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
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 Esq
- f1 6046.f1Alfred 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  and n. 4).
- f2 6046.f2Vanessa 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.
- f3 6046.f3Porthesia auriflua is now Euproctis similis; the white ermine, Spilosoma menthastri, is now S. lubricipeda.
- f4 6046.f4Caterpillars of Spilosoma menthastri are black with long brown hairs and an orange stripe down the back.
- f5 6046.f5Females 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.
- f6 6046.f6The geodephaga are a tribe of terrestrial and predaceous beetles (OED); the family Blattae is now known as Blattidae.