me) the head appears that of a predaceous coleopterous larva—e.g., one of the Staphylinidœ. The light consists of a small light-greenish white erect flame, rising from the back of the neck. The larva burrows in the earth, exposing the head and anterior portions from the burrow, but having in front of them a sort of irregular slimy network. They occur in great numbers; I have counted fifty in a square foot of surface. The same or a similar species has been noticed in caves and mines elsewhere in New Zealand. It is impossible for a wandering entomologist to attack a larva of these habits. I should therefore be interested if any reader can give me a clue to its systematic identification. I suppose that it is carnivorous, feeding on minute insects, and I conjecture that it uses its lamp (as I do mine) to attract them, or perhaps to see to eat them.—E. Meyrick, Wellington, N.Z.—24th January, 1886.”
“[There is distinct necessity for further information (with examples in fluid) respecting the animal noticed above. The larvæ of Staphylinidœ are ordinarily so like the perfect insect in form (allowing for absence of elytra, etc.) that we venture to doubt the connection of the animal with that family.—Editors, ‘Ent. Mon. Magazine.’]”
It is extremely unfortunate that such an erroneous statement as the above, concerning one of our most interesting insects, should be the first to reach the ears of the London entomologists; and as it is the opinions of those gentlemen that will most influence us out here, I have instituted a number of observations on the insect, a summary of which I have sent in answer to the Editors' note, and propose to relate them to-night
in a somewhat more extended form. But in order that my remarks may be better understood, I will commence by stating that the Staphylinidœ are one of the most well-marked families of the Coleoptera, being none other than the famous Cocktail or Rove Beetles; their larvæ are furnished with six strong thoracic legs, a large head, and powerful mandibles, thus differing, as will be seen, in the widest possible manner from the insect under review.
Everyone who has walked in the bush at night, or, indeed, along any road at the bottom of a steep gully, cannot fail to have noticed the little points of light, mentioned as occurring in such vast numbers by Mr. Meyrick. I have not yet, however, seen 50 to the square foot of surface, although perhaps others may have been more fortunate; but, in my case, I should regard 20 of these little stars visible from one standpoint as indicating an exceptionally wealthy region.
When carefully examined with a bull's-eye lantern and pocket lens, this light is found to proceed from a large glutinous knob, situated at the posterior extremity of the larva, a fact I have verified by repeated investigations: but the insect's curious habit of occasionally travelling backwards has doubtless led to this mistake. It inhabits irregular cavities in the bank, where it hangs suspended in a glutinous web, which also appears to envelope the body, large quantities of sticky mucus being periodically shot out of the mouth of the larva, and formed into threads as required; but I have never seen anything like a net extended in front of the insect, neither have I found flies or gnats detained in the webs, although I have examined a large number. At the back of this irregular chamber the larva constructs a small hole, into which it retreats with great rapidity when alarmed.
With regard to its food, I am unable to speak, with absolute certainty on this point at present, but have little doubt that it consists of decaying vegetable matter. One individual I kept alive for eight weeks was enclosed in a small jar of mud, taken from his native bank, and placed in a caterpillar cage, where no flies or other small insects could possibly be obtained; as, however, there were some small earthworms in the mud, it might have subsisted on these, although I examined the insect nearly every night and morning and never saw it eat anything.
The light is not shown by any means regularly. On several occasions I have observed no light all the evening, and then a brilliant display at 3 or 4 o'clock in the morning, but have not noticed any peculiar meteorological conditions to affect this. As to its use, I do not think that Mr. Meyrick's explanation can be entertained, as I am sure everyone who has attracted insects at night will know how utterly inadequate such a minute point of light would be to draw them from the shortest distance. If
the larva requires a lamp to see to eat by, nearly all the New Zealand insects should have lights, as they are chiefly nocturnal. When, however, we reflect that the construction of the bee's comb is always carried on in utter darkness, the light would seem unnecessary for this purpose. If I might be allowed to suggest a use, I think it may often assist the larvæ in escaping from enemies, as when disturbed they nearly always gleam very brilliantly for a few seconds, suddenly shutting off the light and retreating into the earth. Of the pupa state I am as yet quite ignorant, as the only larva. I succeeded in rearing was left undisturbed during that condition, in order to insure the appearance of the imago. This turns out to be a small gnat, apparently one of the Tipulidœ, and not differing materially from many of those little long-legged Dipterons so often noticed on window-panes and in similar situations. The specimen, which is the only one I have as yet found, is now on its way Home for identificacation by a systematic, dipterist, and will in all probability be found undescribed.
Note.—Since the above was written, I have been informed by Baron Osten-Sacken, to whom I sent the perfect insect for identification, that it is Trimicra pillipes, the larva of which is well-known and different from the glow-worm. He still agrees, however, that the glow-worm is the larval condition of a gnat (Mycetophilidœ), and certainly not of a Coleopterous insect.—G. V. H.
Description of Plate VIA.
Fig. a. N.Z. Glow-worm; larva of a small gnat (Tipulidœ).
Fig. b. Larva of a Rove Beetle (Staphylinidœ).