184 



THE DICTIONARY OF GARDENING, 



Insects continued. 



generally observed by gardeners and agriculturists. Such 

 a knowledge frequently enables us to devise means of 

 warding off the damage that would otherwise be un- 

 avoidable, and of assailing the destroyers in the most 

 effective way. 



The following details of structure have reference only to 

 mature Insects: 



Mouth. In its essential structure, the mouth consists 

 of certain parts, six in number, though some of them 

 bear appendages. These parts may undergo great modi- 

 fication, and may be adapted to very different uses, so as 

 to be hardly recognisable when compared with the mouth 

 of one of the more typical forms. The chief modifications 

 will be treated of under the various groups of Insects ; 

 it is here only necessary to describe the parts of the mouth 

 of a Beetle, selecting this as a type because of all the 

 parts of a fully-developed mouth being well seen in 

 Beetles. In them, the mouth is formed by an upper 

 lip (labrum), two pairs of jaws working horizontally 

 like the blades of scissors (called mandibles and maxillae, 

 or upper and lower jaws respectively), and a lower lip 

 (labium). The mandibles are specially adapted for cutting 

 the food to be taken into the mouth. The maxillae are 

 not so strong, and often bear tufts of hair to serve as 

 brushes. Each also bears a jointed body (palpus), which 

 seems to serve as a sense-organ. The lower lip bears a 

 pair of similar jointed bodies (labial palpi). 



Limbs. The middle division of the body (thorax) bears 

 the limbs, viz., three pairs of jointed legs on the lower 

 surface or breast, and two pairs of wings, attached to the 

 upper surface of the two hinder of the three rings of which, 

 closely consolidated, the thorax is made up. The legs 

 are generally present, though, in some Insects, one or more 

 pairs may be ill-developed, or even entirely absent. They 

 vary in relative size, and in the number of parts of which 

 they are made up ; but they are of less importance in 

 giving characters for the orders than are the wings. The 

 latter organs, in their typical condition, e.g., in Hymeno- 

 ptera or in Lepidoptera, are two pairs of broad membranes, 

 supported upon nervures traversed by breathing-tubes 

 (tracheae). The upper or front pair almost always exceed 

 the lower or hind wings in size and in complexity of 

 neuration, but resemble them as regards texture and general 

 appearance. In several groups, however, this typical 

 structure is departed from, as will be more fully stated 

 below. Not a few Insects either have the wings small 

 and utterly inefficient (as the female Winter Moth, see 

 Fig. 294), or altogether absent (as Fleas and many other 

 parasitic Insects). 



Periods of Destructive 'Activity. As a general rule, 

 the larvae, during their rapid growth, are far more 

 hurtful to vegetation than are the perfect Insects ; in 

 fact, certain of the groups of Insects are unable, in 

 the perfect state, to feed upon plants, save by sucking 

 up the nectar or honey contained in the flowers, e.g., the 

 whole group of Lepidoptera. Yet these same Insects, 

 in the larval stage, were once provided with strong jaws, 

 well fitted to out their food, and then probably fed vora- 

 ciously upon their food-plants. But among the groups 

 provided with a mouth suited for chewing (e.g., Beetles 

 and Orthoptera), or for puncturing the tissues of plants 

 and sucking the juices (Hemiptera, particularly Aphides), 

 the perfect Insects may be almost as destructive as the 

 larvae ; indeed, some kinds are not injurious to man ex- 

 cept in the mature condition. 



General methods of prevention and of remedy against 

 damage from Insects, may be treated of here ; but 

 details as to these practices must be sought under 

 the special headings. The methods employed to pre- 

 vent attacks must depend on the habits and modes 

 of life of the Insects to be dreaded. Of course, the 

 destruction of the creatures, either as larvae, pupae, or 

 mature Insects, before they have laid their eggs, is the 



Insects continued. 



most certain means. This may be effected either by 

 direct efforts, such as hand-picking, or applications of 

 poisonous solutions or gases to them; or else and pro- 

 bably with greater, if less apparent, success by making 

 use of the natural means of checking their undue in- 

 crease. Among the most efficient of these natural means 

 are birds and parasitic Insects, both of which destroy 

 vast multitudes of the more hurtful kinds in all their 

 stages. Much has been written, and earnest have been 

 the disputes that have been waged, regarding the relation 

 of birds to agriculture and to gardening. While some 

 writers have represented them as frequently most de- 

 structive to the crops and to fruit-trees, others have as 

 strenuously upheld their great value as natural guardians 

 of these crops and fruit-trees from the ravages of swarms 

 of Insect foes. In these, as in so many other disputes, 

 the truth probably lies between the extremes : but, while 

 admitting, as we must admit, that birds are, at certain 

 times of the year, more hurtful than beneficial to farmers 

 and gardeners, yet the danger from them at these times 

 may be comparatively easily guarded against ; while the 

 benefits conferred by them, during the rest of the year, 

 are so great as far to outweigh any damage done by 

 them. It must be remembered, moreover, that injury 

 is done only by those birds that feed on fruits or seeds, 

 such as blackbirds, sparrows, and many finches ; or on 

 roots or tubers, such as rooks ; and that even these 

 birds almost all feed largely on Insects also. On the 

 other hand, many species of slender-billed birds may be 

 said to live exclusively on Insects throughout the year, 

 or such part of it as they spend with us. Some birds, 

 like the bullfinch, are in the habit of pulling off the young 

 buds of the fruit-bearing bushes and trees ; but this 

 seems to be done in the search for larvae hidden in 

 the buds, and which, if left in them, would destroy 

 them in any case. In like manner, the apparent injury 

 done to trees by woodpeckers boring into the trunks, is 

 not really such, as the holes are bored by the bird to 

 reach and to extract the larvae of Insects hidden away in 

 tunnels in the wood, or between the wood and the bark, 

 and which, if left there, would have done no less injury ; 

 while, if they had reached maturity, they would have re- 

 produced their kind, to the further detriment of the 



Even more efficient than the birds, in reducing the 

 numbers of the injurious kinds of Insects, are the parasitic 

 species of Insects ; though, from their small size and unob- 

 trusive habits, they are readily overlooked, and the work 

 done by them undervalued. Among these, some devour the 

 Insects or suck out their juices as food. As examples of 

 these may be noted the Ground Beetles, and the larvaa of 



FIG. 292. LARVA OP LADYBIRD. 



the Ladybird Beetles (see" Fig. 292) and of the Lacewing 

 Flies, which devour the Green Flies, or Aphides, in myriads. 

 Other insects (e.g., some Solitary Wasps) carry off small 

 Caterpillars, &c., to serve as food for their offspring. But 

 far more important than even these are the parasites that 

 deposit their eggs upon or in the body of some Insect, 

 generally a larva, there to disclose the grubs. The latter 

 live in the interior of their host, eating the fat, but leaving 

 untouched the vital organs, till at last, when growth has 

 been completed by the parasites, they either form cocoons 

 inside its body, or else burrow out through the skin, 

 to become pupae in some concealment, where, though 

 helpless, they may remain safe. True parasites of this 

 latter sort belong, with rare exceptions, to the Diptera or 



