INTRODUCTION 



It has been aptly said that, while birds are the Sauls who slay their thou- 

 sands, Ichneumons are the Davids who slay their tens of thousands. Were 

 it not for the check the latter so effectually exercise over the ever increasing 

 multiplicity of other insects, it is probable we should be able to procure no 

 surface vegetables for our tables, no corn for our bread, no flowers for our 

 vases, and, above all, that the landscape would become devoid of the lovely 

 herbage, leaves, grasses, plants and even trees, presenting a brown and 

 barren waste of sterility. All moths and butterflies lay some hundreds of 

 eggs apiece, and if each of these attained maturity to go and lay another 

 hundred, their numbers would so quickly increase that the plants upon 

 which they subsist would speedily be extirpated. What has at various 

 times been noted in this respect ^ has caused utter ruin. A single instance 

 may be cited of the prodigies possible to insects which have been imported 

 into strange lands without the Ichneumons essential to the preservation of 

 their normal numbers. Mr. Bignell has concisely set forth the damage com- 

 mitted by the Gipsy Moth in North America. This scourge was imported 

 by a French naturalist, who allowed a few specimens to escape, in 1869 ; 

 twenty years later the heel of the invader was felt throughout two hundred 

 and twenty square miles of country ; the larvae completely defoliated the 

 trees ; hundreds of men are regularly employed in their destruction and 

 have, since 1890, inspected and re-inspected over forty-two million trees, 

 and have killed about two-and-a-half billion larvae. Twenty thousand 

 pounds /^r afinuvi has been necessary for the work. This expenditure has 

 lately increased and the pest is only reduced to seventy-five miles of forest. 

 Now, if that French naturalist had only turned loose an antidote in the 

 form of a few Ichneumons after the escaped moths, we should have heard 

 no more about them, for they would have been restricted to respectable 

 propagation. 



So vast a mass of literature has been compiled respecting the parasitism 

 of the Ichneumonidae that it is totally impossible to do more here than 

 give some meagre outline of it, and to take, as relating to the present 

 volume, the lines pursued in common by the majority of the Ichneu- 

 moninae. The eggs of this family are invariably deposited in or upon 

 the larvae of insects and among the eggs of, or upon mature, spiders.'^ 

 Lepidoptera exclusively constitute the victims of the Ichneumoninae, and 



1 Cf. Curtis, Farm Insects, p. 78 ; Miss Ormerod's Reports, &c. 



'■2 I know of no aiulientic instance of their deposition in the pupa ; and Westwood has shown 

 (Introd. ii., 144) observations upon the presence of pliytophagous larvae in tliis family to be fallacious, 

 as also we are led to consider those set forth in Ent. Kec, 1900, p. 293. 



