108 MEANS FOR ARRESTING THE PROGRESS OF 



348. Besides mammalia, birds, and amphibious animals, Nature, to restore 

 the equilibrium among her creatures, and particularly to prevent the prepon- 

 derance of some sorts of insects, makes use chiefly of insects themselves, 

 namely, those which feed upon others, and which by degrees obtain a supe- 

 riority over those that are hurtful to us. 



349. Thus many sorts of beetles, particularly of the family of ground- 

 beetles (Carabidae), destroy a multitude of the pupae of moths lying in the 

 earth. Many flies, allied to our house-fly, but much larger, lay their eggs 

 in living caterpillars and destroy them. But the most useful are the /chneu- 

 monidse. The females of this numerous family, 1300 species of which Pro- 

 fessor Gravenhorst has described in Europe alone, lay their eggs entirely hi 

 the bodies of other insects. 



350. The manner in which these IchneumonidcB accomplish their work of 

 destruction is highly curious and interesting. All the species are furnished 

 at the end of the body with an ovipositor, composed of several bristles 

 attached together, with which they pierce the larvae of other insects, and 

 introduce their eggs into the flesh of the wounded animals. In some this 

 sting is longer than the whole body, sometimes more than an inch long, 

 namely, in those species which seek the objects of their persecution in the 

 interior of trees or wood that has been much and deeply perforated by the 

 insects which reside within. They perceive, either by their sense of smell 

 or by their antennae, that their prey is at hand, and introduce their eggs, 

 not without difficulty, into the bodies of the larvae living in the wood. Some 

 attack caterpillars feeding openly on plants, others perforate the various 

 excrescences, or gall-nuts, which also contain larvae : there are even many 

 species, scarcely visible to the naked eye, which lay their eggs in the eggs of 

 other insects, such as butterflies, and thus anticipate their destruction. The 

 eggs are hatched within the body of the living insect, and the young para- 

 sites, in the most literal sense, fatten on the entrails of their prey. At last 

 the wounded caterpillar sinks, the enemies escape through the skin and 

 become pupae ; or the caterpillar, notwithstanding its internal parasites, 

 enters the pupa state, but instead of a butterfly, one or more /chneumonidae 

 appear. To these wonderful animals we often owe the preservation of our 

 orchards, woods, and grain. 



351. Besides the above-mentioned Jchneumonidae, ants, field or tree bugs, 

 and many sorts of spiders, contribute greatly to the extirpation of various 

 insects. 



Subsect. 7. Means devised by Art for arresting the Progress of Insects in Gardens, 

 or of destroying them there. 



352. Insects may be destroyed in all their different stages ; in some, how- 

 ever, with greater ease than in others. Some can only be taken or killed 

 when in the perfect state, from the difficulty of discovering their eggs, or 

 from their small size, or from the short period which elapses between the 

 hatching of the insect and its maturity ; for example, the aphides. Others 

 can only be destroyed in the perfect state, with great difficulty ; such as the 

 different butterflies. A great number of the insects which infest British 

 gardens are only to be destroyed in the larva state ; while some, such as the 

 gooseberry-moths, may be destroyed in every stage. We shall briefly 

 indicate the different practices which may be had recourse to in different 

 stages, for deterring or destroying insects, by the gardener ; leaving particular 



