November 1, 1892.] 



KNOWLEDGE. 



205 



sometimes the entire shell is devoured at the first meal. 

 Almost the only regularly recurring excitement is that of 

 changing the skin, a process which may take place some 

 five or six times, the exact number depending upon the 

 species. It appears to be frequently an operation of con- 

 siderable trouble and difficulty, and is preceded on each 

 occasion by a short period of rest and absthience. These 

 moults are not equally distributed through the life of the 

 caterpillar, and the longest interval is that between the 

 last moult as a larva and that which produces the change 

 to the pupa state. 



The danger of attack by insectivorous birds and reptiles, 

 by parasitic insects such as ichneumon dies belonging to 

 the families Ivlineumonidic or Bracunidit, or dipterous flies 

 belonging to the Tucltinuii^, or by rapacious ones such as 

 the fossorial Hymenoptera, many of which provision their 

 nests with small caterpillars, are features in the life of 

 those larvaa that feed in the open, which, together with 

 the disturbing eti'ect of storms, threatening to shake them 

 from their perches, must give a little zest, if the creatures 

 are only able to appreciate it, to an otherwise flat and 

 tame existence. I3ut in order to guard against such 

 dangers, there is very little in the way of active resistance ; 

 indeed, the insects are so dehcately constructed that it is 

 not safe for them to struggle or fight ; the soft-skinned 

 body is kept in a tense condition by the fluid it contains, 

 which is therefore under pressure, so that any little wound 

 would occasion a considerable loss of blood, which would 

 have the double effect of producing the enfeeblement that 

 always follows blood-letting, and lessening the creature's 

 control over its movements by making it flaccid. Hence 

 a little damage to the skin might easily prove fatal, 

 and therefore the caterpillar cannot afford to be very 

 pugnacious, or to defend itself strenuously if attacked. 

 Therefore the means used are mainly of the passive kind, 

 such as are supplied by protective coloration, a clothing 

 of hairs or spines, or the assumption of a particular 

 attitude, and if these fail, the caterpillar has but to submit 

 to its fate. 



In the articles on ants, published in Knowledge some 

 months ago, it was pointed out that some tropical species 

 of ants assume a sort of guardianship over certain 

 caterpillars for the sake of a secretion they yield, which is 

 palatable to their guardians. A very curious instance of 

 this has been recorded by a reliable American entomologist, 

 the insect protected being the caterpillar of one of the 

 " Blues," called Li/cicmi psi'mltin/iolus. The larva was seen 

 on its food-plant, and " on its back, facing towards the tail 

 of the larva, stood motionless one of the larger ants. 

 . At less than two inches behind the larva, on the 

 stem, was a large ichneumon fly, watching its chance to 

 thrust its ovipositor into the larva. I bent down the stem," 

 says the observer, " and held it horizontally before me, 

 without alarming either of the parties. The fly crawled a 

 little nearer and rested, and again nearer, the ant making 

 no sign. At length, after several advances, the fly turned 

 its abdomen under and forward, thrust out its ovipositor, 

 and strained itself to the utmost to reach its prey. The 

 sting was just about to touch the extreme end of the larva, 

 when the ant made a dash at the fly, which flew away, and, 

 so long as I watched, did not return." The disturbance 

 created by the ant's action apparently caused the caterpillar 

 for the first time to reahze its danger, and it immediately 

 began to lash its fore parts from side to side, thus bringing 

 into requisition its only means of defence. 



Many caterpillars are internal feeders, and live within 

 the trunks of trees, or the stems and roots of reeds, grasses, 

 and other herbaceous plants, in the interior of fruits, or in 

 mines between the cuticles of leaves. Here thiy are, of 



course, more out of the reach of then- foes ; lizards cannot 

 get at them at all, while insectivorous birds find it much 

 harder work to reach them, and there is small chance for 

 the ichneumon flies, except for such as are provided with a 

 long ovipositor to be thrust into the burrows. Hence the 

 life of such caterpillars must be far more monotonous and 

 uneventful than that of outside feeders. In particular, 

 their locomotion is much restricted ; they have to tunnel 

 wherever they go, and sometimes, as in the case of leaf- 

 miners, the whole area of their lifelong wanderings does 

 not amount to more than a small fraction of a square inch. 

 Such caterpillars do not possess the special means of 

 protection by which their external-feeding relatives are 

 distinguished ; they are usually naked and whitish, and 

 without adornment, and the walls of their prison-like home 

 are a sufficient safeguard. It is curious that for the 

 clearest indications of intelhgence during lars'al life we 

 must go to the smallest species ; amongst the leaf-rollers, 

 or Tortrices, some of which, such as the green oak moth 

 {TortrLc rj>i(/((?i((), completely strip the trees of their young 

 leaves in early spring, and the Tineae, the minutest of all 

 Lepidoptera, we find some remarkable mstances of con- 

 structive power, as shown in the making of shelters out of 

 rolled-up leaves, or in the cutting out and piecing together 

 of cases for the protection of the hinder part of the body. 

 Some caterpillars, again, are social in habits, constructing 

 a common abode in the form of a web. 



A caterpillar has been called a " locomotive egg," in 

 allusion to the primitive condition of its organization as 

 compared with that of the adult insect. This primitive 

 condition is shown pai'tly in the entire absence of several 

 structural details — such, for example, as wings, which the 

 perfect insect is possessed of — and partly in the more rudi- 

 mentary and less concentrated and specialized form of 

 those that it possesses in common with the adult, when 

 compared with what they will ultimately become ; this 

 characteristic is well shown in the condition of the nervous 

 and reproductive systems. With regard to the former of 

 these, there is in the adult a fusion of parts which are 

 separate in the larva, the number of ganglia in the nervous 

 chain being greatly reduced, while the nerve centres of the 

 head and thorax are much increased in size. With regard 

 to the latter, caterpillars are not sexually mature, and are 

 therefore functionally neither male nor female ; but the 

 reproductive organs are actually present, though in a 

 rudimentary condition, so that usually no difl'erence is 

 discernible externally between those that will produce 

 male insects and those that will produce females. This is 

 not, however, always the case ; sometimes certain portions 

 of the reproductive organs become sufficiently distinct to 

 be able to be seen through the skin, and the separation of 

 the sexes can thus be made ; or agaui, there is a difference 

 in ornamentation which is dependent upon sex — for 

 example, the caterpillars of the vapourer moth (On/ijia 

 ((iitiijiia), a common insect often seen even in the streets of 

 large towns, are of very diff'erent sizes, the small ones pro- 

 ducing males and the larger females, while they difl'er also 

 in the colour of the tufts of hairs with which they are so 

 fantastically adorned. From these details it will be seen 

 that in caterpillars a condition of things is exhibited which 

 would in some other animals be a merely transitory 

 stage in their early embryonic history. On the other 

 hand, the larval stage, which is not unfrequontly the 

 longest division of the insect's life, embraces the whole 

 period of growth, and in fact the insect's actual bulk at the 

 end of its caterpillar career is generally greater than during 

 its subsequent history, the change into the chrysalis being 

 attended with a diminution in size, while, in like manner, 

 during that period, there is a gradual loss of weight, due 



