42 



KNOWLEDGE, 



[March 1, 1893. 



poplar, a large number of the larvae were separated into 

 groups, which were placed in different receptacles. Of 

 coui'se in all it was inevitable that there should be a certain 

 amount of green surroundings, because of the leaves of the 

 food plant ; but the circumstances were varied by the 

 introduction of other objects. For example, to give a 

 preponderance of dark surroundings there were introduced 

 a number of very dark twigs from a kind of oak tree, 

 together with stems of other kmds, all dark but of different 

 tints in the different cases. Spills made of dark-coloured 

 paper, and artificial leaves, or natural dead leaves, were 

 also used, being stuck about amongst the food plant. In 

 the case of the light surroundings, there were, besides the 

 leaves of the food plant, green twigs, and spills of white or 

 light-coloured paper. The caterpillars were introduced 

 into these special surroundings when about half-grown, as 

 that was found to be, on the whole, the most susceptible 

 age. The general results of a large series of experiments 

 (Fig. 1.5) were that the majority of those amongst the dark 

 surroundings tended to become 

 darker than when introduced, 

 developing some shade or other of 

 brown — such, namely, as best har- 

 monized with the exact tint of the 

 dark objects used, while in the 

 experiments with light surroimd- 

 ings the reverse was the case, and 

 tbe larviE became pale green or 

 other light colour, some of the most 

 remarkable results being produced 

 where the white spills were used. 

 It thus seems to be established that, 

 in the case of some msects at least, 

 fe \-Ji j W^ ^^^ colour of then- environment 

 \ r* L^ Ka has an important influence in deter- 



mining their own colour. But it 

 must also be admitted that there 

 are many species amongst those 

 experimented upon, which show 

 very little of such susceptibility, so 

 that the final determination of 

 colour in many instances is probably 

 a somewhat intricate matter, and 

 dependent upon many different 

 conditions. 



Eecognizing, however, as we seem 

 bound to do, that the surroundings 

 do constitute a possible factor in determining the colour 

 of the caterpillar, we may even take one step farther 

 and suggest that the general pattern, as well as tbe 

 mere colour of the surroundings, may also be reproduced 

 in the skin of the caterpillar. It is not difficult to call 

 to mind many curious facts illustrating such connection 

 between the pattern of the caterpillar's ornamentation and 

 the prevalent features of its environment. For example, 

 the larvae of the butterflies of the family Satijrida, such as 

 the familiar meadow browns and heath butterflies, which 

 feed on grasses, are striped longitudinally with dark and 

 pale Unes. Now it is obvious that in a spot where a 

 quantity of tall grass is gi-owing, longitudinal lines of 

 shading and colouring, caused by the ribs and veins, stems 

 and leaves of the gi-asses, and the shadows they produce, 

 will be artistically tbe predominant feature ; and then we 

 find that the caterpillars which live in such spots partake 

 of the prevailing style of colour-arrangement too ; while, 

 to put the converse fact, those caterpillars that feed upon 

 broad-leaved plants, in which such longitudinal effects of 

 light and shade will be much less conspicuous, if present 

 at all, are usually found, though still possessing some pale 



FlO. 15.--Larva;of Pqiper 

 Moth (Amph idasis 

 hetiilariaj. A. Green 

 speeiraen on green 

 twig ; B. Brown speei- 

 nieu on brown twitj. 

 (Mter Poulton.) 



longitudinal lines, not to have them so prominent or occu- 

 pying so much of the surface. These can hardly be mere 

 coincidences. 



When oblique stripes are present it is in species which 

 feed on broad-leaved plants ; and as the venation of leaves 

 of this kind is of a different type from that of grasses, the 

 chief veins branching from the midrib at an angle, instead 

 of running more or less parallel to the edge of the leaf, 

 the oblique stripes on the caterpillars have been supposed 

 to be a sort of reflection of the obliquity of the veins of the 

 leaf, especially as there is often present on the caterpillars 

 a longitudinal line as well, just beneath or running through 

 the oblique stripes, suggestive of the midrib of the leaf. 

 However, as it is only in a small proportion of cases 

 amongst those that feed upon plants whose leaves are 

 veined in this way that such ornamentation holds, and by 

 far the greater number show no trace of diagonal lines, the 

 case for imitation is a far less strong one than that of the 

 longitudinal striping. The most remarkable instances of 

 oblique striping are to be found amongst the caterpillars 

 of the hawk moths, many of which exhibit it in the highest 

 degree, thereby greatly enhancing their beauty. Nothing 

 can be more harmonious, for instance, than the coloration 

 of the larviB of the privet hawk moth, one of the com- 

 monest of the group ; in this insect the ground colour is a 

 beautiful tint of green, and the stripes, which are seven in 

 number on each side, are white edged with a band of the 

 purest lilac on the upper mai'gin. The huge caterpillar of 

 the death's head moth is another very remarkable instance ; 

 its stripes are pale blue on the back, but farther down they 

 deepen into black and are edged with yellow. 



But the greatest interest attaches to that peculiar style 

 of ornamentation called " eye-spots." These are large 

 circular patches of concentric rings of colour, which occur 

 only in a very few caterpillars, and irresistibly suggest the 

 eyes of some vertebrate animal. The true eyes of the 

 caterpillar, it will be remembered, are practically invisible 

 except on a close inspection, and there is nothing, therefore, 

 to compete with these spots or neutralize their effect. By 

 far the best illustration of this type of ornamentation that 

 we meet with in this country is to be seen in the larva of 

 the elephant hawk moth {('hierocawjui cljicnor) (Fig. 16). 

 It feeds on the 

 common hairy 

 willow-herb of 

 damp ditches 

 and river sides, 

 a plant which, 

 from its gay 

 clusters of 

 large pink 

 flowers and its ^j^ ig_ 

 habit of grow- 

 ing in dense 



clumps to the height of four or five feet, is one of the first 

 of summer wild plants to attract attention, and must be 

 well known to everybody. The caterpillars may also 

 sometimes be found in gardens feeding on fuchsias. 



These larvie are interesting in many respects. They are 

 of the type known as dimorphic, i.e., like those of the 

 pepper moth they have two varieties when fully grown, a 

 green one and a brown one, a circumstance which, 

 according to Mr. Poulton, betokens a ready adaptability 

 in the insect to colour changes in its surroimdings. At 

 first, however, they are all green, and during the early 

 part of their life they remain amongst the leaves of their 

 food plant when not eating, thereby availing themselves of 

 the concealment afforded by the harmonizing of their 

 colour with that of the foliage around them. But when 



-Larva of Elephant Moth {CAnerocampa 

 elpenor) in its last stage, slightly reduced. 



