The markings of this species appear to be developed in a precisely
similar manner to those of _D. Vespertilio_. The adult larva, as in
the last species, shows no trace of a subdorsal line. A row of large
black spots, each having an irregular round, yellowish-white nucleus,
is situated on an olive-green, blackish-brown, brown, or dirty yellow
ground. I have, unfortunately, also in this case been unable to procure
fertile eggs. There is, however, one figure of a caterpillar, 2.5
centimeters long, by Hübner, which is of a light green colour, and has
five longitudinal lines; one dorsal, two subdorsal, and a spiracular
line. The subdorsal is white, and bears in the place of the ring-spots
small red dots, whilst the line itself is bordered with black where the
red spots are situated. Hübner has probably figured the third stage,
so that we may venture to conclude that in the second stage there is
a subdorsal line either quite free from spots, or only showing such
feeble rudiments as are to be seen in the second stage of _Vespertilio_.
I found two specimens in the fourth stage in the Upper Engadine.
One of these (Fig. 45) was already of a dark, blackish-green
ground-colour[91] with a broad, greenish-white subdorsal line sharply
defined throughout its entire length, and containing ring-spots of a
sulphur-yellow with an orange-red nucleus; the black “ground-area” did
not encroach upon the subdorsal line, but was confined to two faint
crescents situated above and below the “mirror.” Only the two foremost
“mirrors” (on the second and third segments) were without nuclei.
The remaining peculiarities of coloration are shown in the figure. I
may here only point out the shagreening present on the sides and a
portion of the under surface.
The specimen figured was 3.3 centimeters long; a second example
measured 2.8 centimeters in length, and was essentially similar, but
showed that a considerable amount of variability must prevail at this
stage of development. It was pitchy black, with a very indistinct
subdorsal line and a few ring-spots, the “mirrors” of which were also
sulphur-yellow, with the orange-red nucleus. The shagreening was quite
as strong as in the first specimen, the dots being yellow instead
of white. It is specially to be observed, because of its important
theoretical bearing, that in this larva the ring-spots were absent on
the three front segments, and on the fourth only, a faint indication
of one could be perceived. In the caterpillar figured the ring-spots
increase also in distinctness from the tail to the head.
_Fifth Stage._
The two specimens just mentioned, after moulting, acquired the
well-known markings of the adult caterpillar already briefly described
above. The fifth is the last stage.
The larva is known to occur in several variations, Rösel having figured
it in three forms; light green, olive-green, and dirty yellow. It has
not been since considered worth the trouble to attend to the subject of
caterpillar coloration. Thus, Wilde,[92] in his well-known work, takes
no notice of Rösel’s observation, but simply describes the caterpillar
of _Galii_ as “blackish olive-green.”
Having had an opportunity of observing twenty-five adult specimens of
this somewhat scarce species at one time, I am able to state that it
is not in this instance di- or polymorphism, but a case presenting a
great degree of variability, with which we have to deal. There are
not several sharply-defined types of coloration; but the extremes are
connected by numerous intermediate forms. The extreme forms, however,
certainly preponderate.
I have never met with Rösel’s light green form; neither was there
a dark green specimen among the twenty-five mentioned, and I
only know this variety from single individuals, found at a former
period. Among the twenty-five caterpillars; all gradations of colour
occurred, from pitchy black to light clay-yellow, and even to an
almost whitish-yellow; some were brownish-black, others of a beautiful
chestnut-brown, and others yellowish brown, dark clay-yellow, or
brownish-red. Out of twenty-one specimens of which the ground-colours
were noted, there were nine black, nine clay-yellow, and three brown;
each of the three groups again showing various minor modifications of
colour. The other colours also varied somewhat. Thus, the “mirrors”
were sometimes white, sometimes strong yellow, and occasionally they
also contained a reddish nucleus.
The variations in the shagreening were especially interesting, inasmuch
as these appeared to have a striking connection with the general
colouring of the caterpillar. Black specimens seldom show such sparse
shagreening as that represented in Pl. V., Fig. 46, but are generally
thickly scattered with large shagreen-dots right up to the dorsal line
(Fig. 47, Pl. VI.), then strikingly resembling the adult larva of _D.
Euphorbiæ_. The light ochreous-yellow individuals, on the other hand,
were sometimes entirely without shagreening (Fig. 48, Pl. VI.), being
smooth, and much resembling the light ochreous-yellow or yellowish-red
caterpillar of _D. Nicæa_ (Fig. 51, Pl. VI.). I have never seen a
caterpillar of _Galii_ which showed traces of the subdorsal line in
the last stage, nor have I ever met with one which possessed a second
row of “mirror” spots; so that retrogression or a sudden advance in
development does not appear to occur.
Of the North African _D. Mauritanica_, which likewise belongs to the
_Galii_ group, I have not been able to obtain specimens or figures
of the younger stages. The adult caterpillar is very similar to that
of _Euphorbiæ_, but differs in the absence of the second row of
ring-spots. For this reason it must be regarded as a retarded form at
an older stage of phyletic development.