December 1, 1892.] 



KNOWLEDGE 



227 



further, nor does it seem to be in the least degree an un- 

 palatable morsel. 



But as a few actual experiments are worth more than 

 any amount of theorizing, we are fortunate in having 

 records of the observed behaviour of this insect in situa- 

 tions of danger. Mr. Poulton placed one of them on a 

 table and caused it to assume the terrifying attitude ; he 

 then drew the attention of a marmoset to it, but though 

 this little monkey is very fond of caterpillars, and would 

 seize with avidity those of an ordinary appearance, it 

 hesitated for some time before proceeding to the attack, 

 and when at last it summoned up sufficient corn-age, 

 advanced in a very cautious manner. A lizard also 

 manifested hesitation in a similar case, although, being 

 a less intelligent animal, and therefore presumably less 

 imaginative, it was not so strongly affected as the monkey. 

 In this case the attitude was sulSciently iutiuential to 

 cause hesitation on the part of the marmoset, though it 

 did not succeed in saving the insect's life. But possibly 

 the result might have been different in the wild and open 

 state of nature, where there would have been many other 

 opportunities of obtaining food, and the preliminary 

 reluctance might have developed into complete avoidance, 

 and thus have been the means of preserving the cater- 

 pillar's life ; and though no such foes as monkeys of any 

 kind would encounter it in a native condition in this 

 country, it is not improbable that birds, which would be its 

 chief vertebrate enemies, might be daunted in the same 

 way as the marmoset. 



It has also been suggested that the spider-like attitude 

 may be intended to frighten away ichneumon tlies as well 

 as vertebrate foes, not that parasites belonging to this 

 group never attack spiders, but that they seem, as a rule, 

 inclined to avoid them, and in fact they are very seldom 

 found caught in spiders' webs. And fiu-ther, it has been 

 pointed out that the lobster moth caterpillar has a certain 

 peculiarity of markmg which would tend to protect it from 

 ichneumons, even if they were not deterred by its fautasiic 

 appearance. On the first and second segments behind 

 those to which the legs are attached, there is on each side 

 a small pouch-like hollow of an intensely black colour, 

 but capable of concealment by means of a triangular flap 

 of skin. When the caterpillar is at rest, the black spots 

 remain covered, but when irritated and alarmed the flap 

 is drawn back and the black marks made to become con- 

 spicuous. Now, as ichneumon flies are apt to make small 

 wounds on caterpillars, not only by their ovipositors, but 

 also by their jaws and claws as they hold on trying to 

 effect oviposition, and as the blood issuing from these 

 wounds invariably forms a black clot, it is suggested that 

 the appearance of these black spots on the lobster cater- 

 pillar may give the idea to an ichneumon contemplating 

 attack that the insect has already been selected and has 

 received the indwelling parasite, so that it is not available 

 for the reception of another. It is much to be desired 

 that experiments on this score could be tried with 

 ichneumon flies, but for this we must be content to wait. 

 Even with these beautiful adaptations, if they be such, 

 we do not exhaust the means of defence possessed by this 

 remarkable insect. Its brownish colour almost exactly 

 resembles that of a dried and curled-up beech leaf, that 

 being one of the trees on which it feeds, while in the time 

 of its larval life, the late summer and autumn, such leaves 

 would be likely to be about : and again, iis long legs have 

 been pointed out by Mr. Poulton, not only to be suggestive 

 of spiders, but also, when folded up in ;he position of rest, 

 to resemble very closely the little bunt lies of brown scales 

 or stipules that hang down from the leaves of the beech 

 tree. So this insect seems to be a special pet of Nature, 



the one fraU child which is not fit to rough it, and to 



secure whose welfare, therefore, unusual precautions are 

 required, its special need having led to the acquisition of 

 quite special means of protection ; and indeed, notwith- 

 standing this, still it is not able to flourish and multiply 

 to any great extent, for it is never other than a rare 

 insect. 



The six thoracic legs, as might be inferred from their 

 form, are not the only, nor indeed the chief, means of 

 progression possessed by caterpillars. Some of their hinder 

 segments are furnished with pairs of fleshy and highly 

 elastic pillar-like appendages, called claspers or prolegs, 

 which are their chief, and sometimes their only means of 

 support when they are on their food-plant. In aU the 

 larger species these organs have great grasping power, 

 which is due to. numbers of little hooks round their edge 

 (Fig. 4), by aid of which the caterpillars can hold on so 



tightly that they 

 will often endure 

 damage rather than 

 relax their grasp, 

 the claspers them- 

 selves meanwhile 

 remaining firm and 

 tense by reason of 

 the blood which is 

 Fig. 4. — Microscopical preparation, showing forced into them and 

 hooks on proleg of Caterpillar of Lime i 4. ii j 



Hawk Moth, maVified 16 diameters. ^^^pt there under 



pressure. The most 

 common number of these equivalents of legs is five pairs, 

 which gives the insect, together with the three pau-s of 

 thoracic legs, a total of sixteen points of contact with its 

 base of support when at rest. One pair of prolegs is 

 situated on the last segment ; on the two segments in 

 front of this, for a reason we shall see presently, there are 

 none ; and then the remaining four pairs occur on the 

 next four segments ; hence, rememberiog that there are 

 in all twelve segments besides the head, it follows that 

 between the last pair of true legs and the first pair of 

 prolegs there are again two segments unprovided with 

 appendages. 



\\ hen a caterpillar thus equipped is resting stretched 

 out at full length along a leaf or stem, it would generally 

 hold on by all the sixteen legs; but some species rest 

 clinging by the prolegs alone, the front part of the body 

 being then elevated into the air. Special attitudes of rest 

 are often characteristic of different groups. Thus, for 

 instance, the caterpillars of several of the " hawk moths " 

 elevate the front part of the body, and giving it a 

 graceful curve, rest with it kept steadily, in a state 

 of rigidity, in that one position, thus reminding one of 

 the contour of an Egyptian sphinx. Amongst British 

 insects this is best seen in the common privet hawk 

 moth {Sphiti.r liiimtri), which derives its generic name from 

 the circumstance. After this caterpillar has reached its 

 mid career, the sphinx-Uke attitude (Fig. 5) is often 

 assumed as the ordi- 

 nary position of rest, 

 whence it would seem 

 that some other reason 

 should be sought for 

 it than that of attempt- 

 ing to deter possible 

 assailants, though con- 

 ceivably the striking 

 appearance of the 

 caterpillar in this 

 position might lead an animal which wished to make a 

 meal of it to think twice before pouncing upon so stately 



Fig. o. — Caterpillar of Privet Hawk 

 Moth, showing sphinx attitude, natura I 

 size (after Poidton). 



