594 



NA TURE 



\Oct. 20, 1887 



formate, all corresponded almost exactly to the weights which 

 would have been given by pure aqueous formic acid having this 

 composition : water, 62'5 per cent. ; formic acid, 37 "5 per cent. 

 Since writing the above I have received the results of Prof. 

 Meldola's analysis, from which he concludes that the secretion 

 consists of aqueous formic acid almost in a state of purity. 



Further Experiments upon the Colour- Relation betiueen Phyto- 

 phagous LarvcB and their surroundings, by E. B. Poulton. — 

 From the instance of the larval Smerinthits ocellatus, I have 

 shown that certain Lepidopterous larvae are susceptible to the 

 influence of surrounding colours, so that the larvse themselves 

 gain a corresponding appearance.-^ This larva varies from 

 bright yellowish-green to a dull whitish or bluish-green, and 

 either variety can be produced by the use of a food-plant, with 

 'the appropriate colour on the under side of the leaves. Although 

 the difference between the two varieties is very great when they 

 are placed together, so great in fact that 1 can readily 

 distinguish three intermediate stages of variation between the 

 extremes — yet it is not nearly so well marked as in the case of 

 the green and brown varieties of many dimorphic larvse. I was 

 therefore anxious to test one of these latter, and to ascertain 

 whether either variety can be produced at will by surrounding 

 the larva with the appropriate colour. Lord Walsingham had 

 previously called my attention to the variable larva; of Ruinia 

 cratagata, some of which are brown, some green, while many 

 are intermediate. The larva exactly resembles the twigs of its 

 food-plant, and always rests upon the branches in a twig-like 

 attitude, and this habit rendered the species very favourable for 

 the purpose of this inquiry, which was conducted as follows : — 

 A glass cylinder was provided with a black paper roof, and a 

 similar floor, and a small quantity of the food-plant — hawthorn 

 — the rest of the space being entirely filled with dark twigs. 

 Owing to their habit, the larvae always rested upon these latter, 

 and after reaching maturity in two such cylinders, forty dark 

 varieties were produced. Three other cylinders were roofed 

 and floored with green paper, and green shoots bearing leaves 

 were introduced as food, nothing brown being allowed inside 

 the cylinder. In these cylinders tweaty-eight green varieties 

 were produced. The young larvae were obtained from the eggs 

 of three captured females. After hatching, the larva; were tho- 

 roughly mixed and introduced into the cylinders when quite small. 

 Some of the dark varieties were greenish, and some of the green 

 larvse brownish, but the greenest in the dark cylinders was browner 

 thm the brownest in the green cylinders. The larvK were 

 compared by placing the sets side by side upon white paper, and 

 the contrast between the larvse brought up in different surroundings 

 was very marked. In this case the larvas ate precisely the 

 same kind of leaf, so that it is clear that the effects follow from 

 the surrounding colours, and not from the action of food. The in- 

 stance recorded above is the best among the many cases of adjust- 

 able colour-relation which are now known in Lepidopterous 

 3ai-vj;. It is now extremely probible that all dimorphic species 

 will show more or less of this susceptibility to the colours of their 

 environment. 



Further Experiments upon the Protective Value op Colour 

 and Markings in Insects, by E. B. Poulton. — The experiments 

 undertaken in 1886, of which a short account was given in a 

 paper read before Section D, at Birmingham, led to such interest- 

 ing results that I determined to renew the investigation during the 

 present year.'-^ At the same time the range of the inquiry has 

 'been widened, and for the first time a mammal has been included 

 in the list of insect-eating vertebrates used in the experiments. 

 For this purpose a marmoset has been employed, and this animal 

 appears to be highly insectivorous. With the kind help of 

 Mr. A. G. Butler I have been able to add largely to the number 

 of experiments made with birds, and these results have been 

 ■especially needed. In addition to the species of lizards and 

 'frogs made use of last year, I have also experiment'^d with a 

 ■chamseleon and a salamander. The c )mparison of the results 

 ■obtained from these different groups of insect-eaters is extremely 

 interesting. In nearly all cases there is complete c mcurrence in 

 their treatment of highly-coloured nauseous insects. But there 

 are great differences in the relative ease with which the different 

 groups can be induced by hunger to eat distasteful insect food. 



The frogs and the birds appear to be the least scrupulous in this 

 respect. It seems probable that the superficial skin of the frog 



An account of these experiments will be found in Proc. Roy. Soc, 

 No. 237, 1885, p. 269, and No. 243, 1886, p. 135. 



For the complete account of the experiments in i886 see a paper by 

 the author in Proc. Zool. Soc, Lond., March i, 1887, pp 191-1-74. 



is more delicate than the lining of the oral cavity. Thus the 

 Hymenopterous larva;, Cra'sus scptentrionalis a.n(\. C. varus, were 

 eaten in considerable numbers, but the face was carefully wiped 

 by the paw after being touched by the everted glands of the 

 larvEE. I am inclined to think that lizards are less unscrupulous 

 in this respect than the most completely insect -eating birds. 

 Mammalia [i.e. the marmoset), appear to be far more difficult to 

 please than any of the other groups. The above arrangement 

 accords well with what is known on other grounds of the 

 development of the sense of taste in the vertebrate classes. 



I will now bring forward a few of the instances which support the 

 above-mentioned conclusions. The marmoset would never touch 

 a hairy or spinous larva of any kind ; this was because of the 

 presence of the structures themselves, for the same species was 

 always eaten in the pupal stage. All the other vertebrates will 

 sometimes eat hairy larvse. Birds have a special advantage in 

 their power of getting rid of impleasant appendages — such as 

 hairs or wings. Large lizards will eat unpalatable insects which 

 are often refused by smaller ones, probably because the former 

 can swallow their p:ey without so much biting, and thus without 

 tasting it so much. Lady-birds were eaten by the nightingale, 

 and by frogs when very hungry ; hitherto they have been in- 

 variably refused by the other vertebrates. The green larva of 

 Pieris rapce was eaten, but disliked by the marmoset, relished 

 by the lizards. The hairy larva of Orgyia antiqua was eaten 

 by birds but refused by lizards, except on one occasion, when 

 two lizards fought over the larva, and in the struggle tore out the 

 hairs incidentally. An experiment with this latter larva gave a 

 very probable interpretation of the meaning of the hairy tufts on 

 many Bombyx larvse. A lizard seized the larva by one of these 

 tufts, which immediately came out, leaving the lizard with a 

 mouthful of hairs. After this it did not again touch the larva. 

 These tufts are placed on the back, in the part where larva; are 

 nearly always seized ; being formed of very closely approximated 

 fine hairs of the same height, the whole tuft suggests a solid part 

 of the animal rather than a mass of loosely fixed hairs. 



The following con-picuous nauseous forms have been eaten, 

 when the vertebrates have been hungry : — 



Euchelia jacobcrcE, larva, by lizard. 



Pygcera bucephala , larva, by lizard. 



Porthesia aurijlua, larva, by lizard. 



ZygcEua filipendida, imago, by lizard. 



Zyga'na tripolii, imago, by frog. 



Diloba ccBruleocephala, larva, by lizard. 



Liparis salicis, larva, by lizard. 



Liparis salicis, imago, by lizard and marmoset. 



Abraxas grossulariata, imago, by lizard. 1 



L. salicis (imago) is evidently very distasteful, but the very 

 similar (although smaller) P. aurijlua (imago) is palatable, and 

 the latter probably benefits by the reputation of the former. 

 Thus the marmoset when very hungry ate the former, although 

 it was much disliked ; immediately afterwards the mammal 

 refused the latter, although on other occasions he ate as many as 

 four of these moths with evident relish. Highly-gilded pupae of 

 Vanessa tirticcE were eaten with relish by birds and the 

 marmoset, and it is clear that the appearance does not in this 

 case indicate an unpleasant taste, as has been suggested. The 

 spider-like larva of Stauropus fagi, in its terrifying attitude, 

 somewhat impressed a lizard and the marmoset, but not to such 

 an extent as to prevent the larva from being eaten. This was to 

 be expected, for both animals will eagerly devour spiders. Such 

 effect as was produced was due to the suggestion of no ordinary 

 English spider, but one of much greater size, and with the 

 terrific aspect highly idealized. The terrifying larva of Cer^ 

 vinula certainly frightened the marmoset, and either its appg 

 ance or the secretion of formic acid greatly affected the lizatj 

 The terrifying but quite harmless larva of Chccrocampa elpen 

 which is known to frighten all but the boldest of birds (as Wd 

 mann has shown) was offered to a large lizard. The latj 

 examined the larva most cautiously and many times bcf! 

 touching it ; then it bit the larva gently, and retired to wa^ 

 the effect, repeating this process several times. Finally, finditi 

 that nothing happened, it seiz;d the larva, and soon swalloweg 

 it. The effect produced by this serpent-like larva was not ' 

 to its size, for the equally large larvse of Smerinthus ocellA 

 were seized at once. The imagines of Sesia bembeciformis 

 S. apiformis, resembling hornets, were offered to lizards, 

 the first occasion the moth was approached with the greaS 

 caution, examined carefully, and seized by the head and thoir 



