Insects] 



MUSEUM OF ANIMATED NATURE. 



363 



a (icubf, as the experiments of Reaumur and De Geer 

 satisliictoiily prove ; and in some instances, if not in 

 all, the mouths of the spiracles are furnished with 

 ciliary valves, which are closed immediately if the 

 pupa be immerged in water, but open when it is 

 taken out. 



Fig. 3365 shows the structure of this apparatus : 

 a is the mouth of a spiracle with the valve open ; 

 6, the same wi.th the valve shut. 



Vie need scarcely say tliat far more definitely 

 than in the caterpillar the parts of the perfect insect 

 can be demonstrated in the pupa, even where they 

 are not manifest externally. In the moths and 

 butterflies the insect enclosed in the pupa-case is 

 very palpable. Fig. 3566 represents the leaf-like 

 Lappet-moth (Gastropacha quercifolia) : a, the pupa 

 removed from the cocoon ; b, the moth seen on 

 the under side with its feet folded up ; c, a side 

 view of the same. 



The pupa has a close resemblance to an Egyptian 

 mummy in its inner case ; the feet are folded over 

 the breast, and the wings, which in the perfect insect 

 are so ample, are compressed into a small compass, 

 and these and the antennae have all their respective 

 sheaths. The haustellum of this moth is in a rudi- 

 mentary state, but the palpi project horn-like from 

 the forehead. In the beautiful peacock-butter- 

 fly, of which the caterpillars are abundant on the 

 nettle, the chrysalis is angular ; two angular points 

 encase the eyes, while the wings lie beneath four 

 lateral angles, of which the uppermost on each side 

 forms a sort of shoulder. The limbs, the antennae, 

 and the sucker or haustellum run longitudinally 

 down the breast. If a pupa in an advanced stage 

 be selected, the thin membranous pupa-case may 

 be removed by careful management, and the dif- 

 ferent members traced out with little difiiculty. 

 The wings will be found soft, crumpled, and humid, 

 and the powdery down of fine scales which covers 

 them will be scarcely visible, nor will the rich 

 colouring be displayed. Already, however, are the 

 limbs firm and capable of being moved about, the 

 proboscis capable of being curled up, and the an- 

 tennae of being put into action. 



Fig. 3567 shows — a, the under side of the chrysa- 

 lis of the peacock-butterfly ; b, the wings, and an- 

 tenna; traced out from the same ; c, the perfect 

 insect, Vanessa lo, fully developed. 



The period at which pupje come to maturity is 

 no doubt greatly influenced by temperature, though 

 in all probability there are other circumstances 

 which operate in hastening or retarding the process. 



At first the body is almost liquid or of a soft and 

 pulpy consistence, and consolidation and firmness 

 are gradually acquired. According to Swammerdam 

 these results are effected by evaporation ; and in 

 accordance with this view Kiiby and Spence ob- 

 serve that " it is quite plain that this necessary 

 transpiration, other circumstances being alike, must 

 take place sooner in a small than a large pupa. 

 Since the more speedy or more tardy evaporation 

 of fluids depends upon their exposure to a greater 

 ' or less degree of heat, we might, a priori, conclude 

 that pupEB exposed to a high temperature would 

 sooner attain maturity, even though larger in bulk, 

 than others exposed to a low one ; and this is the 

 fact. The pupa of a large moth which has assumed 

 that stage in the early part of summer will often 

 disclose the perfect insect in twelve or fourteen 

 days; while that of the ichneumon, not one hun- 

 dredth part of its size, that did not enter this state 

 till late in the autumn, will not appear as a fly for 

 seven or eight months. But this is not the whole. 

 , The very same insect, according as it has become a 

 pupa at an earlier or later period of the year, will 

 ' at one time live but a few weeks, at another several 

 months in that state." 



Reaumur pursued a series of experiments by sub- 

 jecting the pupae of different butterflies and other 

 insects to different degrees of heat and of cold, and 

 found that in the hothouses of Paris he could cause 

 ; in some the development of the perfect insect in 

 ten or twelve days during the middle of winter, and 

 i in others in three, four, five, or six weeks ; and that 

 the butterflies were healthy and laid eggs. On the 

 contrary, he found that he could prevent pupa; that 

 , would naturally appear as perfect insects in July, 

 from undergoing any change, by placing them in 

 unnaturally cold situations. Some pupae, formed in 

 August, 1733, he kept thus torpid from January 

 throughout the summer and autumn of 1734, and 

 still on to August, 1735 ; and though they were liv- 

 ing and healthy, they had not undergone their trans- 

 formation. These and many other experiments 

 I certainly demonstrate the fact that the change of the 

 pupa is accelerated by warmth and retarded by cold ; 

 but though the pupa may exhale vapour from its 

 spiracles, we cannot see how evaporation is to ef- 

 fect a perfection of parts which in all other animals 

 results from vital operations. We repeat that 

 we know not how evaporation can complete the 

 changes which the vital powers of the system have 

 jbeen carrying forward. Moreover, though we ad- 

 I Vol. II. 



mit the effects of temperature, yet temperature 

 alone will not produce uniform effects. We are in- 

 formed by Mr. Marsham (' Linn. Trans.' vol. x.), that 

 Mr. Jones of Chelsea in one of his excursions cap- 

 tured a female specimen of the spotted muslin-moth 

 (Diaphora mendica), which laid a number of eggs. 

 From these he procured thirty-six caterpillars, which 

 he fed till they spun their cocoons and became pu- 

 pae; all were exposed to the same temperature, but 

 at the usual season only a third of them produced 

 moths, and he concluded that the rest were dead : 

 but the second season, twelve more moths to his as- 

 tonishment made their appearance ; and the remain- 

 ing twelve became evolved the third season, and 

 were active and healthy. The same circumstance 

 has been observed in the instance of other pupae. 



The exit of an insect from its pupa-case is a most 

 interesting spectacle, and one which every person 

 has the opportunity of witnessing. Immediately 

 previous to this event, the frame of the pupa seems 

 convulsed, and the pulsation of the dorsal vessel 

 quickened; it is now easy to perceive that the en- 

 closed insect, say a butterfly, is freeing itself within 

 its case, or puparium ; it presses forwards and a 

 cleft IS made in the back near the head, and through 

 the aperture emerges the liberated butterfly. The 

 antenUEe and limbs are drawn out of their cases ; 

 the wings are crumpled, wet, and soft, of a thick 

 substance, and capable of being stretched out, which 

 cannot be done with the wings when perfect and 

 hardened. Awhile it rests, as if exhausted, but soon 

 the fluids are violently agitated and impelled through 

 the wings, air from the respiratory apparatus rushes 

 down the tubular nervures,the limbs are in motion, 

 the wings quiver and become extended as they 

 yield to the impetus of the aerial and circulating 

 fluids; their wrinkles vanish more and more, and 

 the colours, spots, and markings develop and 

 strengthen, displaying their elegant arrangement 

 and brilliancy of tone. In about half an hour the 

 recently wet and drooping wings have acquired their 

 due firmness and expansion ; and now, fanning the 

 sunny air, it fearlessly commits itself to an untried 

 element ; disdaining the coarse herbage on which 

 it had formerly fed, it seeks the flowers and sips 

 their honeyed sweets. 



Instances of deformity in insects are not of rare 

 occurrence. From injuries received by the cater- 

 pillar or pupa, and sometimes, perhaps, from origi- 

 nal malformation, one or more or all the wings 

 never become expanded, and the insect remains a 

 cripple, scarcely able, or even not able to fly ; ex- 

 clusive therefore of accidents to which it must be 

 peculiarly liable, privation of food soon terminates 

 its existence. Fig. 3568 represents a specimen of 

 the small tortoise-shell butterfly : a (Vanessa Urticte), 

 with one wing imperfect ; b, the brown-tail moth 

 (Porthesia auriflua), with shrivelled wings ; and c 

 (Vanessa Urticae), with unexpanded wings. 



From the caterpillars and pupae of the Lepidop- 

 tera let us turn to those of other insects, many of 

 which are very interesting. 



The larvae or maggots of flies (Muscidas), unlike 

 those of most insects, never change their skin ; 

 they suffer no moult, not even when they assume 

 the pupa state. If we take the maggot of the com- 

 mon blow-fly (Musca vomitoria) as an example, we 

 shall find that having attained to a proper develop- 

 ment without any moult, it leaves the putrescent 

 animal matter on which it has been feeding, and 

 buries itself a few inches deep in the soft earth ; 

 here it becomes contracted in length, increased in 

 circumference, hard, firm, and tough, with skin like 

 thin parchment, and of a dull red ; it is now in its 

 pupa state, and resembles in form an elongated oval. 

 When the perfect fly escapes from this envelope, it 

 leaves behind the mandibles it possessed while a 

 caterpillar, and which are no longer needed ; they 

 remain in the inside of the puparium. 



Fig. 3569 represents — a, the pupa of the blow-fly ; 

 h, the same, magnified ; c, the head of the pupa, 

 opened to show the cast mandibles; d, the pupa of 

 a two-winged fly (Syrphus). Fig. 3570 shows — a, the 

 newly-hatched blow-fly, magnified, with the wings 

 crumpled, wet, and pulpy ; and b, the same with the 

 wings dry and fully expanded. 



The larva of the Syrphus (Fig. 3571, the perfect 

 insect) feeds upon aphides, which it destroys in 

 great numbers; unlike the larva of the blow-fly, it 

 does not when about to become a pupa bury itself 

 in the earth, but applies by means of its mouth a 

 drop of tenacious gluten to a leaf or twig, and on 

 this presses down its body, which soon becomes im- 

 moveably fixed, and assumes the pupa state. The 

 larva is destitute of eyes, and, as Kirby says, it fixes 

 itself by its tail and gropes about on every side till 

 it comes in contact with an aphis ; this it instantly 

 transfixes with a sort of trident or three-pronged re- 

 tractile organ ; and elevating it, so as not to be dis- 

 turbed by the victim's struggles, soon devours it. 



The larvae of the lace-winged flies (Hemerobius) 

 are still more destructive to aphides. They are ac- 

 tive, and armed with two crescent-shaped jaws 



which are tubular ; these they plunge into the body 

 I of the aphis, and through Ihem imbibe its jui-cea, 

 leaving nothing but a withered skin. Nothing can 

 be more dissimilar in appearance than the delicate 

 fluttering lace-winged Hemerobius and its vora- 

 cious larva. 



Fig. 3.572 represents — a, the Hemerobius, or lace- 

 winged fly ; b, the larva of the same, magnified ; c, 

 syrphus ; d, the larva of syrphus devouring the 

 aphides of the elder ; e, the head, magnified to showr 

 the mouth. 



Among larvae remarkable for their habits may be 

 noticed the ant-lion, or larva of a neuropterous fly, 

 Myrmeleon formicarium, allied to the dragon-flies. 



The larva is of a depressed form and grey colour, 

 not much unlike a woodlouse in genera! aspect, but 

 larger and more triangular ; it has six legs, and a 

 pair of formidable jaws, resembling a pair of calliper 

 compasses, and these are perforated and tubular, 

 being adapted for seizing ants, upon which" it chiefly 

 preys, and imbibing their juices. It is slow and re- 

 trograde in its movements, always walking back- 

 wards ; but its slowness is more than counter- 

 balanced by the cunning and artful plan it adopts in 

 order to secure its victims. This larva is found in 

 sandy places, where the sand is fine, and though not 

 known to exist in England, is common in some parts 

 of France. Mr. J. O. Westwood observed it in the 

 Pare de Belle-Vue near Paris, where its cells were 

 at the foot of a very high bank of exceedingly fine 

 sand. It is in such sand that it constructs a funnel- 

 shaped pitfall, at the bottom of which it lies mo- 

 tionless, in wait for its prey, covered entirely with 

 sand, excepting the jaws, which are exposed and 

 spread open on the sand, so as to be scarcely visible. 

 Here then it lies in wait for its prey. If alarmed, 

 says Mr. Westwood, it takes a step backwards, bury- 

 ing the jaws; "but when an insect falls into the 

 hole, the jaws are instinctively and instantaneously 

 closed, and the insect seized by the legs, wing, or 

 body, just as it may chance to fall within the reach 

 of the ant-lion's jaws. If, however, the insect be not 

 seized, but attempts to escape, no matter in what di- 

 rection, the ant-lion immediately begins twisting 

 its head about, and shovelling up the sand with the 

 greatest agility, jerking it about on each side and 

 backwards (but never forwards, as misrepresented 

 in some figures), until the hole is made so much 

 deeper, and such a disturbance caused on the sides 

 of the hole, that the insect is almost sure to be 

 brought down to the bottom, when it is seized by 

 the ant-lion ; which immediately endeavours to draw 

 it beneath the sand ; if it be very boisterous, the ant- 

 lion beats it about, firmly holding it with its jaws, 

 until it is too weak for further resistance. Hence 

 as the head of the ant-lion is immersed in the sand, 

 it is evident that the accounts given in popular works 

 of the instinct by which it throws the sand exactly 

 in the direction of the escaping prey are not quite 

 correct ; the act of throwing up the sand, when an 

 insect has fallen into the pit, and attempts to escape, 

 having evidently for its chief object that of making 

 the pit deeper, and more conical, and therefore 

 more difficult of ascent." Its mode of making this 

 trap is as follows: — closing its jaws, it forms them 

 into a kind of shovel, the sharp edges of which it 

 thrusts laterally into the sand on each side of the 

 head, and then with a jerk dislodges the sand, and 

 thus it proceeds till the cavity is excavated. When 

 moving from pl.ice to place, it works its way in a 

 spiral direction, pushing itself backwards and 

 downwards into the sand, the head being carried 

 horizontally and the back much arched : in this 

 manner, mole-like, it travels, forming little mole- 

 hills in the sand, where its jaws are seen emerging. 

 " It does not," says Mr. Westwood, "appear to me 

 that this retrograde motion has anything to do with 

 the actual formation of the cell, since, as soon as it 

 has fixed upon a spot for its retreat, it commences 

 throwing up the sand with the back of its head, 

 jerking the sand either behind its back or on one or 

 the other side." The ant-lion therefore burrows, as 

 well as makes pits. When about to assume a pupa 

 condition, it constructs a globular- cocoon of fine 

 sand, lining it with silk, and in about three weeks 

 the perfect insect emerges. 



Fig. 3573 represents the larva of the ant-lion, mao-- 

 nified, with a perfect trap. The larva is also shown 

 in the act of descending into the sand. Fig. 3574 

 shows the ant-lion's pitfall in an experimenting box. 

 Fig. 3575 represents— a, the perfect insect, Myr- 

 meleon formicarium ; b, the head, magnified to show 

 the calliper-formed mandibles; c, the pupa; rf, the 

 pupa escaping from its cocoon. 



We have said nothing hitherto respecting the 

 changes which the larvae of coleopterous insects 

 undergo, and we now adduce a few examples, upon 

 which lo offer some remarks. 



The larva; of the Coleoptera differ from each other 

 in form and habits, as do the perfect insects; and 

 some ofthem are greatly injurious, and perhaps none 

 in our island more so than those of the chaffer- 

 beetle, Melolontha vulgaris, a common but liand- 



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