158 Forty-first Report on the State Museum. 



its large size and peculiar appearance, a distinguished member of 

 the large family of Ichneumonidce, the province of whose members it 

 is to prey upon other insects, often so effectively as to rid us of some 

 of our greatest insect scourges, when all human efforts to arrest their 

 multiplication and injuries have been of no avail. 



It Preys upon Tretnex columba. 

 The trees in which T. lunator is often seen inserting its long ovi- 

 positor for the deposit of its eggs, 

 are largely infested by the grubs 

 of the pigeon Tremex, Tremex co- 

 lumba Linn., upon which the larva 

 of T. lunator, preys. The perfect 

 insect is a large, wasp-like creature, 

 as shown in Figure 16, with narrow, 

 semi - transparent, smoky - brown 

 wings, a reddish head and thorax, 

 and a long, cylindrical, black 

 body, marked with seven yellow 

 bands, most of which are inter- 

 FiG. 16.— The Pisreon Tremex — Teemex rupted on the middle. The body 

 coLUMBA,-female. ^^^^,^ beneath a black ovipositor of 



about an inch in length, projecting three-eighths of an inch beyond its 

 tip, held in place by two guides — the whole forming a stout, horn- 

 like instrument, whence we have the common name of " horn-tails " 

 for this insect and its associate Uroceridm. The Tremex larvse run 

 their large and destructive burrows in the trunks of the maple, beech, 

 elm, oak, sycamore, apple, pear, etc., not infrequently causing the 

 death of the tree when the attack has been long continued. 



How Thalessa Oviposits. 

 The operation of boring for oviposition has been described by Mr. 

 Harrington, as follows: 



Sitting upon the bark where ^perforations mark the exits of pre- 

 vious occupants, she runs arouiid until she finds a promising spot, as, 

 for instance, the hole made by a Tremex in depositing her eggs. 

 Placing herself so that the tip of the abdomen will be above the 

 orifice to be probed, she makes herself as tall as possible, and, by 

 elevatiug her abdomen and carrying under the ovipositor, succeeds 

 in inserting the tip of the latter in the hole. 



If the dorsal surface of the abdomen be examined, there will be 

 observed, between the sixth and seventh segments, a gap closed by a 

 whitish membrane. This marks an admirable contrivance to enable the 

 insect to use her seemingly unwieldy weapon, for the membrane is so 

 dilatable as to be capable of forming a cavity in the posterior part of the 

 abdomen, in which can be coiled a large portion (more than one-third) 



