AN ENCYCLOPAEDIA OF HORTICULTURE. 



183 



Insects continued. 



of the others, which, despite this aid, are often but 

 too wide-spread and serious. 



Space will not here permit of more than a very brief 

 sketch of some of the leading points in the structure 

 and life-history of the class and of its leading orders, 

 with a mere indication, in the most general terms, of 

 the more conspicuous damage done by them, and of the 

 means of remedy generally applicable; but fuller infor- 

 mation will be found plentifully scattered through this 

 work under the various headings referred to below. 



The word " Insect " literally means any 

 animal which has the body so divided as 

 to seem cut into successive parts, usually 

 resembling rings of hard substance, con- 

 nected by soft skin. The name has been 

 used to include all the animals with bodies 

 resembling a row of joints, even Worms 

 having been at one time included among 

 Insects, along with Spiders, Mites, Crabs, 

 Woodlice, and Centipedes. At the present 

 time, the name is confined to a considerably 

 smaller group of animals the true Insects 

 though some authorities still include with 

 these the other groups named above, except 

 Worms. In this restricted sense, the class 

 of Insects is composed of animals that 

 possess a jointed body made up of a num- 

 ber (twenty or twenty-one) of rings of 

 horny substance (chitine), connected by skin, so united 

 as to form three great divisions in the body, viz., the 

 head, the thorax, and the abdomen; that have antennae, 

 or feelers, on the head, and three pairs of horny jointed 

 legs, and usually two pairs of wings, on the thorax; 

 that breathe by tubes (tracheae) all through the body 

 and limbs, which tubes open on the surface of the body 

 by small holes (spiracles); and that, in course of growth, 

 pass through a succession of changes (metamorphoses), 

 beginning with the egg, and going on through the stages 

 of larva and pupa (chrysalis), before assuming the per- 

 fect condition (imago), in which alone they present 

 all the characters enumerated above. This series of 

 changes may be of two kinds. In one, the larva, on 

 emerging from the egg, resembles the mature Insect in 

 form, and differs from it only in size, and in the entire 

 absence of wings ; while the pupa differs from the mature 

 Insect only in the wings, though indicated, being small and 

 rudimentary. Both larva (see Fig. 314 ) and pupa are 

 also sexually immature. This kind of metamorphosis is 

 said to be incomplete. Complete metamorphosis differs 



FIG. 289. LARVA OF SMALL CABBAGE BUTTERFLY. 



Insects continued. 



scarcely showing even a trace of a head. Such larvaa 

 are familiar to everyone under the name of maggots or 

 grubs, e.g. those of Bees, Flies, &c. (see Fig. 311). The 

 pupae of Insects that undergo a complete metamorphosis 

 are not able to move about or to feed, but remain 

 helpless for a longer or shorter period, while changes 

 are going on within, which result in the development of 

 the perfect insect (imago), showing all the distinctive 

 characters already set forth. These quiescent pup 

 differ much from the larvae (see Fig. 309), as they show the 



FIG. 290. LARVA OF LEOPARD MOTH. 



from this in the larva (see Figs. 289, 290, and 291) being 

 quite unlike the mature Insect. Very generally, it re- 

 sembles a worm in its form. It may have a distinct 

 head, and the rings of the body, though like one another, 

 may differ in the three immediately behind the head 

 each bearing a pair of horny jointed legs, while those 

 of the hinder part of the body may bear skinny suckers 

 (prolegs) the number varies considerably, and they 

 may be quite absent. Larvae of this type (see Fig. 291) 

 are called Caterpillars, and are met with among the 

 Butterflies, Moths, and Sawflies. Another group of In- 

 sects, in the larval state, are footless creatures, frequently 



FIG. 291. LARV.B OF ROSE-LEAF SAWFLY. 



future limbs (antennae, legs, and wings) of the imago, 

 though these parts are still useless, and of very small 

 size. The Butterflies and Moths, while pupae, have the 

 whole body enveloped in a hard crust, which binds down 

 all the parts immovably to the body, leaving only a 

 slight power of movement in the hinder rings. When 

 the pupa is helpless, its safety is generally provided 

 for by the larva forming a cell or cocoon of silk, 

 earth, or other material, compacted with a cement from 

 its mouth, in which the pupa lies concealed till the 

 imago breaks out from it, and crawls to the outer air, 

 with wings at first crumpled and useless, but soon ex- 

 panding and becoming firm to carry it in flight through 

 Jfche air. Whatever the degree or kind of metamorphosis 

 undergone by it, the Insect, in its progress from the egg 

 to maturity, grows frequently with enormous rapidity. 

 The outer coat of the body is too rigid to allow of the 

 corresponding extension in it; but the difficulty is met 

 by the larva several times (four times or oftener) throw- 

 ing off its skin. The old skin separates from the body of 

 the larva, it splits along the back in front, and the larva 

 wriggles its way out, frequently with a skin of a very 

 different colour from that in which it had previously 

 shown itself. In like manner, the skin of the pupa 

 bursts to set free the imago. 



The sudden and mysterious appearance of certain 

 kinds of Insects at one time led to the belief that they 

 must be produced by spontaneous generation from dead 

 and decaying substances; but the progress of accurate 

 researches into their life-histories has proved conclu- 

 sively that they always originate from parents, though 

 at times, in the case of certain Insects, e.g., several of 

 the true Gall-flies of the Oak-tree, the parents and the 

 immediate offspring may differ considerably in appear- 

 ance. The females produce eggs, except in a few groups, 

 such as the Aphides, in which the young Insects may be 

 brought forth, not sexually by eggs, but by a process 

 of budding. In the case of a few other Insects, the 

 eggs are hatched while still within the body of the 

 mother, which thus gives birth to living young or larvae. 

 The fact that Insects are always produced from parents, 

 renders it of the utmost importance, when dealing with 

 the injurious species, to become familiar with the habits 

 of the females as well as of the larvae, which latter are 

 usually the destructive agents, and are therefore the more 



