Wasps, Bees, and Ants 483 



attack on certain of the solid tissues, as muscles, fat-body, etc. Such attacks 

 necessarily avoid the vital organs or the host would be killed long before 

 the parasitic larva is ready to pupate. With regard to the breathing it has 

 been variously suggested that the larva applies itself to air-tubes (tracheae) 

 in the host-body in such a way as to effect an exchange of gases ; that it needs 

 no more oxygen than it obtains in the body fluid of the host; that its rela- 

 tion to the host is analogous to that of foetus to mother among viviparous 

 animals. Seurat's observations seem to indicate (for certain species at 

 least) that solid food as well as blood-lymph is taken in; that respiration 

 is effected through the skin by osmosis, that excretion from the intestine 

 does not occur until after the pupal cocoon is formed, and that moulting 

 actually occurs. 



The host of species and the difficulties attending their determination, 

 even (for amateurs) as regards their family classification, let alone their 

 generic and specific identification, have led me to avoid any reference to the 

 systematic study of these parasites. Certain particular species, especially 

 among the larger forms, are of course more or less re- 

 cognizable and familiar to observers. Among the larger 

 species, most of which belong to the superfamily 

 Ichneumonoidea, those of the genera Pimpla (Fig. 678) 

 and Ophion (Fig. 679) are especially familiar. P. con- 

 quisitor (Fig. 680) is the commonest parasite of the tent- 

 caterpillars (Clisiocampa), is also the chief one of the de- 

 structive cotton-worm, Aletia argillacea, of the south and 

 has been bred from half a dozen other species of moths. 

 It lays its eggs not on the larva? of the tent-caterpillar 

 moth, but on the pupae (and perhaps on the cater- FIG. 680. Pimpla 

 pillars after spinning and just before pupating) inside ^fft^JfS 

 the silken cocoon (Fig. 680). P. inquisitor, a common American tent-cater- 



parasite of the tussock-caterpillars, is an ichneumon- P 1 . 11 . ar m th - ( Afte ^ 

 r ... . . Fiske ; about natural 



fly whose life-history is given in much detail by Howard size.) 



in the Insect Book. The Ophions are light brown or 

 golden in color, with abdomen much compressed laterally. A common 

 species parasitizes the giant larvae of the polyphemus moth ; but huge as 

 this caterpillar is, only one egg is laid on it by the Ophion. 



The wonderful Thalessa, with its flexible ovipositor six inches long, with 

 which it drills a hole deep into a tree-trunk until it reaches a tunnel of the 

 wood-boring larva of Tremex, has already been referred to (see p. 467). 

 Comstock describes Thalessa as follows: "Its body is 2\ inches long and it 

 measures nearly 10 inches from tip of antenna to tip of the ovipositor. 

 When a female finds a tree infested by the Tremex she selects a place which 

 she judges is opposite a Tremex-bunow, and, elevating her long ovipositor 



