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Letter 6051

Walsh, B. D. to Darwin, C. R.

25 Mar 1868

    Summary Add

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    Sexual preference in insects;

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    structures for seizing females;

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    Doubts whether CD can make much of a case from insects in support of sexual selection.


The Practical Entomologist, | Editor's Office, | Rock Island, Ill.,

March 25 1868

Chas— Darwin Esq.

Dear Sir,

I should have answered your letters of Feb. 14 & 17 sooner, but for bad health & being busy seeing my ``Report'' through the Press. I expect my copies of it tomorrow or next day, when I shall do myself the pleasure of sending you one.

After rummaging through my Journals & my entire Collection of Insects, I find but very little indeed that will answer your purpose. Such as it is, however, I enclose it. I always distrust my memory in such matters.

I do not believe that with Insects there is anything deserving the name of ``attachment'' or ``love''. The ♂ seeks the ♀ for copulation, & so soon as that process is accomplished, the partnership is dissolved. Even with some of the social Hymenoptera, (the Honey-bees) the ♂♂ are killed off as soon as their services can be dispensed with; & with the rest of them they die off. The only exception that I have heard of—& I must say that I am rather skeptical about it—is in the genus Tomicus (Scolytidæ in Coleoptera), where European authors say that the sexes unite in boring galleries under the bark, which are afterwards stocked with eggs by the females. I do not doubt the fact of the males boring these galleries, but I believe that they do it simply for food. Our Apple-twig Borer (Bostrichus bicaudatus, Say)


bores the pith of apple-twigs exclusively for food, no eggs being laid therein by ♀; & ♂♀ occur promiscuously, a single individual in a single boring, which is always commenced just above a bud.

I doubt if there be any use for ``the strange horns in ♂ Lamellicorns'', any more than for the tuft on the breast of ♂ Turkey, which you have referred to. In the Æschna family, there are earlets (``oreillettes'') one on each side of the basal abdomenal ♂ joint


(especially in the genus Gomphus,) which seem to be equally destitute of use. At least I can conceive no possible use for them. Gomphus is characterized by the eyes being almost as wide apart as in Agrion, & by the coloration being always black & yellow. G. vulgatissimus is an English species. In this group the tip of abdomen is clavate. The sexual distinctions in this genus are by no means conspicuous. I have enumerated such as occur in the species which have been described by me. The ♂♂ are by no means more brilliantly colored than ♀ ♀.

Westwood (Introd. II, p. 206) notices the fact of the male Ammophila (Sphegidæ, Hymenoptera) ``being exceedingly ardent during their amours, seizing their partners round the neck with their sickle-shaped jaws''. I have noticed the same thing myself a hundred times. He also notices (p. 205) that the jaws ♀ are used in burrowing. This is a case of the jaws being used for two distinct purposes; & in this genus jaws ♂♀ are alike or very nearly so.

I must confess I was surprised, on looking through my collection, to find so few conspicuous colorational distinctions in the sexes. Of course there are plenty of such distinctions which are of an inconspicuous character; but these you did not want.

On the whole, I doubt whether you can make out much in support of ``Sexual Selection'' from what we see with our eyes of Insects. I have little doubt that the principle is found or rather exists there; but it will perhaps always be hidden from us by the wide difference in our organs of perception. We may reason by analogy from the eye of a bird or even of a fish to that of a man; but we can scarcely do so from what is conventionally called the eye of an Insect to our own eyes.

Yours ever very truly, | Benj. D. Walsh

P.S. The questions about ``Expression'' are altogether out of my line. We have no Red Indians here.

When not otherwise specified in the enclosed paper, the sexes are equal in numbers, so far as I know.

[Enclosure: 1]

Order Neuroptera—Agrionidæ.

1. Calopteryx maculata has black wings ♂ ♀, ♂ deep opaque black, ♀ semitransparent smoky black. The ♀ (but not ♂) has a very conspicuous white ``pterostigma'' (as it is called) at the tip of each wing


2. In the very extensive N.A. genus Hetærina, ♂ (not ♀) has a beautiful carmine-red (or in some species brown) spot at the base of the wing. I enclose a ♂ specimen of H. tricolor Burm. (=rupamnensis Walsh), that you may see it for yourself. The males much the more numerous.


1. In Æschna clepsydra Say & A. constricta Say (two very closely allied species) the ground-color of ♂ abdomen is sky-blue, that of ♀ abdomen is pale grass-green. The difference is obvious, when they are on the wing.

2. In Anax junius ♂ the ground color of the basal parts of the abdomen is a most vivid ultramarine blue, in ♀ grass-green; in ♂ ♀ towards the tip of abdomen the ground-color becomes a dull pale lilac or purple. When on the wing, the coloring ♂ is very conspicuous.


1. In Plathemis 3-maculata Degeer the dark spots on the wings ♂ ♀ (both front & hind wings) differ, as per margin, the rest of wing being hyaline. There is never any the least hyaline spot at the tip of ♀ wing.



2. Both in the above species, in Libellula luctuosa Burm., in Mesothemis simplicicollis Say, & in Mes. longipennis Burm. the body of the mature ♂ becomes overspread with an external secretion of a milky-blue color on different parts of it, so as to be very conspicuous, especially in Pl. 3-maculata. Technically, this is known as ``pruinescence!'' & occurs also in some Agrion ♂ when mature. The immature ♂ differs in coloration in no respect from ♀ in all these insects.


About the enormous preponderance of ♀ ♀ in certain European Psocas, see Hagen in Proc. Ent. Soc. Phil., Oct. 1863, p. 168. (My Paper.)


In reference to the prehensile jaws of the Lucanidæ, which by the way I do not doubt may be used for pugnacious as well as amatory purposes, I have the following remarks in No. 10 Vol. II of the Practical Entomologist, p. 107



``We find another such case in a gigantic Fly with 4 gray wings, common near large rivers, (Corydalis cornutus, Linn.), where the jaws of the male are lengthened into the shape of the finger of a grain-cradle, evidently to enable him to embrace the soft body of the female; for, as jaws to bite or gnaw with, they are absolutely useless. In this instance, although the jaws, both of the perfect female fly & of the larva are armed with strong horny teeth, yet the jaws of the perfect male fly are quite smooth. The reason is evident. If they were armed with sharp prongs & teeth, they would penetrate the soft body of the female fly, & thus defeat the purpose for which nature constructed them. The Horn-bugs, on the contrary, are, as is well known, enveloped in a strong coat of mail; & here we find the prehensile jaws of the male armed with sharp prongs & teeth, & curved in such a manner as to give the best possible grip on the slippery shelly body of the female''.


The only conspicuous colorational distinction that I notice in this Order is Spectrum (diapheromera) femoratum Say; where ♂ is of a polished, shining brownish-yellow color, & ♀ of a dull, opaque, cinerous-brown color, when mature, but when immature ♂ ♀ are green.


Orsodacna atra Ahrens is black, legs & all; O. ruficollis Newman differs in having a rufous thorax. The former is the ♂, the latter the ♀, of one & the same species, & I have found them repeatedly in coitu.


In Anomoia laticlavis Forster, the ♂ has the anterior legs greatly elongated, & the tips of the front tibiæ crooked inwards, doubtless for sexual purposes.


Almost Universally, so far as I know, in the gall-making, species of Cynips the ♀ ♀ are at least 4 or 5 times as numerous as ♂ ♂; & in certain species there appear to be no ♂ ♂ at all, at least in ordinary seasons. So in the allied genus Rhodites, making galls on the Rose. In certain species the ♂ ♂ are very rare indeed. On the other hand, in the inquilinous Gall-flies, the sexes are about equal.


Curtis says ``It generally happens that the female saw-flies are much less abundant than the other sex, & this is believed to be the case with the Turnip-sawfly (Athalia spinarum), the males being as 6 to 1 when they have been bred; but it has been exactly the reverse in those I have caught in the fields, for out of 15 specimens there were only 3 males''. (Farm Insects, pp. 45--6) Probably it was a little late in the season; for it is a very general rule with Insects that ♂ comes out 2 or 3 days, or even 2 or 3 weeks, before ♀. Edwards finds this to be so with almost all Butterflies; & I have noticed it in many of the orders. For example, June 7 & 8 I bred 86 ♂ of a gall-making Gallfly, Cynips q. operator O.S., without a single ♀ among them; June 9 85 ♂, & only 4 ♀; June 10, out of 54 counted promiscuously, 52 were ♀. Sometimes (& I think generally with us) in the Sawflies the ♀ ♀ are the most numerous. Of Pristiphora grossulariæ Walsh (the N.A. gooseberry sawfly) I bred 4 ♂, 49 ♀; & of Cræsus latitarsus Norton I bred about 4 times as many ♀ as ♂


In Tremex columba Linn. the ♀ is much brighter-colored than ♂, having abdomen very variably banded with yellow, while ♂ has brown or piceous abdomen.—


In the gall-making Cecidomyia the ♀ ♀ are about 4 times as numerous as ♂ ♂. The discrepancy is especially remarkable in my Cec. s. batatas, of which I bred hundreds of ♀ to 1 ♂. In the inquilinous Cecidomyia, there seems to be little difference in numbers.

Lepidoptera—the Butterflies.

Throughout Papilio, the ♂ ♂ are 4 times (about) as numerous as ♀ ♀. In many species the ♀ is hard to get. This is what Edwards says; & he has large experience, receiving many collections from all quarters, & collecting himself extensively. In Papilio Turnus the ♂ ♂ are certainly at least 4 times as numerous as ♀ ♀; we have only 4 species of the genus here.

In Pieris protodice the ♂ ♂ are remarkably less marked with black than ♀ ♀; so that, when I began collecting, I took them for distinct species. So far as I recollect, the same law prevails with your English species. In Parnassius smintheus (the only species of the genus I have) the same thing holds good. Almost any one at first sight would take the ♀ for a different species.— In Hipparchia nephele (color brown) the ♂ is always several shades darker than ♀, so that I at first thought them distinct species.— In Nathalis iole, ♀ has a good deal more black than ♂ on upper face of hind wing, & in ♂, there is a singular oval white spot (B)


enclosed in the black band on the upper face of the hind wing, so as to be generally concealed by the overlap of the front wing, which is not found in ♀. On the other hand, in Colias philodice, C. eurytheme, & C. cæsonia, ♂ has more black in both wings above than ♀; & I believe it is the same in your European species, Edusa & hyale.— In Danais archippus ♂ has a singular black spot (A) by the side of one of the veins of the hind wing, which is not found in ♀.


In Thecla falacer? Bdv. & Lec. the ♂ has an oval spot of a paler brown color & shining, on the middle of the subcosta above, which is absent in ♀.— In Thecla poeas? Hübn., one sex (I think ♀) is mostly bright blue above, the other brown.— In Polyommatus neglectus & P. pseudargiolus, ♂ wings are blue immaculate above, ♀ broadly edged with black except behind. In P. comyntas Godt., P. lygdamas Doubl., P. heteronea Bdv., & P. acmon Doubl., ♂ wings are blue above, ♀ brown (more or less tinged with blue) or reddish brown.— Argynnis Diana, you know all about the coloration; as to the numbers of the sexes, I think that Edwards found them about equal. At all events, he told me nothing to the contrary.

Lepidoptera--the Moths.

In Cossus robiniæ the top half of the hind wing is orange not uniform dull gray as in ♀.— In Ægeria exitiosa Say. ♀ there is a broad orange band on middle of the steel-blue abdomen not found in ♂; but ♂ front wing is mostly hyaline & that of ♀ steel-blue opaque.— In Saturnia io ground-color of ♂ wings is bright ochre-yellow, instead of reddish brown as in ♀.— In Acontia (2 species) a genus of Tineidæ, ♀ has a good deal more black than ♂.

    Footnotes Add

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    f1 6051.f1
    Letters to B. D. Walsh, 14 February 1868 and 17 February [1868].
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    f2 6051.f2
    Walsh refers to his First annual report on the noxious insects of Illinois (B. D. Walsh 1868). CD's lightly annotated copy is in the Darwin Pamphlet Collection, CUL.
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    f3 6051.f3
    Walsh refers to the bark beetles (genus Tomicus, subfamily Scolytinae). For more on mating systems in Tomicus, see Kirkendall 1983, pp. 302, 306.
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    f4 6051.f4
    Bostrichus bicaudatus, the apple-twig borer, is now Amphicerus bicaudatus (family Bostrichidae).
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    f5 6051.f5
    In Variation 1: 293, CD mentioned the presence of a tuft of hair on the breast of male turkeys.
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    f6 6051.f6
    The genus name Aeschna is a synonym of Aeshna (family Aeshnidae, darners) while Gomphus is a genus in the family Gomphidae, clubtails; both belong to the suborder Anisoptera, dragonflies. The earlets that Walsh refers to are now known as auricles, found on either side of the second abdominal segment in males of some families of Anisoptera. It is now thought that the purpose of the auricles is to guide the female's abdomen into the optimal position for copulation (Silsby 2001, p. 12).
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    f7 6051.f7
    Agrion is now Calopteryx, a genus of demoiselle damselfly (see Montgomery 1954). Gomphus vulgatissimus, the club-tailed dragonfly, occurs locally in southern England and Wales (see S. Brooks ed. 1997, p. 118). In Descent 1: 362, CD cited Walsh for information on colour differences between the sexes in dragonflies.
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    f8 6051.f8
    The quotation is from John Obadiah Westwood's Introduction to the modern classification of insects (Westwood 1839--40, 2: 206). The passage is scored in CD's copy; similarly CD underlined the passage about jaws being used for burrowing (Westwood 1839--40, 2: 205). Ammophila is a genus of sand wasp of the family Sphegidae (now Sphecidae). In Descent 1: 342 and n. 5, CD quoted the passage from Westwood and cited Walsh for calling it to his attention.
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    f9 6051.f9
    Walsh is probably alluding to the compound insect eye, which is composed of anything from a few to several thousand facets.
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    f10 6051.f10
    CD had evidently enclosed a copy of his queries about expression in his letter to Walsh of 14 February 1868 (see Correspondence vol. 16, Appendix V).
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    f11 6051.f11
    Agrionidae is a synonym of Calopterygidae, the family of broad-winged damselflies. The family now belongs to the order Odonata (dragonflies and damselflies), suborder Zygoptera. The order Neuroptera is now restricted to lacewings and their kin.
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    f12 6051.f12
    Calopteryx maculata is the ebony jewelwing damselfly.
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    f13 6051.f13
    Hetaerina is the genus of rubyspot damselflies. Hetaerina tricolor and H. rupamnensis (as described in B. D. Walsh 1863a, pp. 230--3) are synonyms of H. titia, the smoky rubyspot damselfly (see Garrison 1990, p. 227). In Descent 1: 362, CD mentioned the carmine spot in Hetaerina males.
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    f14 6051.f14
    Aeschnidae is a synonym of the family name Aeshnidae (see n. 6, above).
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    f15 6051.f15
    Aeschna clepsydra, the mottled darner, is now Aeshna clepsydra.Aeshna constricta is the lance-tipped darner.
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    f16 6051.f16
    Anax junius is the green darner.
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    f17 6051.f17
    The dragonfly family Libellulidae (common skimmers), is now in the order Odonata, suborder Anisoptera.
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    f18 6051.f18
    Plathemis trimaculata is now Libellula lydia, the common whitetail dragonfly.
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    f19 6051.f19
    Libellula luctuosa is the widow skimmer dragonfly; Mesothemis simplicicollis, the eastern pondhawk dragonfly (now Erythemis simplicicollis); M. longipennis, the blue dasher dragonfly (now Pachydiplax longipennis). On Agrion, see n. 7, above. In Descent 1: 363, CD mentions the differences in appearance caused by pruinescence but does not use the technical term, which is first recorded in print in 1890 (OED).
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    f20 6051.f20
    The family Psocidae is now in the order Psocoptera, bark lice.
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    f21 6051.f21
    Walsh refers to the paper, `Observations on certain N.A. Neuroptera, by H. Hagen' (B. D. Walsh 1863a). The paper consists of Walsh's translation of observations by Hermann August Hagen, along with some new species descriptions by Walsh himself. CD scored the passage on the preponderance of females in his copy of the article (Darwin Pamphlet Collection--CUL).
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    f22 6051.f22
    The family Sialidae (alderflies) is now in the order Megaloptera (alderflies, dobsonflies, fishflies).
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    f23 6051.f23
    The passage quoted is from the `Answers to correspondents' section of Practical Entomologist 2 (1867): 107; Walsh, the magazine's editor, wrote all the replies.
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    f24 6051.f24
    Corydalis cornutus is the dobsonfly.
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    f25 6051.f25
    The family Phasmidae (now Phasmatidae, walking sticks) is now in the order Phasmida. The order Orthoptera is now restricted to crickets, grasshoppers, katydids, and locusts.
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    f26 6051.f26
    Spectrum femoratum, the walking stick, is now Diapheromera femorata, the northern walking stick. In Descent 1: 361, CD quoted Walsh's description of the colour differences in the sexes of S. femoratum.
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    f27 6051.f27
    The family Crioceridae is now the subfamily Criocerinae of the family Chrysomelidae, leaf beetles, in the order Coleoptera.
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    f28 6051.f28
    Orsodacna atra and O. ruficollis are now both Orsodacne atra (subfamily Orsodacninae, family Chrysomelidae). In Descent 1: 368 n. 58, CD cited Walsh on colour differences in the sexes of O. atra.
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    f29 6051.f29
    The family Cryptocephalidae is now the subfamily Cryptocephalinae in the family Chrysomelidae, leaf beetles, in the order Coleoptera.
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    f30 6051.f30
    Walsh evidently refers to Anomoea laticlavia, the clay-coloured leaf beetle. It is now placed in the subfamily Clytrinae, family Chrysomelidae.
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    f31 6051.f31
    Cynipidae is the family of gall wasps.
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    f32 6051.f32
    Rhodites is now Diplolepis. In Descent 1: 314, CD cited Walsh on the proportion of sexes in Cynipidae.
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    f33 6051.f33
    Tenthredinidae is the family of saw-flies.
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    f34 6051.f34
    The reference is to John Curtis and Curtis 1860. In Descent 1: 314, CD cited the information from Curtis. Athalia spinarum, the turnip saw-fly, is now A. rosae.
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    f35 6051.f35
    William Henry Edwards.
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    f36 6051.f36
    Cynips quercus operator is now Callirhytis operator, the pip gall wasp.
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    f37 6051.f37
    Pristiphora grossulariae (described as a new species by Walsh in Practical Entomologist 1 (1866): 123--4) is now considered to be a synonym of Pristiphora rufipes. Craesus latitarsus is now Croesus latitarsus, the dusky birch saw-fly.
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    f38 6051.f38
    The family Uroceridae, horntail wasps, is now Siricidae.
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    f39 6051.f39
    Tremex columba is the pigeon tremex. In Descent 1: 365, CD refers to the species as T. columbae (family Siricidae) and cites Walsh on colour differences in the sexes.
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    f40 6051.f40
    The family Cecidomyidae is now Cecidomyiidae, gall midges.
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    f41 6051.f41
    Walsh refers to Cecidomyia salicisbatatas, the willow potatogall midge, now Rabdophaga salicisbatatas. In Descent 1: 314, CD cites Walsh on the proportion of sexes in gall-making Cecidomyiidae.
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    f42 6051.f42
    Papilio turnus, the tiger swallowtail, is now P. glaucus; in Descent 1: 309--10, CD cited Edwards on the proportion of the sexes in Papilio and mentioned Walsh's observations on the numbers in P. turnus.
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    f43 6051.f43
    Pieris protodice, the checkered white butterfly, is now Pontia protodice.
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    f44 6051.f44
    Parnassius smintheus is the Rocky Mountain parnassian.
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    f45 6051.f45
    Hipparchia nephele, the clouded wood nymph, is now a subspecies of Cercyonis pegala, the common wood nymph. In Descent 1: 387, CD noted that English meadow-browns (`Hipparchiæ'; on the use of `Hipparchia' as a general term for satyrid species, see Emmet 1991, p. 30) had similarly coloured sexes.
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    f46 6051.f46
    Nathalis iole is the dainty sulphur butterfly.
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    f47 6051.f47
    Colias philodice is the clouded sulphur; C. eurytheme, the orange sulphur; C. caesonia (now C. cesonia), the southern dogface; C. edusa (now C. croceus), the clouded yellow; and C. hyale, the pale clouded yellow.
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    f48 6051.f48
    Danais archippus, the monarch butterfly, is now Danaus plexippus.
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    f49 6051.f49
    Thecla falacer is now a subspecies of Satyrium calanus, the banded hairstreak. Thecla poeas is now Calycopis cecrops, the red-banded hairstreak.
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    f50 6051.f50
    The name Polyommatus neglectus was not at the time published (the recently published name, P. neglectus (Stradomsky and Arzanov 1999), refers to a different butterfly), but Walsh probably refers to the species Lycaena neglecta, now Celastrina neglecta, the summer azure. The unpublished name Polyommatus pseudargiolus was probably used by Walsh to refer to Argus pseudargiolus, now Celastrina ladon, the spring azure.
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    f51 6051.f51
    Polyommatus comyntas is now Everes comyntas, the eastern tailed-blue. The butterfly Walsh refers to as P. lygdamas was Lycaena lygdamus (see Doubleday and Westwood 1846--52, 2: 491), now Glaucopsyche lygdamus, the silver blue. Polyommatus heteronea (see Morris 1862, p. 89) is now Lycaena heteronea, the blue copper. The butterfly Walsh refers to as P. acmon was Lycaena acmon (see Doubleday and Westwood 1846--52, 2: 494), now Plebejus acmon, the acmon blue.
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    f52 6051.f52
    Argynnis diana, now Speyeria diana, the Diana fritillary, is highly sexually dimorphic. Edwards described the female of the species in W. H. Edwards 1864.
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    f53 6051.f53
    Cossus robiniae is now Prionoxystus robiniae, the carpenterworm moth.
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    f54 6051.f54
    Aegeria exitiosa is now Synanthedon exitiosa, the peachtree borer.
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    f55 6051.f55
    Saturnia io is now Automeris io, the io moth. In Descent 1: 398, CD mentioned the colour differences in Saturnia io, but did not cite Walsh for the information.
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    f56 6051.f56
    The genus Acontia in fact belonged to the family Acontidae (see Stainton 1856--9, 1: 295--7). It now belongs to the subfamily Acontiinae, family Noctuidae (noctuid, dagger, and owlet moths).
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