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Letter 6046

Weir, J. J. to Darwin, C. R.

24 Mar 1868

    Summary Add

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    Experiments to test Wallace's theory that brightly coloured caterpillars are rejected by birds. [See Descent 1: 417.]


6 Haddo Villas | Blackheath SE

24 Mch 1868

My Dear Sir

I hope you will clearly understand that it is by no means necessary to reply to my letters, but on the contrary I have endeavoured, knowing how valuable your time is, so to word them that no answer is needed.—

I have by no means arrived at many facts regarding Wallaces theory, accounting for the bright colors of caterpillars by supposing that birds are warned that such species are of bad flavor, still all last Summer I made continual experiments.—

Up to the present time the birds experimented on have refused all conspicuous larvæ & have eaten greedily ``all species of nocturnal or retiring habits & whose colors assimilated them to their food plants.—

Vanessa Io & V Urticæ both species whose caterpillars are most conspicuous on Nettles were decidedly refused, not even regarded although crawling for hours about the aviary.—

Their metallic pupæ were likewise allowed to remain day after day unheeded by the birds.—

The larvæ of the

Garden Tiger, Arctia Caja

Small Eggar, Eriogaster lanestris

Gold Tail, Porthesia auriflua,

Vapourer, Orgyia antiqua

Ermine, Spilosoma menthastri

were all refused by the birds although left in the Aviary for days.—

In order to ascertain whether these caterpillars were rejected on account of flavor I took a large number of young Menthastri (say 100) and placed in the Aviary, their character was then undeveloped & the larvæ were but 14 inch long, most of the birds paid no attention to them, although they were crawling about on a leaf, but two or three birds seeing them move came up to the leaf and tasted one or two, but at once turned away leaving the remainder unmolested.—

The actions of the birds shewed plainly, by shaking the head and cleaning the beak that an unsavoury morsel had been taken into the mouth.

The ♀ of Orgyia antiqua in the imago state never leaves the cocoon but as it deposits its eggs, it is often nearly an inch in length with the abdomen very much distended with ova, it is conspicuous on palings & seems a nice fat mouthful for an insectivorous bird, but by the birds in my aviary it was universally refused.—

It is to be noted that my birds were very tame & were constantly on the lookout for insects to be thrown to them, they would take without hesitation Woodlice, Centipedes, Millipedes Geodephagous Beetles, Cockroaches (Blattæ), Weevils (Curculionidæ & with avidity Spiders.—

The latter much surprizes me, but they like nothing better, but in nature the spiders seem protected, perhaps by their webs?—

Yours very truly | J Jenner Weir

C Darwin Esqr.

    Footnotes Add

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    f1 6046.f1
    Alfred Russel Wallace had asked Weir to carry out experiments to test Wallace's theory that brightly coloured caterpillars would be refused by birds (see Correspondence vol. 15, letter from A. R. Wallace, 24 February [1867] and n. 4).
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    f2 6046.f2
    Vanessa io, the peacock butterfly, is now Inachis io; V. urticae, the small tortoiseshell butterfly, is now Aglais urticae. These species have black and black and yellow caterpillars respectively.
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    f3 6046.f3
    Porthesia auriflua is now Euproctis similis; the white ermine, Spilosoma menthastri, is now S. lubricipeda.
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    f4 6046.f4
    Caterpillars of Spilosoma menthastri are black with long brown hairs and an orange stripe down the back.
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    f5 6046.f5
    Females of Orgyia antiqua have only rudimentary wings and relatively large bodies and therefore have very limited mobility. They deposit their eggs on the outside of the cocoon.
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    f6 6046.f6
    The geodephaga are a tribe of terrestrial and predaceous beetles (OED); the family Blattae is now known as Blattidae.
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