Report of the State Entomologist. 157 



Its Different Names. 

 This curious insect, one of the largest of our Ichneumons, origi- 

 nally described by Fabricius as Ichneumon lunator, is figured and 

 briefly referred to by Dr. Harris, in his Insects Injurious to Vegetation, 

 as Pimpla lunator. Later writers have referred it to the genus 

 Rhyssa, but Mr. Cresson, in his recent arrangement of the group, 

 has separated it from that genus and placed it in Thalessa, of Holm- 

 gren, together with four other United States species, one of which is 

 the common "black long-sting," or T. atrata. The specific name of 

 lunator is drawn from the yellow crescents (shown angular in the 

 figure) which mark the sides of the abdomen, one upon each 



segment. 



Description. 



The insect has been described by Mr. Harrington [loc. cit.) as vary- 

 ing much in size, the larger specimens being fully twice as large as 

 the smallest ones. The body varies in length from three-fourths of 

 an inch to one inch and a half, and bears at its posterior extremity an 

 ovipositor projecting from one and one-half to three and three- 

 fourths inches. 



The head of the female is yellow, with a dark band on its summit, 

 in which are inserted the three ocelli between the eyes, parallel to 

 which and posterior to it runs another dark line which almost encir- 

 cles the head; lines also run from the base of the antennae to the 

 mandibles. The slender autennge are dark brown, many jointed, and 

 about an inch long. The thorax and abdomen are dark brown, orna- 

 mented with lines and bands of yellow, which is also the color of the 

 legs. The abdomen is gradually flattened laterally toward its extremity, 

 where it is broadly dilated. The front wings expand from one and 

 one-quarter to two and one-half inches, and have a quadrangular 

 dark patch on the anterior border, and a brown patch at their tip. 

 The black ovipositor, given out from the fifth segment beneath, varies 

 in different sized individuals, from one and one-half to three and 

 three-fourths inches in length, and is flattened on its sides. Its two 

 guides of nearl}^ the same length and proceeding from the extremity 

 of the abdomen are broader, and are channeled for the reception of 

 the ovipositor and for holding it when serving as supports. 



Is not Injurious, but Beneficial. 

 Contrary to the belief of many of those who have seen the opera- 

 tions of this insect and who entertain the opinion that all of the 

 boring insects are harmful to the vegetation that they attack, this 

 one is not only not injurious, but it renders excellent service in the 

 destruction of a noted pest of several of our shade trees. It is from 



