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Art. XXXIX.—Life History of Epyaxa rosearia, Dbld.
[Read before the Wellington Philosophical Society, 23rd September, 1885.]
The object of this short paper is to describe the life history of the above moth, and also to correct some errors in Mr. Meyrick's description of the adult insect. These errors are not the result of inaccurate observation, but of having bad specimens. This moth, although not distinguished by bright colouring, is interesting, as being one of those species in which the male and female differ much in colour. So much do they differ, that in the case of most, if not of all, these species the male and female were at first described as distinct species; but this is not so remarkable, for one of these authors has given as many as ten different names to one species.
Taking now the three stages of this insect:
The egg is oval, smooth, and of a pale yellow colour.
The caterpillar is a looper—that is, it has pro-legs only on the 10th and 13th segments; and two specimens of it were found about the 1st of August, nearly full-grown, on water-cress in the mouth of an old mining tunnel near the Waterworks.
Description of caterpillar.—Length, at rest, about three-quarters of an inch. Colour light-green, with indistinct whitish longitudinal lines, and a narrow median dorsal stripe of the ground colour, edged on each side by one of these whitish lines; a subdorsal whitish line on each side of the median stripe; the ground colour shows again as a lateral line, edged below with whitish. Under-side with delicate whitish or yellowish longitudinal tracings, as on the upper side. The junctions of the segments show yellowish or whitish rings when the larva contracts.
Head, greenish-yellow. Body tapering somewhat to the head.
Chrysalis enclosed among the withered leaves of the cress above ground; very dark brownish-black, glossy.
A pair of the perfect insects emerged about the second week of September. Mr. Meyrick's descriptions are evidently taken from more or less faded cabinet specimens: hence there are errors unavoidable in the case of a naturalist not having access
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to fresh specimens. In specimens kept for some time the male is, as he describes, pale whitish-grey, with the median band of the forewings more or less distinctly outlined with black, especially opposite the cell; while the female is ochreous or of a pale sandy colour, with faint traces of the usual markings.
But in quite fresh specimens the insects are much more ornamental. The male is darker than above described, usually of a rosy or warm-tinted grey as ground colour in the forewings. The outer side of the basal patch and both sides of the median band are edged with a greenish-yellow line, showing distinctly on the unfaded ground-colour. The fringes are also rosy-grey. Mr. Meyrick states that the male is very constant in colour and the female variable; but the reverse is rather the case, faulty specimens having led to this misstatement, for the female suffers most when preserved in a cabinet. The true colour of the forewings of the female is dull yellowish-green; but the common methods of killing—for instance, by bruised laurel leaves—destroy the colouring of green moths. Collectors may note this caution against exposing fine green moths to the fumes of prussic acid. By lantern light the female seems to be of a glaucous or peculiar blueish green, which serves at once to distinguish it. The green colour of the female seems dingy and faded if placed beside the rich green of Cidaria similata, but if compared with the dull greys of allied Geometrina it seems peculiar and noticeable. The ordinary markings are not very distinct in the female. The hindwings are often a dull blackish-grey. The yellowish colour ascribed to the female is merely the common colour of faded green moths. The two sexes are more dissimilar in their fresh state than when faded; and the green colour of the female may serve as a very efficient protection whilst among foliage.