H Y MEN OP TERA. 



623 



the species are mostly of considerable size, and here belong the 

 larger of the parasitic Hymenoptera. In this family the wings 

 are furnished with several closed cells ; the fore wings have 

 a stigma ; and cells V\ and ist V a are separate (Fig. 748). 



The largest members of the family belong to the genus 

 Thalessa. These are remarkable-looking insects, with long, 

 slender bodies and three long hairs at the end of the body. 

 Two of these hairs form a sheath for the third, which is the 

 ovipositor. This ovipositor, although apparently merely a 

 thread, is really composed of three pieces placed parallel, 

 one above and two below, and securely locked together. 

 Near the end of them are ridges like those on a file, and 

 between them is a passage through which the egg is forced 

 when it is laid. 



Thalessa lunator (Tha-les'sa lu-na'tor) is one of the 

 larger of our Ichneumon-flies. Its body is two and one 

 half inches long, and it measures nearly ten inches from 

 the tip of the antennae to the tip of the ovipositor. It 

 is a parasite of the wood-boring larva of the Pigeon Horn- 

 tail. When a female 

 finds a tree infested by 

 this insect she selects a 

 place which she judges is 

 opposite a Tremex-bur- 

 row, and, elevating her 

 long ovipositor in a loop 

 over her back, with its 

 tip on the bark of the 

 tree (Fig. 749), she 

 makes a derrick out of 

 her body, and proceeds 

 with great skill and pre- 

 cision to drill a hole into 

 the tree. When the 



Tremex-burrow is FIG. 749. r//j 



reached she deposits an egg in it. The larva that hatches 



