B betularia 1901

Biston betularia, Peppered Moth, from G T Porritt collection, (in Tolson Memorial Museum) showing typical form and melanic variation, from Crosland Hall, South Crosland, 1901.


This article was written in 2007 and submitted for publication to the Naturalist, the journal of the Yorkshire Naturalists Union ( of which I am a member) but was rejected.  Some of the reasons for that are set out in the appendix which presents the comments of the peer reviewer, Prof. Laurence Cook, an authority on the topic. Whether it is suitable for the Naturalist I leave readers to make up their own mind.  However, three years later the journal did publish a paper by Geoffrey  Fryer, entitled ‘George Taylor Porritt’s 19th and early 20th century observations on industrial pollution in moths in South West Yorkshire, and their continued relevance to a long running debate. ‘ (The Naturalist, No. 1075, Vol. 135 Oct-Dec 2010). He followed this up with ‘Another early challenge to the ‘orthodox’ interpretation of industrial melanism in moths, posed by some forgotten observations of Ben Morley in 1911’ (The Naturalist August 2012,Volume 137, Number 1080)

In the acknowledgements of the first paper Geoffrey Fryer kindly wrote: ‘While investigating early Huddersfield naturalists, Alan Brooke unearthed Porritt’s York lecture and made notes on it, which I saw in 2007. I hope he feels that this paper goes some way to rectifying the neglect he recognised at that time’.   

His paper certainly does more justice to Porritt than I achieve in this article, which is  based on the notes he refers to.  His knowledge of moth ethology and genetics are far beyond my capabilities and he sets the work of Porritt in a scientific context which seriously, I would say fatally, undermines the orthodox view of ‘industrial melanism’ in the Peppered Moth,  an icon for evolutionary biologists as an example of natural selection in action.

Laurence Cook, who severely mauled my article, also criticised Geoffrey Fryer in the Linnaean, ‘Correspondence: Fryer’s new look at industrial melanism in moths – a comment’,  (VOLUME 29 · NUMBER 1 · APRIL 2013), while Fryer replied in a paper entitled, ‘How should the history of industrial melanism be interpreted’  in the next issue (VOLUME 29 · NUMBER 2 · OCTOBER 2013). One of the assertions I made in my original article for the Naturalist, which Prof Cook took exception to, was to describe the debate on the Peppered Moth as still ‘raging’.  It wasn’t, according to Prof Cook. The issue was resolved, was part of scientific orthodoxy and was beyond criticism.  Indeed in a paper published in Heredity in 2013 Cook does not even cite Fryer’s Naturalist research and Porritt only gets a reluctant mention.  (L M Cook and I J Saccheri  ‘The peppered moth and industrial melanism: evolution of a natural selection case study’  Heredity (Edinb). 2013 Mar; 110(3): 207–212: )     However, Fryer’s paper and the subsequent debate shows that the matter is not closed and that there are sound scientific reasons for questioning industrial melanism which do not emanate from creationists.

Porritt and other Huddersfield naturalists do have a contribution to this discussion from beyond the grave.  I hope that this article, and the other papers I have referred to, ‘rectify the neglect’ these dedicated, self taught ‘amateurs’ have suffered at the hands of modern academia. It also emphasizes the scientific importance of the lepidoptera collections of Porritt and Morely in the Tolson Memorial Museum at Ravensknowle and the terrible loss to the area the proposed closure of this museum would entail.


On 4 February 1922, Seth Lister Mosley (1848-1929) in his Huddersfield Examiner column ‘Nature Around Huddersfield’, described the increase of melanism in moths in SW Yorkshire and Lancashire.  His local pride, boosted by his curatorship of the town’s first municipal museum at Ravensknowle, encouraged him to claim,

‘As Huddersfield was one of the first places, if not the first place where this melanism appeared and as it has developed and affected more species in this district than perhaps any other, a very good collection of insects illustrating this curious fact ought to be in our local museum for reference, because it is certain that future students of this phenomenon will turn to Huddersfield as the place of all places to seek an explanation.’  [1](1)

Although Huddersfield can not claim the crown for the origin of melanism, (in most accounts the earliest occurrence is now attributed to the Manchester area, where it was observed in the Peppered Moth (Amphydasis betularia / Biston betularia) around 1848), Mosley’s claim that the district made a special contribution to the understanding of the phenomenon does have merit.  This is due both to his own work and that of other local naturalists, particularly George Taylor Porritt (1848-1927) and Ben Morley (1872-1932).

The interest in melanism grew out of the wider interest in variation, both as a scientific study essential for accurate classification and through the desire of collectors to obtain a full ‘series’ of differently coloured and patterned specimens of each species in their cabinets.  In November 1870, at a Huddersfield Naturalists’ Society discussion on the cause of variation in lepidoptera, Porritt advocated the theory that, in many cases, it was the result of disease, while other members attributed it to the effect of different foods on larvae.  Aberration from type was therefore regarded as a characteristic acquired from the environment and not of any adaptive value.(2) [2]


In 1891 James. William. Tutt (1858-1911) collated a mass of data on variation in one group of moths for the first volume of his ‘The British Noctuae and their Varieties’.  Mosley and, to a greater extent, Porritt, were among the Yorkshire naturalists who provided him with information and specimens.  Tutt also proposed explanations for the phenomenon, clearly setting out his Darwinian stall, ‘First and foremost of the causes which tend to develop variation, my own observation places “natural selection” ’. adding the caveat that this depended on ‘a complex combination of circumstances’ which had to be taken into account,  ‘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.’   Of the meteorological factors, humidity ‘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 melanochroic varieties abound in the most humid districts and become generally less and less in number as the districts become drier and less humid’.

Moisture may have set the environmental stage, but it was not the main actor since ‘ it undoubtedly obtains its greatest power by combination with the generally applicable and broad features of “natural selection”.’  He described this at work in increasing the frequency of variations that matched the colour of the surfaces on which they rested,  ‘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’.

However, one factor he did not specifically refer to was the effect of industrial pollution in the manufacturing districts.   This was despite the fact he had recently described this in a paper in the ‘Entomologists Recorder and Journal of Variation’ (I:55-56), (published along with other papers as a booklet ‘Melanism & Melanochroism in British Lepidoptera’  later that year).  In the first volume of British Noctuae he referred to one species which could have illustrated this, based, moreover, on a specimen provided by Porritt.

Describing the Large Ranunculus (Polia flavocinta/Antitype flavocinta ), one of the moths which exhibited a range of variations according to the surfaces on which it rested,  he pointed out that ‘the prevailing form of this species at Huddersfield is excessively dark with a large percentage of black markings and scarcely a trace of ochreous’,  in contrast to those at  Driffield which rarely showed any melanic features.  However, while pointing out that a dark type also was found on naturally black rocks in Guernsey, he did not venture the explanation that pollution was a factor in the colouration of Huddersfield’s walls.

That he was well aware of this is apparent from his description of a related species with similar habits, the Grey chi  (Polia chi / Antitype chi), published in Volume III the following year.  Quoting Charles Goulding Barrett (1836-1904) he described the appearance of P. chi, ‘… on the slopes of the Pennine hills, between Oldham and  Huddersfield, where the original grey or whitish colour of the stone walls has become totally changed by the constant action of smoke from the cotton mills of the large towns, and the woollen mills of the  villages, this moth becomes so conspicuous that it may be seen fifty yards away, and is indeed more noticeable than the wall itself.’  Tutt speculated that Barrett may have in fact merely not seen the melanic form, since in the Huddersfield area Porritt had just discovered specimens which were exhibited at the meeting of the Entomological. Society in London, on 10 February 1892. (3) [3] If Tutt intended this species to be an example of melanism related to the effects of industrial pollution it was not a felicitous choice, since the melanic form did not become dominant even in the manufacturing districts.(4)[4]

In his ‘Melanism and Melanochroism…’ booklet, however, he explicitly uses two other species recorded by Porritt in the Huddersfield area to show industrial melanism at work, the Mottled Beauty (Boarmia repandata/Alcis repandata) and the Dotted Border (Hybernia progemmaria/ marginaria/Erannis marginaria),. describing the latter as ‘excessively dark from the Huddersfield locality.’  Porritt had described melanism in H progemmaria and Diurnea fagella in the Entomologists Monthly Magazine in July 1886. Tutt’s reliance on Porritt as a source of information is also acknowledged in the reference to the rainfall figure for West Yorkshire. (5)[5]

Four years later, in his ‘British Moths’, Tutt, in an intentionally pedagogic account which was to become the model of industrial melanism, established the Peppered Moth as the classic example of the phenomenon.  Describing the blackening of surfaces by soot and smoke around the manufacturing towns he outlined how this gave an advantage to the ‘negro’ form of the moth, better camouflaged against bird predation.  ‘This blackening we call “melanism” and the Peppered Moth is by no means the only kind of insect in which this melanic change has been brought about in recent times.  Many others are becoming jet black in these districts, and some of the Yorkshire naturalists have made many remarkable discoveries in this direction.’ No doubt Porritt was one of those he had in mind.  However, Tutt concluded by emphasising that this form of melanism was only relevant to those species with the habit of hiding on surfaces ‘blackened by smoke and damp.’ (6)[6]

B betularia June 2007

Melanic (carbonaria) and typical form of B betularia ‘captured’ 2007 at Magdale, only about a mile from Crosland Hall.


A decade later Porritt presented the first comprehensive account of the manifestation of melanism in species occurring in the Huddersfield district in his paper ‘Melanism in Yorkshire Lepidoptera’ delivered to the Zoology section of the British Association, meeting at York in 1906.  There were, by now, over 30 species in Yorkshire exhibiting melanic variation and yet others showing forms darker than the type.  About eight or nine had always been evidently dark and it was not known if they originated from a paler type.  Although the Peppered Moth was the earliest example of developing melanism noticed by lepidopterists, it was not until c.1880 that an increase in black forms (then known as var doubledayria) was apparent in West Yorkshire. Even in his own collecting experience, (he had started as a teenager), it was considered fortunate to get a black specimen, but, by 1906, the original form had been practically ousted in the south West Riding and he had obtained only one pale specimen in Huddersfield in the previous decade.  He noted that the development had occurred suddenly without intermediate stages, the only difference being that the northern type was more heavily peppered, with a less discernible pattern than the southern. (7)[7]

Around the same time as the increase in melanism was observed in the Peppered Moth it was noticed in several other species.  Porritt stated in 1906 that this was about 25 years previously, which corresponds with Mosley’s account in his 1922 article of its appearance around 40 years ago.  Both were assiduous collectors and recorders and their agreement firmly dates the noticeable increase of melanism in the district to the early 1880s.  However this is not the same as saying that melanism originated from this time. Porritt described the Mottled Beauty, (Boarmia repandata /Alcis repandata), as one of the species which increasingly showed a melanic tendency.  In 1887 in a wood at Netherton, near Huddersfield , he collected dark specimens ‘freely’ on pine trunks, from which he bred a perfectly melanic specimen ‘as black as ink’ and different from any previously known to him, as well as a large number of other dark brown ones.  By 1906 the black form was common in several woods in S W Yorkshire.  However, he conceded that it, ‘may have been common long before we noticed it.’ Two black specimens were found in the store box of a dead collector in Huddersfield, which had been taken perhaps as early as the 1850s. His collection cabinet had all the ordinary series of the moth, but for some reason he had confined the melanic type to a box. (8)[8]

In the case of the Mottled Grey, (Larentia multistrigaria / Colostygia multistrigaria), despite being abundant, it was not until 1895 that a dark specimen was observed.  This also must have existed undetected in the area previously since Henry Doubleday (1808-1875) wrote to James Varley of Almondbury (1817-1883) for eggs from the moth and bred a black specimen, which remained in his collection in Bethnal Green museum.  Porritt concluded, ‘Here we have another instance of the latent tendency to melanism which in this species was not really developed until over thirty years afterwards.’  By 1905 Ben Morley was recording that it was abundant around Skelmanthorpe, including many of melanic variety nubilata so that it appeared that this moth, ‘will soon be a black race about there’.(9) [9] The trend appeared confirmed by Porritt in a breeding experiment which produced around 70 specimens of which only five or six were pale. However, this species did not support the standard explanation for the increase of melanism – that the paler type was more vulnerable to bird predation –  since it did not rest on tree trunks or walls  during the day, but hid in grass and the herbage of its food plant Heath Bedstraw (Galium saxatile), where melanic colour change was of no advantage. (10) [10]


Phigalia pilosaria, Pale Brindled Beauty, melanic type, Magdale, 2007.

One species which did rest on the trunks of oaks and other trees was the Pale Brindled Beauty (Phigalia pilosaria/Phigalia pedaria). Prior to 1886 black (wingless) females were known according to Porritt, but from that time it was noticed that males were rapidly becoming darker.  The moth was common in the district and was often the first species to appear. In 1901 Ben Morley recorded that the first capture of year in the Skelmanthorpe area was a ‘lead coloured’ form of the moth.  It was again very common in 1905, when Morley again reported a black specimen which contrasted with another capture from Deffer Wood, which was ‘the palest he has ever seen’(11)[11]. A report on the moth in the Examiner natural history column of 8 May 1909 (probably by Mosley), described the moth’s widespread distribution in local woods, commenting that the local species showed a tendency to melanic variation. In Deffer Wood it remained common until 1913 when Morley recorded a poor emergence of the species, becoming ‘a rarity’ the following year.(12)[12]  The population must have been hit in other locations since Mosley described it in 1917 as  formerly abundant, although still fairly common in Storthes Hall Wood.  The dark variety was now the more common.(13)[13] The following February Porritt described it as ‘not uncommon, ‘two thirds of the specimens, in my experience, being of the melanic form.’.(14)[14] In January 1919, W.E.L Wattam reported that the moth was ‘extremely common’ in Mollicar Wood and although the pale form predominated black ones were ‘not uncommon’. A year later, however, on 25 January, in the same wood, only three out of 19 he saw were melanic.(15)[15]  Melanism in this moth was widely considered a classic example of an industrial origin, although this theory was contested in 1919 by E P Butterfield of Wilsden who claimed that on the oaks in Bingley Wood it was the dark specimens which were the most visible and even these did not appear to be eaten by birds (16)[16].

The Dotted Border (Hybernia progemmaria/marginaria/Erannis marginaria) was another species in which black varieties of the flightless, (but not entirely wingless) female were known before 1886.  Tutt, in his ‘British Moths’ (1896) referred to the variety fuscata which was found in the Huddersfield and Birmingham areas and had an ‘almost entirely black’ ground colour. By 1901 Morley reported that in Skelmanthorpe  it ‘swarmed as usual, and after careful observation it was concluded that about one-tenth of their numbers were the variety fuscata.’  According to South (1961) ‘the blackish’ . fuscata variety was originally  confined to northern England but occurred later in Surrey and Essex.’.

Porritt, also carried out experiments with the Scalloped Hazel (Odontoptera bidentata/Gonodontis bidentata) in 1904 breeding from a black specimen six melanics out of nine.  A larger brood the following year produced  75% melanic and from the   ‘considerable number’ bred in 1906 an even greater percentage emerged melanic.  He concluded, ‘Three generations thus produced an almost entirely black race, which proves that the hereditary principle towards melanism must be remarkably strong’. However, the melanic form was not recorded around Skelmanthorpe until 1925. (17) [17]

From around 1899, when it was first noticed by Morley in the Skelmanthorpe area, melanism also increased in the Dark Arches moth (Xylophasia polydon/Apamea monoglypha). In 1905 it was reported that black specimens ‘are more frequent’. and in 1906 he noted that it, ‘has afforded much interest in this district of recent years…Always an abundant species, and forcing itself upon one’s notice so much by coming to “sugar” so freely. Since it was first noticed, ‘every year the black ones have been more in evidence. During the last season it may be said to have become quite common…’  Intermediate forms were also common, ‘but melanism is no doubt developing very rapidly, in this immediate locality, at any rate in this species.’(18)[18]


Agrotis agathina, Heath Rustic, speciman of melanic type first noticed in his area by Ben Morley in 1905. This specimen bred from larva.

The melanic form of another species became specifically associated with the environs of Skelmanthorpe.  The larvae of the Heath Rustic (Agrotis agathina/ Amathes agathina) were first taken in 1905, on a moor three miles from the village.  Morley bred 15 moths which Porritt pointed out were of a much darker form than in the rest of the country. According to Porritt the moor had not previously been worked so it was not known how long the dark form had been present.   With a tantalising omission of detail South states, ‘The very melanic (ab. scopariae Milliere) come chiefly from the Skelmanthorpe district)’. (19) [19]


Polia chi, Grey Chi Moth, Digley, August, 2007. Porritt observed that ‘it can be readily observed from a great distance’ on dark stones and yet the melanic form did not become predominant.

One moth which exhibited a great range of variation and which, from its habit of resting on walls in daytime, should have favoured the melanic type was the Grey Chi, Polia chi / Antitype chi. We have seen above how Tutt acknowledged Porritt as the discoverer of a melanic form in 1891. Porritt described the moth in 1906 as showing a gradually darkening from almost white to a dark slate colour. The melanic form was a case of ‘specifically local melanism’ occurring only around Huddersfield.  However, ‘on the equally black, or even blacker walls bordering our high moors, only half a dozen or so miles away, almost all the specimens are of the palest form and can be readily seen from a considerable distance’ – thus confirming Barrett’s earlier observation which Tutt had regarded with some scepticism.  Porritt’s own collection contained 100 examples of local Polia chi which include all the known variations from light grey to almost black.  In 1908, Morley reported that it was ‘exceedingly common and was perhaps the most interesting species of the year in the Skelmanthorpe district.  Its habit of sitting on the walls in the daytime gives the collector fine chances of taking his choice without much trouble…’   The variety olivacea and a very heavily marked form were common, while ‘Another form frequently found has the wings of a drab colour with all the markings obliterated, except the black chi mark which is very small and well defined. It is a very fine and beautiful form probably of recent development and the most decided variation from the type we have noticed in the Skelmanthorpe neighbourhood.’ (20)[20]. On 7 August 1911 Charles Mosley saw seven on a wall at Fixby, three of which he photographed for the Naturalist, showing their high visibility .  Three were the olivacea form, none were melanic. Porritt speculated that this might be one species in which melanism was affected by the climate since dark forms appeared commoner in dull wet years.(21)[21]

Melanism continued to be detected in new species. In 1925 Porritt reported that the Broom moth (Hadena pisi/Ceramica pisi) was more abundant on Bilberry at Royd Edge, near Meltham, than ever known previously.  He collected 11 larvae from different parts of the moor from which he bred four moths in 1926, ‘all of an almost uniformly dark purplish brown colour, with the exception of the usual yellow subterminal band..  I had never seen any like them….’  The only one similar was taken from Rannoch many years previously, but these specimens were much darker than the variety, scotica.    He exhibited them at the YNU Entomological Section annual meeting in Leeds that year.  The larvae of the Common Vapourer (Orgyia antiqua) were also prolific in the same place at the same time and moths appeared in large numbers, including a large number of the dark variety  confines. (22)  [22]

It is evident from the fact that since such different species of moths, with a wide range of  behaviour and occupying diverse habitats, showed an increase in melanism, no single, catch-all model of industrial melanism could be applied.  Ben Morley concluded that, ‘At present it almost seems impossible to arrive at any satisfactory conclusion as to what agent or agencies are in force causing the variations…Not only is the melanic tendency remarkably well developed in many species locally, but of recent years other species not affected by melanism are actually showing a strong tendency to vary in the opposite direction and frequently examples are obtained, the bright colours of which are quite surprising.’(23)[23].

Even more perplexing were the instances where species in the Huddersfield area remained faithful to type, while elsewhere, in places where ‘the smoke theory’ could not be invoked, melanism was apparent.

This Porritt came to refer to as the ‘contradictory anomaly’.  He contrasted two species which shared the same habitat on the moors around Huddersfield.  The Common Heath  (Fidonia atomaria/Ematurga atomaria) had yielded a black form in 1906 at Harden Clough, and over the following couple of decades showed a gradual increase in melanism so that by 1926 ‘a very considerable percentage in both sexes are brown-black or black, in many without markings, in others practically so, whilst all the males are darker than the typical form…’  In contrast, on Skipworth and Strensall Commons in east Yorkshire, only most ordinary typical forms were evident and ‘… nothing approaching- Melanism has ever been seen there’ (Porritt 1926).

However the Light Knot-grass moth (Acronycta menyanthidis/Apatele menyanthidis) which frequented the same moors as the Common Heath showed no sign of melanism until c. 1920.  Porritt wrote in 1926

‘As I stated in ‘ Yorkshire Lepidoptera,’ the species was “ almost invariably of the palest form we know in Britain, and a black specimen was never seen.” About five years ago a black specimen was found, and since then one or two specimens have, I think, been taken each year, some six or eight in all, and no doubt in the future it will become common. Yet on the heaths at Skipwith near Selby, and at Strensall near York, both districts in which there is comparatively little smoke as compared with here, menyanthidis has, apparently as many years back as anything has been known about it, been so entirely of the black form that the Rev. C. D. Ash (formerly Vicar of Skipwith) tells me that probably not two per cent. of the pale form are to be found there. Mr. Samuel Walker of York also informed me that the same thing obtains at Strensall, and that no specimen is ever seen so pale as the South-west Yorkshire moth’ (Porritt 1926).

Another moorland species which showed no sign of melanism locally was the Northern Spinach moth (Cidaria populata/Lygris populata). However the dark unicolorous form was common at Rannoch and other locations in the Highlands of Scotland, where Porritt had  experience of collecting.  The contrast was stark, ‘ populata occurs in thousands on our moors, but I have never yet seen on them a single specimen showing any sign of Melanism. Yet at Rannoch there is probably as little pollution of the atmosphere by smoke as can be found in any part of Great Britain’.  The  Brown Rustic (Rusina tenebrosa/ Rusina ferruginea) was also  considerably darker at Rannoch than at  Huddersfield, as was the Dark Brocade (Hadena adusta/Eumichtis adusta) . (24) [24]

This ‘contradictory anomaly’ was also exemplified by a moth particularly dear to Porritt’s heart. The  Water Carpet moth  (Cidaria. suffumata/ Lampropteryx suffumata) had a variety named after him, although it was very rare. In 1901 Morley reported that in Skelmanthorpe the moth ‘came out in some numbers, but was unusually true to ordinary form; only one imago of the variety porrittii was taken, and none of the intermediate form’. The change it did display was away from melanism.  Five years later  Morley  described how he had netted a few last spring and when they were pinned in the cabinet,

‘the difference in comparison with others taken on the same hedgerow seven years ago was very striking indeed.  The lighter parts of the wings were more clear and the central band darker.  In the same locality a brighter form than this is frequently taken, and very rarely the extreme (light) form var Porrittii…It may be of interest to note that the dark form piceata , which occurs in some parts in the north of the county, has never been recorded here. One would almost expect to find that the dark form would be the natural variation of the species in this district, where melanism predominates in comparison with other variation…’  (25) [25]

Porritt alluded to this  again in 1926.  Probably half the specimens captured locally were of the ordinary form, but the rest were brighter and paler, with a complete series of  gradation culminating in the black-and-white porrittii.

‘Anything approaching the dark brown unicolorous var. piceata, which is common further north in England and in Scotland, has so far as I know never been seen here, nor have, I believe, our pale forms been seen where the var. piceata occurs’.

The advert for subscribers to save the Porritt collection for the town, following his death in 1927 explained,  ‘The very rare var. porrittii, of which only about a score are known, is represented in this collection by five examples from the Huddersfield District. These specimens were regarded by Mr. Porritt as being the most valuable of his many varieties’(26)[26].  South also names porrittii as occurring only at Huddersfield and the Forest of Dean (27) [27].


Abraxas grossulariata, Magpie Moth, dark variety, nigro-varleyata,bred by Porritt in 1916.

The complexity of the melanism problem was also illustrated by another moth which had a variety named after a local naturalist. In 1864 James Varley raised from larvae a good series of a black bordered variety of the Magpie (Currant) moth  (Abraxas grossulariata) which was named varleyata  by Porritt.  It proved a good money spinner and Varley sold varieties from his breeding stock for £1 each. (28)[28] Porritt described it in 1906 as ‘A very striking almost black form of this abundant and well known moth…’  But it was still as rare as it was 42 years ago, ‘Indeed the variety varleyata, for such it was afterwards named, is today one of the greatest prizes a lepidopterist can obtain’.  The species was extremely variable and Porritt’s own collection eventually had eleven local forms.  This made it very attractive to collectors.  In 1904 J Lee of Bradley Mills produced an ‘extremely beautiful series of Abraxas….’ including peppered, radiate, and yellow moths, while A Kaye of Lindley bred several with success, including varleyata[29](29). Porritt reared a considerable brood in June 1906, every specimen turning out to be a varleyata,  He believed that ‘the hereditary tendency’ was stronger than in any other species he had experimented with.

‘Known more than 40 years ago, [varleyata] is today as rare as it was then, although its heredity tendency is so strong that a brood raised this year from a pair of moths from wild larvae were all of the extreme form, not a single example showing any tendency to revert to the pale ordinary form or to any other than varleyata.’

The form was described by South as occurring in Yorkshire ‘but is mostly reared in captivity from eggs obtained from a wild female in the first place and subsequent pairings’.  He used a specimen borrowed from Porritt’s collection as an illustration. (30).[30]  In 1907 Porritt, describing the breeding of var. varleyata,  also referred to his ‘somewhat extensive experience in breeding melanic forms of other species.’ and the tendency of these, unlike A grossulariata, to show reversion to the type (31)[31].  Tutt, apparently unmindful of his hero Darwin’s own interests, scathingly condemned how this species

‘has been subjected to most wonderful experiments for the purpose of breeding aberrations, extreme forms of which have found a ready sale, and hence, in the name of science, some men have reduced entomology to the level of fancy pigeon and rabbit breeding.  Some almost white, others almost black have been produced, but extreme natural aberrations are not uncommon.’ (32)[32]

However, with the rediscovery of Mendel’s work, such experiments were vindicated and selective breeding contributed to an understanding of how heredity worked to produce variation.  Porritt was able to provide material which enabled H Onslow in 1921 to establish that varleyata depended on an autosomal recessive gene. (33)[33]

Porritt reported in 1910 ‘so much interest is now taken all over the country’, in the moth and Lee, Kaye and himself had bred several varieties including a true melanic one, nigrosparsata, which was unknown in 1906.  Kaye bred this variety again in 1916 when Porritt commented that ‘More than the usual numbers of fine varieties of Abraxas grossulariata have been reared in the district’. (34)[34] By 1919 he claimed this species represented ‘Perhaps the most recent and most rapid example of melanism in this district…’  The variety  nigrosparsata, had become established in gardens in the town, in one part of the district a ‘considerable percentage’ being of this form, including some almost black. At the time Porritt did not regard this as evidence for the ‘smoke theory’, since ‘nigrosparsata only occurs freely on one side of the town, other parts of it, apparently quite, or still more smoky, producing scarcely any of it, though the moth is equally abundant there.’ (Porritt, 1919). But by the end of the following year he reported that the moth  ‘seems to have practically disappeared from the gardens of the West Riding during the past two years.’(35)[35]  It was not until 1926 that he could write, ‘Now it is becoming plentiful again, but nigrosparsata is as yet only got in very casual specimens, and it will apparently be some years before it regains its former strength’.   He had also modified his views slightly, ‘I do believe there is some connection between smoke and melanism.’ [GTP’s emphasis], since nigrosparsata was found only in town gardens and not in the surrounding countryside.  However, he did not believe it was related to melanism as protection from predation, ‘a theory to which I could never subscribe.’  In the case of the Magpie moth this was easy to substantiate. At Porritt’s 1906 lecture to the BA it had been pointed out by Professor Edward Bagnall Poulton (1856-1943) that there was no pressure for the dark varleyata population to increase, since neither birds nor animals touched the moth at any stage of its life-cycle.  It is now known the moth has an unpleasant taste and its colours serve more as a warning deterrent than for crypsis.  This being the case, melanism could even be disadvantageous.


Abraxas grossulariata, Magpie Moth, showing wide range of varieties.

Although to modern researchers the observations made by Porritt and other local naturalists may appear vague and anecdotal, lacking any firm statistical basis, they do reflect a serious questioning of the simplistic attribution of melanism to industrial pollution – a theory which was itself based on the same methodological premises.  In his 1906 paper Porritt emphatically rejected Tutt’s model as an adequate explanation for the phenomenon,

‘in the large manufacturing districts which have a humid atmosphere or heavy rainfall and hence it has been assumed that smoke and moisture aided by natural selection have produced the phenomenon. Mr Tutt has argued the case from this standpoint at great length in his pamphlet “Melanism and Melanochroism in British Lepidoptera”. No doubt it is true that melanism is almost confined to the western side of Britain, that is, the side most influenced by the Gulf Stream and also that it is most prevalent in the manufacturing, and consequently smoky districts of our island.  But if smoke is an essential, how are we to account for the numerous and marked examples of melanism in the Hebrides, the Shetlands and Orkneys, where there is no smoke…’

Porritt, Morley and other field naturalists clearly knew that melanism was not confined to the manufacturing areas but occurred in the more rural parts of Yorkshire and the Highlands and Northern Isles of Scotland, which were free of significant pollution.  They also knew that even in the smoke affected areas where melanism was increasing some species showed a contradictory trend.  Porritt was also not convinced of the selective mechanism and in 1906 posed two crucial questions about melanism, ‘Is it really protection ? And from what?’  He dismissed the idea that birds fed on moths, pale or otherwise, resting on tree trunks, ‘My own experience certainly does not warrant any such conclusion’.  Most birds fed on caterpillars and in evolutionary terms eating moths would be, ‘killing the goose which lays the golden eggs.’  The main predators on moths, goatsuckers (nightjars), bats and dragonflies fed on the wing, the first two at night, so melanism would provide little protection.    (36) [36].


One aspect Porritt certainly did not understand was what brought about melanism in the first place ?  He assumed that natural selection would be the result of gradual accumulation of characteristics, not the sudden appearance of melanism he was witnessing. He believed however that heredity alone was sufficient to account for a rapid increase in the melanic population once established.  With our understanding of genetics this is one question we can answer, since we now know that a single allele can produce a melanic phenotype.

In 1919 Porritt entered into a debate in the pages of the Naturalist with E.B Butterfield, of Wilsden concerning melanism, particularly in Phigalia pilosaria.  Butterfield ventured the theory of ‘retarded development’, that it was climatic factors affecting the insect in the pupa which led to melanism in the imago.  The first occurrences of melanism were noted in his neighbourhood only from the 1880s following the winter of 1879-80, which was one of the worse on record and a very cold 1881. He asserted that there was experimental evidence that low temperatures in pupae darkened the scales of lepidopterous insects. Porritt frankly admitted that while disagreeing with the theory he did not have the answer.  ‘Neither I nor anyone else knows any more as to the cause of melanism in Lepidoptera than we did 20 or more years ago and that was practically nothing…’  No single theory accounted for all the examples and he thought that, ‘smoke is one of the most potent causes, but that possibly different causes account for melanism in different districts.’

Butterfield dismissed the ‘smoke theory’, which broke down because dark P. pilosaria were more visible on Oak trees in Bingley Wood and they were not much predated by birds. Indeed, he argued,  since the first melanics had occurred in the 1880s there was now less smoke in district.  Altitude was also a factor since moths such as the Grey Chi suffered more retardation in higher locations, this was also evident in the smaller size of melanics.  Porritt pointed out that melanism was not more marked in mountainous districts.  This might be the case in the proximity of manufacturing districts, but in the Lake District and at Rannoch, where, for example, pale varieties of  the Miller moth (Acronycta leporine) and the Wood Tiger (Chelonia plantaginis var hospita) were abundant ‘I am not arguing that the “smoke theory” covers all cases – it does not: but the “low temperature” theory does so I think even much less, though possibly it does account for some…’  If it was a factor, why had it not occurred when there had been cold late springs before ? It also did not explain why there were far more melanic species on the wing in summer and autumn which were not in the pupal stage in the spring. (37) [37]

Porritt again broached the question of the ‘smoke theory’ in an article on ‘The induction of melanism in the lepidoptera and its subsequent inheritance’ in the Entomologist’s Monthly Magazine,’ in 1926, replying to a paper published by the Royal Society by Dr Harrison and Dr Garrett, in which they described four years of experiments to demonstrate that melanism was induced by larvae feeding on plants contaminated by metallic salts. He asked why, if the test species Selenia bilunaria (Early Thorn) was so susceptible, did it not exhibit melanism in the areas where there was pollution ?

‘The authors of the paper assume – nay, assert (p.242) – that where Melanism occurs the atmosphere is polluted more or less largely by smoke; whereas surely every lepidopterist in Great Britain who has seriously studied the geographical range of melanism knows that such is not the case.’     He related the examples of ‘contradictory anomaly’ described above and concluded that although Harrison and Garrett’s theory was ‘a considerable advance’ on the smoke-blackened tree and bird predation theory of melanism,   ‘I cannot feel that as yet we really know much more about its cause in Nature than we did fifty years ago.’(38)[38]

When he died in January 1927 there was great concern that his unique collection would leave the district.  Its great scientific value, lay, not least, in‘…the large number of melanic specimens it contains’, emphasised Dr Thomas William Woodhead, (1863-1940) director of Tolson Museum, in the prospectus published to raise subscriptions. The £1,000 was donated, securing for the museum ‘a permanent record of one of Huddersfield’s foremost naturalists.’ (39)[39]

The collection was certainly of use to local naturalists.  The following year the Huddersfield Naturalist Photographic and Antiquarian Society announced that Ben Morley was to speak at Ravensknowle on ‘Mr Porritt’s work on Melanism Amongst Lepidoptera.’ (40)[40] It was probably Morley in his brief term as curator, who put together a large exhibition case illustrating variation, and particularly melanism in different species, which is unfortunately no longer on public view.  Exhibiting his own collection at Skelmanthorpe in 1927 he commented in his press interview on the increase in melanism among several species during his collecting lifetime. (41)[41]

Seth Mosley’s claim that Huddersfield was ‘the place of all places’ to seek an explanation for melanism may be overstated, but the work of Porritt and his contemporaries still has a valuable contribution to make to our understanding of the phenomenon.


Thanks to Chris Yeates, Museums Collections Officer, Kirklees Museums and Galleries for personally guiding me around the Porritt collection and photographing specimens, as well as  providing access to the Tolson Memorial Museum library and archives.  I am also indebted to Geoffrey Fryer for drawing my attention to his account in the YNU Bulletin of the breeding of A grossulariata by Huddersfield lepidopterists and for critical comments on this article.  Also to Prof Lawrence M Cook for some useful insights into the melanism debate which I have included in an appendix below. .

In referring to species I have used both the old and the current nomenclature, since the former was employed by local naturalists throughout the period we are describing.



[1]         1.Mosley, S.L. (1922)  ‘Nature Around Huddersfield’ Huddersfield Examiner (Weekly) HEW)  4 Feb 1922.

[2]         2. (Huddersfield Examiner  26 Nov 1870).

[3]         3. YNU (1896)       Naturalist 1896:21:227, ‘Bibliography of Lepidoptera 1892’, GTP, ‘Melanic Variety of Polia chi captured 1890 and 1891 at Huddersfield.’.

[4]         4. Tutt, J W (1891) ‘The British Noctuae and their Varieties’ Vols 1 and 2. (Sonnenschein, London)

Tutt, J W (!892) ‘The British Noctuae and their Varieties’ Vols 3 and 4. (Sonnenschein, London)

[5]         5.Tutt, J W (1891b) ‘Melanism & Melanochroism in British Lepidoptera’ (Sonnenschein, London) (p15. p.13)

[6]         6. Tutt, J W  (1896) ‘British Moths’ Routledge. London (Reprinted 1902)p  (305-307)

[7]         7. Porritt, G.T. (1906) Subsequently published almost verbatim in the HEW 1906 20 and 27 October  and in a summary in the Naturalist 1906.31:302-303.

[8]         8, (Porritt 1906)

[9]         9. Morley, B (1906) ‘Notes on Lepidopterous Variation in the Skelmanthorpe District’,  Naturalist 1906 .31: 49.

[10]        10. (Porritt 1906).

[11]        11. Morley, B. (1901) ‘Notes on the Lepidoptera of Skelmanthorpe During 1901’ Naturalist, 1902:27:141-144; . Morley, B (1906) YNU (1905)‘Yorkshire Lepidoptera in 1905’, YNU Ann. Rep. Entomological Section Naturalist 1906.31:.40).

[12]        12. Morley, B. (1914) ‘A Larva Plague in Deffer Wood, Yorkshire’.  Naturalist  39:151-152.  .

[13]        13. (Mosley 1917) Mosley, C. (1917) Huddersfield Naturalist and Photographic Society Annual Reports 1916-1917’.

[14]        14. Mosley, C (1918) Huddersfield Naturalist, Photographic and Antiquarian Society, Annual Reports 1917-1918’.

[15]        15. (Wattam 1919,1920).

[16]        16. (Butterfield   1919,1920)

[17]        17. YNU (1925) ‘YNU. Annual Report, 1925,’ Naturalist 1926.51:.56.

[18]        18. (Morley 1905,1906).

[19]        19. (Morley  1906’; South 1961 Series 1: 149)..

[20]        20. Morley, B (1909) ‘Notes on the Lepidoptera of South Yorkshire in 1908’.  Naturalist 1909. 34:18.

[21]        21. (Porritt 1920).

[22]        22. YNU 1925; Porritt, G.T. (1927) ‘The YNU’s 65th Annual Report for 1926’, Naturalist 1927.52:115-116.

[23]        23. (Morley 1906)

[24]        24. (Porritt 1926).

[25]        25. (Morley 1906).

[26]        26.Woodhead, T. W. (1927).  ‘The Porritt Collection of Insects’.

[27]      27.(South 1961,Series II:162)

[28]        28. Mosley, S.L. (1923) ‘Nature Around Huddersfield’ HEW 6 Jan 1923

[29]        29. Mosley, C (1904) Huddersfield Naturalist and Photographic Society, Annual Report 1904’.

[30]        30.(South 1961,Series 2, p.251)

[31]        31. Porritt, G T (1907) ‘Hereditary [sic] and Sexual Dimorphism in Abraxas grossulariata var. varleyata’ Entomologists Monthly Magazine Jan.

[32]        32, (Tutt 1896)

[33]        33. Fryer, G. (1998). ‘Stalwarts of the Past: Alfred Kaye 1867-1955’ and ‘Note on George Taylor Porritt and the recessive nature of Abraxas grossulariata ab. varleyata.’  Bulletin of the Yorkshire Naturalists’ Union 1998: 29:1-5.

[34]        34. (YNU 1910; Mosley, C 1917).

[35]        35.(Mosley, C 1920; Morley, B. (1920) Entomology Report’ ‘YNU: Annual Report, Entomological Section’ Naturalist 46:41.

[36]        36. (Porritt 1906)

[37]        37.Porritt,G.T. (1919) ‘Causes of Melanism in Phigalia pilosaria’ Correspondence, Naturalist, 1919.44:.340, 375.

Butterfield, E. P. (1920).  ‘Cause of Melanism in Phigalia pilosaria’ Correspondence, Naturalist, 45:78-79.

[38]        38. Porritt, G.T. (1926) ‘The induction of melanism in the lepidoptera and its subsequent inheritance’. Reprinted from ‘The Entomologist’s Monthly Magazine,’ Vol.  lxii . 1926. pp.107-111.  It was  also circulated as an off print. (A copy marked ‘With the Author’s Compt.’ is preserved in Huddersfield Local Studies Library).

[39]        39. Woodhead, T. W. (1927).  ‘The Porritt Collection of Insects’.; Huddersfield Examiner 30 Apr 1927)

[40] .      40. Huddersfield Examiner  6 Oct 1928

[41]        41. Huddersfield Examiner  19 Mar 1927


Professor Laurence Cook’s comments on the above article and some notes by me in response.

‘This is an account of the writings of SL Mosely and others, but especially of GT Porritt, on the evidence of increasing numbers of melanic forms in moth species in 19th century Yorkshire. The increases took place at a time when there were environmental changes due to urbanization and industrialization, and the writers wanted not only to record changes but also to understand why they should come about. A range of evidence and ideas is discussed. As such, it is an interesting account of a period in the history of natural history and an appropriate contribution for the Naturalist.

At the same time the author appears to suggest that the observations recorded have been neglected (the title) and overlooked, and that if that were not the case interpretations of the rise and decline of melanism would have been different. Here are some contrary sources which indicate that is not the case.

Early interest

1) In a series of contributions to the Entomologist’s Record, entitled Melanism and melanochroism in British Lepidoptera, JW Tutt (1891) goes through in detail the issues of why melanism arose. He also produced a book with the same year and title, published by Swan Sonnenschein, London.

Reply:  Porritt acknowledges Tutt’s work in his 1906 paper.  However, Porritt, (and most later commentators) regards Tutt as the leading early advocate of industrial melanism.  Porritt urges the consideration of other factors and it is on this aspect of his ideas that my paper is focused.  

2) In the early days there was a parallel group of Lancashire naturalists who discussed changes in melanic frequency and their causes in articles in the entomological journals. Incidentally, the first known carbonaria individual in the peppered moth dates from before 1811, but has no provenance, so we still do not know where the first sighting came from. Barrett (1901, The Lepidoptera of the British Isles. Vol. VII) and Doncaster (1906, Entomologists’ Record) summarize quite a lot of what was known at the time from all over the country. This was at the suggestion of William Bateson (1900, Entomologists’ Record), who wanted to get the information together and had already compiled a book called Materials for the study of variation (1894).

 Reply: I include Porritt’s contention that melanic types existed perhaps long before they were first noticed.  My concerns about industrial melanism are:

  1. the fact that it seems to develop objectively in nature, parallel to the development of the subjective interest in moth varieties and the increasing number of individuals and societies – particularly concentrated in the West Riding and Lancs – making observations and collections.
  2. the glib references to ‘industrialisation’. The problem is, when did industrialisation begin to have the environmental impact able to make an effect on moth populations ? And if this impact was mediated through the loss of lichen cover, when did it have a significant impact on those species ?  Industrialisation and urbanisation developed at a different pace in different areas even within the W Riding and Lancs.  Depending on the location of industrial premises, the emissions of smoke, the height of chimneys, prevailing wind and rain one area of woodland could be affected significantly whilst another nearby may not.  As Geoffrey Fryer and Jill Lucas point out ‘Soot and smoke do not disperse as readily as gases and their effects are more localised.’  (‘A Century and a half of Change in the Butterfly Fauna of the Huddersfield Area in Yorkshire’   The Naturalist 126: 2001.
  3. If crypsis gives a species selective advantage then it would seem that those exhibiting the most variety would obviously be the fittest. Are there pre industrial environmental factors which would favour melanism ? For example in early successional woodland birch may dominate.  Maturing birch trees darken and may give way to oak or beech with darker trunks.  Could this not significantly affect insect populations ?  Industrial factors would then be acting on an already established evolutionary mechanism.

1) Sutton, SL & Beaumont, HE. (1989, Butterflies and moths of Yorkshire. Yorkshire Naturalists’ Union, Doncaster) refers to melanics in most of the species mention by the early authors, and has a section on melanism where some of their issues are discussed.

3) A. pilosaria (by DR Lees), A. oxyacanthae & D. fagella (by RC Steward) and O. bidentata (by several people) have all been worked on extensively in the last three decades. Other species for which there is relatively recent work on genetics and distribution of colour variants are A. monoglypha, O. incerta and O. gothica. All of these produce results that differ somewhat from the peppered moth story and sometimes suggest other processes at work.

Later writings

HBD Kettlewell (1973, The evolution of melanism. Clarendon, Oxford) writes extensively about the early observations and about non-industrial melanism in moths, and cases that are difficult to ascribe one way or the other, including reference to Porritt (1906). At the end of the book he lists “259 British species having 449 melanic forms of which 175 are probably industrial”.

Reply:  How does Kettlewell arrive at  175 melanic forms as ‘probably industrial’ ?  Since it was not based on experimentation in every case then surely he is, to some degree, extrapolating from one species to another ?

2) Majerus (2002) discusses these issues thoroughly, including mention of Porritt’s 1906 paper.  In fact, he has two chapters on Lepidoptera other than betularia. His conclusion that melanism in that species is mainly due to differential predation may or may not be correct. However, he certainly does not overlook other species when reaching this conclusion and does not extrapolate from betularia to other species. Much of his work has been on melanic but aposematic beetles where this explanation would not apply.

Indeed, I quote Majerus in support of Porriit in warning against attributing a single cause or extrapolating from one species to another.

Cook et al. (2005) does not assume that Porritt was discussing melanism only in response to industrial pollution. The paper refers to cases where he noted changes during the period of industrialization and includes data on a species, A. crenata, in which the polymorphism is widespread throughout the country including non-industrial regions.

[The article (Cook, L. M., Sutton, S. L. and Crawford, T. J. ‘Melanic Moth Frequencies in Yorkshire, an Old English Industrial Hot Spot’ (Journal of Heredity 2005 96(5):522-528). states in its first paragraph:

‘It is well known that melanic forms in numerous moth species increased in frequency in parts of Britain following industrialisation in the 18th and 19th centuries…Blackening oif trees, buildings and vegetation was extreme, and the atmosphere was heavily polluted with a variety of toxic gases.  The response of moth populations in west Yorkshire was noteworthy enough for special comment when the British Association…met at York in 1906 (Porritt 1907)…Porritt lists 30 species in which such distinct black forms were regularly obtained. Of these seven had been obtained before industrialisation, whereas others were novel.  He added another 21 species in which dark individuals occurred so frequently as to suggest they were part of the same phenomenon…

This to me implies that it is the phenomenon of industrial melanism which is under discussion and that Porriit is describing melanism primarily in this context.  However, he is categorical in his 1906 paper that he is NOT attributing melanism to these conditions,

 ‘in the large manufacturing districts which have a humid atmosphere or heavy rainfall and hence it has been assumed that smoke and moisture aided by natural selection have produced the phenomenon.  Mt Tutt has argued the case from this standpoint at great length in his pamphlet ‘Melanism and Melanochroism in British Lepidoptera.’ No doubt it is true that melanism is almost confined to the western side of Britain, that is, the side most influenced by the Gulf Stream and also that it is most prevalent in the manufacturing, and consequently smoky districts of our island.  But if smoke is an essential how are we to account for the numerous and marked examples of melanism in the Hebrides, the Shetlands and Orkneys, where there is no smoke…’

I think here Porritt is quite clearly saying he does not subscribe to Tutt’s theory as a general explanation of melanism and that the ‘smoke theory’ was central to Tutt’s view.

Prof Cook’s conclusion:  ‘ So I think the account of the writings of the Yorkshire naturalists is interesting but that  the conclusion that their work is neglected and needs to be reconsidered to modify modern interpretation needs revising.’