IIARBWICKE'S SCIENCE-GOSSIP. 



171 



commence again, its one duty of preparing for the 

 great change which it undergoes about the end of 

 June or beginning of July. I have noticed that, 

 when owing to its having been deprived of food, the 

 larva has been compelled to change into pupa before 

 its time, the perfect insect is invariably smaller than 

 is usual after it has been allowed to change in regular 

 course. 



It is always well to keep larva; well supplied with 

 food, as I have found in the case of a number of 

 caterpillars of the large white butterfly {ricris bras- 

 sicce), that when deprived of food, some of them turned 

 into the chrysalis state, and the survivors thinking 

 no doubt that being deprived of their natural food, 

 they were fully justified in resorting to cannibalism, 

 devoured the chrysalides whilst they were yet in a 

 soft condition. This undoubtedly was a neglect on 

 my part which was deserving of reproach, as the food 

 of this species is easily obtainable, consisting chiefly 

 of cabbage-leaves. 



Another difficulty I found, in the rearing of ricris 

 brassicce, was caused by a minute enemy in the shape 

 of an ichneumon fly, with a very black body and 

 yellow legs. This is a persevering enemy, and the 

 larvae breeder may discover at the last moment that 

 a fine specimen, or a batch of specimens, has been 

 lost, owing to the ravages of this insect. He may 

 glance into his cage, as I have sometimes done into 

 mine, expecting to find the caterpillar of yesterday 

 transformed in the chrysalis of to-day, and be sur- 

 prised, and when he knows the result, disappointed, 

 by finding the empty skin of the caterpillar encased 

 in what appears to be a thick web of yellow silk, but 

 which, on a nearer inspection, proves to be a number 

 of small cocoons, out of which, in the course of time, 

 a brood of ichneumons will proceed to commence, as 

 their progenitors had done, a fresh warfare on cater- 

 pillar life. 



The manner in which they proceed is this : — Alight- 

 ing on the back of their victim, they, by means of an 

 instrument formed somewhat like the teeth of a saw, 

 termed an ovipositor, introduce their eggs into the 

 interior of the caterpillar's body ; these eggs in time 

 turn out a number of maggots, who immediately 

 commence a work of devouring their strange habita- 

 tion, carefully avoiding coming in contact with the 

 vital parts. Thus the poor caterpillar, unconscious 

 of its impending fate, goes on eating day by day, only 

 to provide food for the " eaters" inside. When the 

 fulness of time has arrived they eat their way through 

 the skin, and change, as we have seen, into pupae, 

 leaving their victims an empty withered mass. 



Thus it will be seen that the life of the caterpillar 

 does not always terminate in a satisfactory manner. 



A troublesome episode in the career of the larva is 

 the process of changing its skin. A day or so before 

 this moulting occurs, the caterpillar gives up eating, 

 and retires into some quiet corner, where he under- 

 goes this, to him, very painful operation. The old 



skin, becoming too small for the growing body, 

 splits down the back, and the caterpillar, with a few 

 struggles, emerges from it, arrayed in a perfectly new 

 skin. Sometimes, however, this operation proves 

 fatal, and the caterpillar dies during the process. 



Some novices in the art of larvae-breeding seem to 

 think that one kind of green food is quite as suitable 

 as another for the wants of the caterpillar ; but this 

 is not so. Each species has its peculiar food-plant ; 

 and although the caterpillar of Vanessa Jo, Vanessa 

 tirticce, Vanessa atalanta, seem to be equally fond of 

 the nettle, yet if placed on a gooseberry-bush, they 

 would be quite at sea, and would refuse to partake of 

 the gooseberry-leaf. 



And it is worthy of observation that an all-wise 

 Providence has so disposed the perfect insects that 

 they invariably lay their eggs upon, or in close 

 proximity to the food-plant of their species. 



Just a word as to the mode of collecting larvae. I 

 have found a good strong sweep-net, such as sold by 

 Watkins and Doncaster, of the Strand, invaluable in 

 a collecting expedition. The mode of application is 

 simple : — Having come upon a spot covered thickly 

 with vegetation — dead-nettles, etc. — plunge your net 

 into the midst of it, sweeping it from side to side, 

 taking care that the impetus of your second stroke 

 does not throw out of your net the captives made by 

 the first stroke. This will generally be found a 

 pretty lucrative mode of collecting. Another mode 

 is by beating hazel, and other kinds of bushes, with 

 a substantial stick, holding a net or an umbrella 

 underneath, to intercept whatever is dislodged from 

 the bush. 



Morpeth, Northumberland. 



STUDIES OF COMMON PLANTS. 



By E. A. Swan, e.a. 



No. VIII.— THE HOLLYHOCK. 



THE flower is thus composed. Involucre : a 

 whorl of seven or more bracts, and next, a 

 whorl of six or more larger bracts, all set closely. 



Corolla : five petals, and, in the double flowers, 

 generally six. Towards the base, each petal gradu- 

 ally thickens on either side, as shown in Fig. 85 ; 

 and the upper edges of the thickened parts are 

 closely lined with fine hairs. The petals overlap, 

 but leave small openings near the base, between the 

 thickened parts. The opposite sets of hairs, then 

 interlacing, effectually keep out small insects above 

 from the enclosed spaces thus formed, and in which 

 the nectar is secreted, the bracts effecting the same 

 purpose below. 



Column rises from the base, formed by the junction 

 of the thickened parts, and, according to the number 

 of petals, is five-sided or six-sided. 



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