Darwin Correspondence Project

King St. Leicester

31 Novem 1861

My Dear Sir

The following are the references which I promised.

Volucella bombylans

V. bombylans (red-tipped abdomen)

V. plumata (Meigen) (= mystacea Fab) (white-tipped abdomen)

M. Macquart (Hist. Nat. des Dipt`eres Vol. 1 1834, p 494) places both together, terming V. plumata ``vari´et´e constante'' of V. bombylans. at p 479 he quotes M. de St Fargeau who observed the accouplement of the two forms: and stated moreover that the two other European Volucellæ also had each a constant variety. A kind of Dimorphism?

Zeller (Entom. Zeitung, 1842 p 65) confirms the above statement from personal observation, as to V. bomb. & V. plumata.

Erichson (Entom. Zeitung 1842 p 113) described all the known varieties of the species. They were then 7—No 1 being the true bombylans which passed gradually into plumata through V. hæmorrhoidalis (Zetterstedt) and others.

On the meaning of the colours and markings of butterflies' wings. The article on the subject which I mentioned to you is by Dr. R¨ossler in the Wiener Entomologische Monatschrift 1861 p 163. On reading it through carefully I find many interesting facts, which I should have done well to quote in my paper but I wrote it before Dr. R's was published. He says plainly that the colours & markings are given to deceive the enemies of the species. All the facts are from European insects. He is wrong in saying that ``it is a general law that animals are clothed in the colours of their resting places.'' This is a kind of mistake which we are all apt to fall into.

I think the whole tenour of your book teaches what I carefully insisted on in my paper that the welfare of species is the object of all structures & forms. All species exist by virtue of some endowment enabling them to withstand adverse circumstances. If an exact mimetic dress be not required to enable a species to maintain itself, the causes which tend to produce it will not operate. There are species of the same genus of similar habits & living on the same soil; one of which is of the colour of the soil and another of a completely contrasted colour. Therefore it is not a general law that a parasitic species shall mimic its victim &c &c.   the mimicry is only part of the wider law above mentioned & the exceptions are proved as they ought to be by the same wider law.

Dr Rossler remarks that the underside of the Vanessa & other butterflies are coloured to resemble the bark of trees; because as they close the wings when they alight, they become suddenly invisible. In moths (Noctuæ) which rest with wings deflexed the upper covering the lower it is the upper surface of the upper wing only which imitates bark. I will mention that in some of these moths (Catocala) the underwings are of brilliant colours; So that here we have a double dress answering two purposes in the welfare of the species. The high colour being explicable by sexual selection & the plain colour by the check caused by insectivorous animals.

The essay of Burmeister's which I mentioned as probably worth reading is called Vergangenheit & Gegenwart des Thierreichs