116 PROTECTION OF WOODLANDS. 



parasitic species, on account of the larger amount of natural 

 nourishment and the greater opportunities of reproduction thus 

 offered to them. 



(a) Predatory species of Insects include the well-known pre- 

 daceous land-beetles (Carabidte), of which in particular the tree- 

 climbing species Calosoma sycophanta and C. inquisitor are useful, 

 the sand-beetles (Cicindelidai), the dung-beetles (Staphylinidse), the 

 gold-beetles (Cleridte, vide Plate I. fig. 2), the leaf -beetles (Coccinel- 

 lidae), the wasps (Vespidw), and predatory flies (Asilidss). Ants 

 (Formicidx) also devour numerous caterpillars, and trees near 

 ant-hills usually remain exempt from attacks of the latter. The 

 mole-cricket (Gryllotalpa vulgaris) is also an enemy of all insects 

 living in the soil, although, on the other hand, it often does con- 

 siderable damage to the roots of plants (vide par. 91). 



(b) Parasitic species of Insects include certain genera of flies 

 (Tachininse group of the Mustidae), easily distinguishable from other 

 ordinary flies by the rough, brush-like hairs on the abdomen (vide 

 Plate I. fig. 3), and ichneumon-flies (Ichneumonidte, vide Plate I. 

 fig. 1), which rapidly increase whilst attacks of caterpillars are 

 assuming calamitous proportions. Owing to their importance and 

 general distribution, these latter deserve some little attention here. 



The Ichneumon-flies, belonging to the order of the Hymenop- 

 tern, comprise very numerous genera, 1 which vary greatly in size 

 By means of a long ovi-depositor the female lays her 

 sometimes only singly, sometimes often in very considerabl 

 numbers in the case of the smaller genera (290 larvae of Micro- 

 goster globatus have been found in a single caterpillar of the Pine 

 moth, Gastropacha pini), in the ova or larvae, less frequently in 

 the chrysalides or imagines, of other insects. The minute larvae, 

 that soon make their appearance, subsist on the vital fluids of the 

 host they occupy, and when fully grown, bore their way out to 

 the surface; there they enter and pass through the pupal sta^c in 

 small cocoons, with which the dying caterpillars are often com- 

 pletely covered. The generation of the Ichneumonidae is partly 

 simple, partly manifold, in which latter case, as also when the 

 number of hosts is large, they are exceedingly prolific, ;m<l 

 increase rapidly in numbers. The hosts perish under all circum- 

 stances, although sometimes the caterpillars attacked enter the 



1 Hess, op. ctt., vol. i. page 213, states that there are 5000 species, and that about 

 1000 of these are parasitic on injurious forest insects. Trans. 



