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to be dogmatising when one really does not mean it. Perhaps the
subtlety in the working of Nature in this direction has led so many


to take interest in the subject since the publication of Darwin's theory
of " natural selection," but whether this be so or not, it is beyond
question that the study of variation has become the favourite hobby
of a large percentage of entomologists.

First and foremost of the causes which tend to develop variation,
my own observation places " natural selection." But " natural selection "
is based on such a complex combination of circumstances that it is
perhaps advisable to take some of these into consideration, isolating
each particular factor as much as possible, but bearing in mind, that
whilst each factor is working in its own particular groove towards a
certain end, it is modified in every possible way by other factors, the
sum total producing the final effect as seen in the varying character of
our insects, and which we term "natural selection." Meteorological
causes appear to be the most direct active factors in the production of
variation, and inaseries of papers entitled "Melanism and Melanochroism
in British Lepidoptera " which I am contributing to the pages of
' The Entomologist's Record and Journal of Variation,' I am working
out what appear to me to be the chief active agents in the production
of this particular form of variation, and at the same time, I have
attempted to correlate the different suggested causes with each other
nnd with " natural selection." I have also freely criticised previously-
formed theories and attempted to prove or disprove them by the ma-
terial we now have at hand. Although meteorological causes appear
to me to be the more or less active agents in producing variation ;
there can be but little doubt that heredity, disease, food, &c., each adds
its share towards producing the sum total of variation. We will
therefore, now look briefly at each of these probable causes.

That " natural selection " has a very great deal to do with varia-
tion, no one who has made observations on the subject can doubt.
Among the species in the group that we are considering, some striking
examples occur. Take for instance the imagines of the Bryophilidce,
clothed in various shades of green, grey and yellow, with black or
reddish marks in the various species. These assimilate so closely to
the lichens on which the larva? feed, that only a trained eye detects
them resting in their chosen habitation, on the stone walls where they
occur. Different walls have variously coloured lichens growing on
them, and it is found that the environment determines the prevailing
colour of the species in a given locality. The greyer the lichens on
the wall, the greyer will be BryopJiila glandifera, and the greener the
lichens, the greener will be the moth. Hence on the former walls,
var. par will preponderate, on the latter, typical glandifera. Certain walls
in Deal are covered with yellow lichens and there Bryophila perla var.
flavescens occurs, whilst on the old dark granite walls, and on the
dark damp walls of the west coast we find var. svffusa, and so on with
the different varieties in this genus. But in such localities, other forms
will, of course, occur with whatever may be the prevailing form ; these
other forms are due without doubt, to hereditary influence, but a large
percentage will be of a characteristic form. The same facts hold good
with the typical form, and with the vars. suffusa and olivacea of Polia
clii. These different forms are found to be prevalent in different
localities, each assimilating in its own particular direction with its own
special surroundings, the white, dark, and greenish forms all respond-


ing most absolutely to their environment. Polia flamcincta, which also
rests on lichen covered walls, offers parallel ranges of variation, and
whilst the prevailing form of this species at Huddersfield is exces-
sively dark with a large percentage of black markings and scarcely a
trace of ochreous, those from Driffield in the same county are
ochreous in colour, and it is of rare occurrence for a single specimen to
be noticed so dark as the Huddersfield specimens. In Somersetshire,
a tendency to a reddish tint prevails, whilst some splendid dark
specimens, darker perhaps than the Huddersfield specimens, which
were captured in Guernsey by Mr. A. J. Hodges, assimilated exactly
to the rocks on which they rested. Again, whilst the specimens viEpunda
lichenea from Plymouth are dark green in colour, mottled with red,
and similar to the Lancashire specimens ; those from Portland (a
locality comparatively near to Plymouth), but obtained from the pale
limestone rocks, are of a pale silvery-white colour with the red and
green reduced to a minimum. Here we see that in distant localities,
similar surroundings produce the same or similar phases of variation,
whilst, given a different environment, a different phase of variation
becomes apparent. The reason of these special forms in special dis-
tricts is easily explained. Those specimens which assimilate most to
their surroundings, escape their many enemies, and hence, year after
year a gradually increasing number of specimens of that particular
form, which most readily assimilates to its surroundings, is developed
and a local race is formed. Turning from those species that rest nor-
mally on lichen-covered rocks and walls, we find among those species
which normally rest on fences, trees, &c., that many, such as Cucultia,
Xylophasia, Axylia, &c., assimilate exactly, to pieces of cut wood, &c.,
but the great mass of our NOCTU^B rest on the ground, and hence the
geological character of a district has much to do with colour. Agrotis
ripce is white, ochreous, reddish, or greyish in ground colour, according
to the sand on which it rests. Agrotis valligera, A. cinerea, A. cursoria,
A. tritici, A. nigricans, &c., also go through various shades of colour,
according to locality, as do various species in other genera. The
genera Leucania, Nonagria and their allies offer a good illustration of
structural variation responding to environment in another direction.
The species of these families sit head downwards, with their wings
closely appressed to the reed, &c., on which the particular species feeds,
and there look exactly like nodes on the stem. Endless other
instances might be cited, but sufficient appear to have been pointed
out, bearing on the general subject of " natural selection," especially if
we consider that all species exhibit some phase, or are modified by it
in a greater or less degree.

Turning now to the causes which accompany or modify the all-
important " natural selection." In all species there appears to be an
inherent tendency to vary if placed under distinctly and decidedly ab-
normal conditions, whatever such conditions may be. The ordinary
normal conditions of a locality tend to produce the normal forms found
in that locality, whilst abnormal conditions develop latent tendencies,
and variation is the result. It follows that if such abnormal conditions
become gradually permanent in any locality and what were previously
abnormal conditions become normal, a permanent change will take
place in the character of the race inhabiting such a locality. That


such an inherent tendency to vary exists is certainly beyond question,
for if it were not present, variation would apparently be an utter im-
possibility. This general hereditary tendency to vary will also be
more or less influenced in any particular brood by the character of the
parent moths ; whilst in seasonally dimorphic species, which, however,
are almost unknown in British NocTiLaa, but which are common among
the DIURNI, GEOMETRY, &c., the different seasonal forms appear to
vary indefinitely inter se, and also to vary towards each other, such
variation being undoubtedly due to heredity.

Of the abnormal conditions mentioned above as tending to produce
variation, those connected with meteorological phenomena undoubtedly
stand first, and of these, moistures appears to me to be by far the most
important, and, in the production of melanic and melanochroic forms
of variation it appears to be the all-important factor, in developing the
inherent tendencies to vary in this direction. Our melanic or melan-
ochroic varieties abound in the most humid districts and become
generally less and less in number as the districts become drier and less
humid. Whether the humidity accompanies a high or low latitude or
high or low altitude, or whether it be produced by nearness to the
sea, by ocean currents (as in the Gulf Stream and Black Current of
Japan), or brought about by excessive condensation by mists, clouds
and fogs, the result appears to be always the same, the increase of
melanic or melanochroic varieties accompanies in a more or less direct
ratio, the areas of greatest humidity. This is not only so in the British
Islands, but the general principle is proven by reference to the fauna
of the Continents of Europe, Asia and North America and to that of New
Zealand, and there is no doubt that the theory is of general application,
subject only to local considerations and explicable disturbing causes.
Among our own extreme melanic forms, some of the most striking
are Xylophasia polyodon vars. infuscata and nigra, Bisulcia ligustri var.
nigra, Aparnea didyma vars. nigra, lugens, leucostigma and albistigma,
Miana strigilis vars. fasciata and cethiops, whilst Agrotis lunigera, A.
cinerea, A. corticea, A. segetum, A. nigricans, and A. pyrophila, have each
an absolutely black form. Epunda viminalis var. obscura from York-
shire is, in its extreme forms, perfectly black ; Dianthcecia conspersa
from the Shetlands, Hebrides and West Coast of Great Britain, Epunda
lutulenta from the West Coast of Ireland and Dianthcecia ccesia from Ire-
land and the Isle of Man also offer striking examples of intense melanic
variation, when compared with the normal European forms. These are all
extreme in the development of their melanic tendencies, but a very
large number of other species have similar melanochroic tendencies
developed in a lesser degree. Although moisture appears to act so
strongly in the development of these melanochroic tendencies, it un-
doubtedly obtains its greatest power by combination with the generally
applicable and broad features of "natural selection."

It may be well here to point out that Lord Walsingham in his
Presidential Address to the Fellows of the Entomological Society of
London, January 1891, pointed out that moist areas are frequently
such as exclude a large proportion of the sun's rays, and that, there-
fore, the lessened number of chemical rays may tend to produce
melanism. This phase of the subject is fully dealt with in the
* Entomologist's Record and Journal of Variation/ vol, ii., No. 1, pp. 4-7.


Next to moisture, heat, and cold, must be considered the most
important factors in producing variation. All excessively cold areas,
if not subjected to the primary influence of humidity, appear to produce
pallid varieties with ill-developed and suffused markings. Lord
Walsingham, in his Presidential address to the Yorkshire Naturalists'
Union, 1885, referred to the melanic tendencies of high latitudes as of
common occurrence. This was pointed out in * The Entomologist's
Record,' vol. i., pp. 232-233, as an error, and it was shown
that insects from such latitudes did not produce insects which
were generally melanic, but on the contrary more pallid varieties,
and that melanism rarely occurred in high latitudes unless
accompanied by excessive moisture. This was acknowledged
by Lord Walsingham in his Presidential address to the Fellows
of the Entomological Society of London, 1890, when he stated
that he had in mind the general suffusion of markings which species
from such latitudes undergo, rather than actual melanism. For a long
time, cold was considered as the prevailing factor in the development
of melanic forms, the idea probably originating in the fact that most of
the known Alpine forms tended to be melanic ; but there appears to be
but little doubt now, that the melanism of high altitudes is due to mois-
ture rather than cold, since cold apart from moisture, as I have already
pointed out, appears totally unable to develop melanic forms, as the
almost entire absence of this tendency in the lepidoptera of the cold
icy plains of the Old and New Worlds abundantly testifies.

Whilst cold apparently tends to produce pallid ill-marked speci-
mens, heat on the other hand tends to produce brilliantly coloured and
well-marked ones, and we find that almost all our species, having a
wide geographical range, become gradually brighter as we pass from
high latitudes towards the tropics. Cold, too, by delaying larval and
pupal existence is supposed to have an effect in the direction of dar-
kening the colour of lepidoptera, whilst heat is assumed to have an
opposite effect. In the present state of our knowledge, however, it is
difficult to say that this is, or is not so, but Nature, in those polar dis-
tricts, where larval and pupal existence is frequently delayed, pro-
duces as I have already pointed out, rather pallid than dark insects.

Cases are on record in which disease undoubtedly appears to have
caused variation, and there is but little doubt that this is frequently
the case. Every entomologist who has bred lepidoptera largely, knows
that crippled specimens frequently vary in a remarkable manner from
the type. One of the most remarkable examples of this kind that I
have seen among the NOCTU^E is a specimen (previously referred to) of
Orthosia upsilon, belonging to Mr. A. Robinson of Brettanby Manor,
Darlington. This example accompanying a deformity in shape,
exhibits a complete variation in markings, the typical markings being
practically absent, and the specimen being characterised by a series
of longitudinal black marks, in connexion with disease, Dr. T. A.
Chapman of Hereford records in " The Entomologist's Record,' &c.,
vol. i., pp. 271-272, a brood of Cuspidia alni, which all varied more
or less from the normal form, chiefly in the direction of losing
their stigmata, and darkening of ground colour. This brood came
from a race, which was interbred for some time, and during the
time that they interbred freely, the specimens were normal, but the pro-


duction of these varieties was accompanied by a failure to produce
fertile eggs. Dr. Chapman connected it with a change of constitution
and did not consider it necessarily the result of disease.

Food is another factor in producing variation, but it is doubtful
whether direct phy tophagic varieties are ever anything but variations in
size. With plenty of succulent and nutritious food, lepidoptera attain a
large size and it is a common occurrence to find races of the same species,
of different sizes, living in localities comparatively near to each other; one
race, living on more succulent food, of large size, the other, living on
less succulent or less nutritious food, of small size. This is especially
noticeable in certain GEOMETRY as Hypsipetes elutata, Cidaria testata,
Eupithecia satyrata and its var. callunaria and many others. Among
the NOCTUJE, I cannot point to a striking example in this direction,
although undoubtedly such exist, and in confinement if larvae be kept
short of food, dwarfs are the natural result. Generally speaking, the
larger races of such species as these, appear to be more clearly marked,
but this I do not consider in any way due to food, but to the combined
influences of " natural selection " and to the fact that the dark mark-
ings on the smaller moths, are, as it were, placed more closely together
and thus obscure more completely the (generally) paler ground colour.
As all the larger races of the species mentioned feed on bushes, shrubs,
willow, &c.,and the smaller ones on low-growing plants (Vaccmmm), it
can readily be seen that the surroundings of these races are very
different, and the influence of "natural selection" would be correspond-
ingly large.

In an introduction of this kind, anything like an exhaustive essay
would undoubtedly be out of place, but I think sufficient has been
written to show that the phases of variation in our British NocTU-as are
many and striking, that the causes of these are as yet most imperfectly
known and exceedingly complex in their character, and that a large
field is open to scientific workers in this direction as the systematic
classification of the material that we have continually coming to hand
is worked into a more definite form.


Class : NOCTILE, Linn.


1. Family : Cymatophoridce, H.S., Noctuo-Bombycidce, Gn.

COMPAKED with some of the families we shall have to consider
later on in the NOCTILZE, this family does not appear to be
subject to a very great deal of variation, and, when it occurs,
is generally produced by the transverse lines crossing the anterior
wings, coalescing and forming continuous bands. In some cases, the
ground colour is variable, and there is also a tendency in some
species derasa, ocularis and flamcornis to suffusion with red colour.
The difference in the size of the stigmata, and the difference in dis-
tance between the transverse lines before and beyond the stigmata, is
very noticeable in some species. In this family, we rarely get striking
examples of the melanic forms which are so commonly found in other
families, although some of the species have a tendency in that direction,
notably specimens of duplaris (both var. obscura and the type) and
diluta var. nubilata. Flavicornis offers, perhaps, the widest range of
variation, varying from a pale yellowish green to dark-grey in some
specimens, while others are grandly tinged with rosy-purple.

Gonophora, Brd., derasa, L.

This beautiful species is very invariable in Britain. I have,
indeed, never seen a British specimen worth alluding to as a variety.
There are, however, distinct forms on the Continent, one of which is
darker than the type, the other distinctly tinged with purple. The
Linnsean description is as follows : " Noctua spirilinguis cristata :
alis deflexis supra antice decor ticatis." " Antennas et lingua ferruginea.
Alas superiores griseo undulatae sed ad marginem inter iorem, antice,
area per alam extenditur triangularis cinerea, ac si esset decorticata
(tecta tamen est), qua ab omnibus distinguitur. Linea alba alam de-
nudatam cingit ; striga alba ad marginem posticum alaa ; albido ad
marginem inferiorem alee. Inferiores alas fuscescentes ; macula nulla
obscura in paginis inferioribus. Abdomen densiori lana albida
vestitum " ('Systema Naturae', p. 851). Of this description Guen^e
says : " Linne must have seen worn specimens of this species, when
he said : ' Area per alam extenditur cinerea triangularis, perinde ac
si esset decorticata (tecta tamen est) qua ab omnibus distinguitur.' We


only see the median space more denuded of scales than the rest of the
wing " (' Noctuelles,' vol. v., p 12). In my opinion Linnaeus is per-
fectly correct, and Guenee wrong ; unless, indeed, the specimens
under the notice of Guene'e were different to our British specimens.
The following varieties are I believe unknown in Britain :

a. var. intermedia, Brem. This variety is of an ashy grey colour
(" cinerascens," Staudinger), and is only recorded, so far, from the
eastern part of Dr. Staudinger's European fauna district, Amur and
Armenia. Dr. Staudinger thinks this variety may be the gloriosa of
Guenee's ' Noctuelles,' v., p. 12, which is considered by Guenee as a
variety of Thyatyra abrasa, an American species.

P. var. derasoides, Dobree. Of this variety Mr. Dobree writes
me : " A very distinct variety, of a purple shade of grey, and no
trace of white. From the Amur district " (in litt.).

Thyatyra, Och., batis, L.

This pretty insect is another invariable species in Britain, the
coalescence of the two rosy spots near the apex of the wing, which
occasionally takes place, being the only noticeable feature. The
Linnasan description is as follows : "Noctua spirilinguis Ia3vis, alis
depressis : superioribus fuscis, maculis simul quinque albidis :
inferioribus albis." " Maculae orbiculares albide medio fusco, sparsse,
magnas " (< Systema Nature', p. 836, No. 97). It seems very strange
that the Linnsean description makes no note of the rosy colour of the
spots which are so characteristic of this species, but I have an Irish
specimen without a trace of this colour. I would draw attention,
however, to some little variation in the development of the cell on
the outer margin of the wing directly above the large spot in the
anal angle, and also to the fact that, between the apical spot and spot
at anal angle, an obsolete series of dots often shews some traces of
development ; I have specimens with none, one, two, and three of
these dots. I should be pleased to learn of specimens with a complete
series, as undoubtedly some such exist.

a. var. juncta, mihi. The anterior wings with all the character-
istics of the type, but with the two rosy spots at the upper part of the
wing towards the costa joined together. The variety is taken with
the type.

P. var. mexicana, Hy. Edw. Mr. T. D. A. Cockerell (' Entomolo-
gist,' vol. xxii., pp. 306-307) thus writes : " In looking over some
vols. of ' Papilio,' I came across (vol. iv., Jan. 1884, pp. 16-17), the
description of a new variety of T. batis named as above, which I
quote, as it is omitted from Mr. Tutt's valuable paper (Entom. xxi.,
p. 46), and is presumably unknown to British lepidopterists. It
differs from the European form by its larger size, much darker
ground-colour of the wings, both primaries and secondaries, and by
the pinkish spots having a larger and darker internal shade. The
ground-colour of the primaries is rich dark olive-brown ; the
secondaries the same colour, with fainter median band, and a little
lighter shade at the base. Exp. wings 44 mm. This moth was taken in
Mexico by Mr. Wm. Schaus, Jr."


Cymatophora, Tr., octdaris, L.

The Linnrean description of this species is as follows : Noctua
elinguis lasvis, alis cinereis fascia pallidiore lineis nigris terminata
ocelloque notata." " Corpus mediaa magnitudinis, cinereum, non
cristatum. Alae superiores cinereaa, in medio fascia, in duas areas
divisse: Fascia albidior, antice posticeque linea nigra, terminata,
versus latera exteriora dilatata, ibique ocello parvo albo, pupilla nigra
notata ; in area anteriore punctum nigrum ; ad apicem alas lineola
atra ; margo alas posticus lineola nigra. Alas inferiores, omnesque
subtus albidaa absque area et puncto " (' Systema Nature', p. 837, No.
100). Guenee says : " The name (ocularis) was suggested to Linnaaus
by the resemblance which the reniform stigma offers to a pair of
spectacles " (' Noctuelles,' vol. v., p. 19). The above description
agrees with our ordinary form very well except with regard to the
stigmata which are usually joined and form a figure 80, the 8 being the
reniform the 0, the orbicular. It is remarkable that Linnasus should
name an insect on the peculiar character of the reniform, and then en-
tirely leave it out of his description, as he seems to have done. This
discrepancy has led to the use of Hiibner's name octogesima by almost
all our Continental entomologists. I have kept the Linnaean name,
but have added Hiibner's name below for our common form. This
species, too, is one in which a beautiful rosy tinge is found in some

o var. octogesima, Hb. = octogena, Esp. Hiibner's octogesima (fig.
209) is a good figure of the ordinary form captured on the Continent,
although small. It has the anterior wings of a grey colour with a
delicate rosy tinge, especially at the basal and costal areas of the wing,
with two double abbreviated basal lines having a dot at the extremity
of each ; a complete line just before orbicular ; stigmata pale, forming
the mark 80, with their centres black, transverse shade between
stigmata, another through reniform, whilst a third is found directly
beyond reniform ; hind margin a very little darker than ground colour.
Hind wings dark grey, lunule distinct, base paler. Our specimens are
somewhat darker in ground colour, but otherwise agree exactly with
Hiibner's octogesima. Esper's diagnosis of octogena also agrees with
this variety : " Alis superioribus cinereo-rufescentibus, strigis undatis,

Online LibraryJames William TuttThe British noctuæ and their varieties (Volume 1) → online text (page 2 of 24)