Art. XVI.—On the Varieties of a common Moth (Declana floccosa).
[Read before the Wellington Philosophical Society, 13th June, 1888.]
Seeing that the variation of Lepidoptera is attracting so much attention in England at the present time, more especially in its relation to the origin of species, it occurred to me that perhaps a few remarks on one of our moths (Declana floccosa) might be of some interest, especially as it seems not unlikely that we are here actually witnessing the gradual evolution of several distinct species from a single one of a very unstable character. I must, however, begin my remarks by stating that my information on the subject is at present very limited, the varieties of this insect which actually exist being doubtlessly very much more numerous than those which I have here figured and described. My chief object in writing this paper is not so much to give information, as to arouse a more active interest in a subject which I feel is far too comprehensive to be dealt with by myself alone.
With respect to the normal type of Declana floccosa, it is extremely hard to say much, as the several varieties do not contain any characters common to all of them, although, in many instances, the same markings can be recognised in several different forms. Thus we have nothing definite which can be said to form the basis of the species; our only course, therefore, is to take the simplest form, and regard that as the type. Pl. ix., figs. 7 and 8, represent this form. The following is a brief description: Front wings pale greyish white covered with numerous brownish-black streaks, exhibiting a slight concentration towards the tip of the wing, but varying much in intensity (compare figs. 7 and 8). Hindwings buff-coloured, shaded with pale brown towards their exterior margins. Next in order to this most simple form is the variety depicted at fig. 1, which exhibits several large round spots on the disc of the front wing, the minute streaks being decidedly concentrated on the hindmargin, and leaving the central portion of the wing considerably paler in colour than in the usual type. From this form we will now pass to an insect which was long known as Declana nigrosparsa, from the numerous black spots ornamenting its frontwings. It is a tolerably common and easily recognised variety (fig. 4).
Pl. ix., fig. 2, represents another very characteristic form of D. floccosa, distinguished from the type by the two conspicuous stripes which cross the forewings from the costa to the inner margin; one being situated near the thorax, and the other at about two-thirds of the distance towards the hindmargin, this latter being doubly curved. A further development of this form is drawn at fig. 5, where these two stripes are joined together, near the middle, by two lines running parallel with the hindmargin and costa of the wing. These two varieties were described under the name of Declana junctilinea, Mr. Meyrick having subsequently shown in his paper on the New Zealand Geometrina,* that they were inadmissible as species. A form combining the characters of nigrosparsa and junctilinea is shown at fig. 3, where we have both the curved lines and numerous black spots. Finally, we have a most conspicuous form (fig. 6), showing the greatest deviation from the original type, where the frontwings are entirely suffused with dark greyish-black, except two broad bands of the original light colour extending from the costa to the inner margin. The base and hindmargin of the posterior wings are also much suffused with dark-grey, leaving a broad ill-defined band of lighter colour across the middle of the wing.
Taking now a general view of these varieties it is manifestly impossible to regard them as constituting more than a
[Footnote] *“Trans. N.Z. Inst.,” vol. xvi., p. 49.
single species, the numerous intermediate forms between the most marked of them rendering any attempts at subdivision completely futile. At the same time, I am led to believe that the larvæ of two of the most distinct types of variation—namely, nigrosparsa and junctilinea, exhibit considerable differences, although I have not yet reared a sufficient number to form any decided opinion on the subject. The larvæ of figs. 1, 4, 7, and 8, including the type and two varieties, feed on the New Zealand “currant” or “wineberry” (Aristotelia racemosa), and are of a dark reddish-brown colour, sometimes marbled with grey, closely resembling the twigs of the trees, and thus affording the caterpillars the usual protection from enemies. On the other hand, the larvæ of the vars. figs. 2 and 5 are light yellowish-brown with irregular darker markings, approximating closely to the stems of the manuka (Leptospermum), on which I have always found them. To any one interested in the development of species and inheritance of parental peculiarities, I think that this insect would be a most useful object for investigation. The fact that none of the varieties I have mentioned are confined to any particular sex would be most advantageous, as the experimentor could readily select a male and female of each conspicuous form from which he could obtain ova, and thus ascertain whether the well-marked peculiarities of the parents were inherited, or, in other words, whether there was any tendency to establish a permanent or specific character. Should it be found feasible to carry the observations through several generations of moths, I feel sure that the result obtained would have an important bearing on that much-vexed question, the origin of species.
Before concluding, I should like to point out how eminently suitable insects are for investigations of this character. In the first place their brief life enables the industrious observer to watch the same family of insects for several generations, an impossibility in the case of most other animals, while the conspicuous characters which distinguish the majority of the species, especially of the Lepidoptera, render any departure from the normal type at once perceptible. It is consequently somewhat surprising that they have been so little made use of, and it can only be attributed to that prejudice which unfortunately exists against the study of entomology even in the present day. Workers in most of the other branches of science are allowed to push their investigations far beyond the limits of direct usefulness, and are encouraged for their zeal and perseverance in so doing, whereas, in the case of the entomologist, unless the insects he is investigating are connected with agriculture or some other matter of equal importance, his labours are regarded as a mere waste of time. With respect to this idea, I can only say that, if the same utilitarian argu-
ment, which is applied so unsparingly to the entomologist, was used in every instance, I think that we should soon find that the majority of our most cherished studies and recreations might be readily dispensed with, and our lives consequently reduced to a condition of miserable monotony.
In England, I am happy to say, entomology is being more appreciated every day, the number of entomologists having increased enormously during the last twenty years. The Entomological Society of London alone consists of over three hundred members, while there are at least three other larger societies in London devoted almost exclusively to the same science. Surely a few inquiring minds in New Zealand will turn their attention to a study which offers a boundless field for investigation, coupled with inexpensiveness and plenty of out-of-door recreation.
Description of Plate IX.
Figs. 1–8. Varieties of Declana floccosa.