60 MEANS FOR ARRESTING THE PROGRESS OF 



restore the equilibrium among her creatures, and particularly to pre- 

 vent the preponderance of some sorts of insects, makes use chiefly of 

 insects themselves, namely those which feed upon others, and which 

 by degrees obtain a superiority over those that are hurtful to us. 



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 Ichneumonidae. The females of this numerous family, 

 1300 species of which Professor Gravenhorst has assigned to Europe 

 alone, lay their eggs entirely in the bodies of other insects. 



The manner in which these Ichneumonidae accomplish their work of 

 destruction is highly curious and interesting. All the species are fur- 

 nished 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 

 requirements 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 

 Ichneumonidae appear. To these wonderful animals we often owe the 

 preservation of our orchards, woods, and grain. 



Besides the above-mentioned Ichneumonidae, ants, field or tree bugs, 

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

 various insects. 



Means devised by Art for Arresting the Progress of Insects in 

 Gardens, or of Destroying them there. 



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 



