84 



KNOWLEDGE 



[February 1, 1893. 



great force from small glands distributed over the body. 

 These liquids are very volatile, and therefore, though the 

 jet itself may not reach the assailant, the atmosphei-e 

 around becomes charged with the vapour aud is thus 

 rendered repulsive, warning oft' the enemy. 



As caterpillars constitute the staple food of many verte- 

 brate animals, especially certain species of birds and 

 reptiles, it becomes an interesting enquiry whether, 

 amongst the great multitude of species, all are equally 

 palatable to each insectivorous vertebrate, and would 

 therefore be taken indifferently ; or whether, on the other 

 hand, any choice is exercised, and there are any kinds of 

 caterpillars for which a decided preference is manifested, or 

 whether any are absolutely repugnant to the taste, and if 

 so, how the distasteful ones are recognized so as to be 

 avoided. Observations and experiments made in connec- 

 tion with various kinds of birds and reptiles in confinement 

 have clearly demonstrated that all caterpillars are not 

 regarded by them as alike suitable for food, and there are 

 many indications that, when any are rejected or only 

 reluctantly taken, it is because of something unpleasant 

 in the taste that they are thus treated. The more refined 

 taste of modern civilized society is prejudiced against the 

 use of caterpillars as an article of diet ; nevertheless, it is 

 a well-known fact that some species are sufficiently palat- 

 able to have been used with relish as food by human 

 beings ; and though it would be unsafe to argue at once 

 from human partialities to those of the lower animals, 

 there is probably enough in common between the palate 

 of man and that of bird or reptile to permit of our forming 

 some notion as to what might be ((/(palatable to these lower 

 animals . For example , we know enough of the effects of acrid 

 or ftetid liquids to render it a safe assumption that cater- 

 pillars which secrete such fluids will for that reason prove 

 to be unpalatable to birds and reptiles ; and the same 

 might be expected to be the case with such as feed upon 

 plants possessing strong and disagreeable tastes or poisonous 

 properties. At the same time, just as to us a little 

 acidity is by no means a drawback in an article of diet, 

 but on the contrary imparts a stimulating and refreshing 

 flavour, so caterpillars that secrete acid juices might be 

 expected not to become thereby unpalatable unless the 

 secretion were excessive. This supposition is borne out 

 by the instance of the puss moth caterpillar above referred 

 to. Notwithstanding its secretion of formic acid, it is 

 eagerly devoured by lizards, and that too in defiance of its 

 somewhat alarming aspect and the whisking movement 

 of its whip-like tails, so that it must evidently be regarded 

 in the reptilian world as a savoury morsel whose acquisition 

 is worth some risk. 



At a meeting of the Entomological Society of London 

 in 18G7, Mr. A. R. Wallace, the apostle of natural selec- 

 tion, ventured to predict that caterpillars which were very 

 brightly coloured and conspicuous would be found to be 

 distasteful to some at least of their bird enemies, the 

 suggestion being that the caterpillars had acquired the 

 intensity of their colour by a process of natural selection, 

 their conspicuous appearance serving as a danger signal 

 or warning to their vertebrate foes that they were inedible ; 

 thus the warning became the more perfect and the pro- 

 tection afforded therefore the more complete in proportion 

 to the intensity of the coloration. Acting upon this hint, 

 several competent observers made repeated trials of the 

 behaviour of various birds and reptiles towards about a 

 hundred species of caterpillars. Mr. J. Jenner Weir, 

 experimenting with such birds as robins, yellow hammers, 

 chaffinches, thrushes, ('i:c., showed that green caterpillars 

 were always eaten with relish, as were also those that were 

 dull-coloured, with fleshy bodies and smooth skins ; brown 



Fig. 14. — Caterpillar of Magpio 

 Moth. 



or green geometric larvse also were invariably eaten. Very 

 conspicuous larvse, on the other hand, such as those of 

 the magpie moth (AhniAri.s iii-dsstdayidta) (Fig. 14), which 

 is distinctly marked with 

 black and orange on a 

 cream-coloured ground, 

 the figure-of-eight moth 

 (Diloha cmruh'ovejilu(la'), 

 which is greenish or 

 bluish white, with dis- 

 tinct black and yellow 

 spots and stripes, and 

 the mullein moth [CucuUia rerlmsci), which is also greenish 

 white with black and yellow markings, were not molested 

 by the birds. 



Miss Lilian Gould has recently made further experi- 

 ments with the two last-na,med insects, which seem to 

 indicate that these caterpillars are really disagreeable to 

 the avian taste. The bird employed as judge was a tame 

 jackdaw of about a twelvemonth old. As it had been 

 captured while still unfledged, it certainly could have had 

 no personal exi^erience of caterpillars in a state of nature ; 

 and during the twelvemonth of its captivity, its only 

 chance of gaining any knowledge of them and their 

 edibility would be the possible fall into its cage of casual 

 specimens dropping from the beech tree under which it 

 was kept, and this was evidently a rather remote contin- 

 gency. It would thus appear that it was to all intents 

 and purposes a novice in the art of discriminating cater- 

 pillars. The jackdaw having been fed in the morning, at 

 mid-day Miss Clould offered him a larva of the figure-of- 

 eight moth, and she thus reports of liis behaviour : " The 

 bird looked at the larva suspiciously for a long time, and 

 would not take it. Then he seized it, and, on tasting it, 

 shook his head violently, evidently disliking it. He then 

 dropped it, but picked it up and tried it again, shook his 

 head as before, and finally put it down on the floor of the 

 cage and refused to eat it." That the hesitation did not 

 ai'ise from any objection to caterpillars per sc, was shown 

 by the fact that when a smooth green larva was ottered, 

 the bird snapped it up at once and ate it with avidity. 

 On another occasion, with the view of testing whether the 

 pangs of hunger would be a sufficient inducement to over- 

 come this reluctance, and thus to determine whether there 

 was a limit to the degree of protection aftbrded to the 

 caterpillar by its coloration, the jackdaw had been pur- 

 posely left unfed, so that he was very hungry, and begged 

 for food by carrying his empty food vessel and placing it 

 against the bars of his cage. A large larva of the mullein 

 moth was then given him. " At first he refused it, then 

 took it, but dropped it instantly, shaking his head, and 

 never touched it again. He appeared quite subdued for a 

 time, and sat shaking his head and swallowing. Nor 

 would ho take anything else offered him at all for a little 

 while, but finally ate a gooseberry with relish." Two 

 points seem to be substantiated by these experiments ; 

 first, that brilliant aud conspicuous colouring in a cater- 

 pillar is itself deterrent, at least to a jackdaw, and secondly, 

 that this conspicuous coloration is accompanied by a 

 disagreeable taste. Of course, neither of these two means 

 of protection ultimately availed the caterpillar in these 

 particular instances, since it perished from the injuries 

 received by the tasting as surely as if it had been eaten. 

 But though that might be the case in a bird's first 

 experiences of caterpillar diet, a few trials would teach the 

 novice to avoid such caterpillars for the future, and there- 

 fore the sacrifice of the life of a few individuals would 

 contribute towards the salvation of the majority, and 

 would thus ultimately tend to the advantage of the 



