THE CANADIAN ENTOMOLOGIST. 88 



an ichneumon depicted with her ovipositor fully inserted in the tree and 

 with the side-pieces or sheaths sticking straight out behind her. Such an 

 attitude is altogether unnatural, and I am convinced that in that position 

 she would be powerless to extract the ovipositor. 



Selecting a suitable tree, if we find no ichneumons at work, we may 

 shortly see one flying strongly and noisily through the sunny woods and 

 settling upon the bark where perforations mark the exits of previous occu- 

 pants. Here she runs around until she finds a promising spot, as, for 

 instance, the hole made by a Tremex in depositing her egg. Placing 

 herself so that the tip of her abdomen will be above the orifice to be 

 probed, she makes herself as tall as possible, and, by elevating her abdo- 

 men and curving 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 capable 

 of being so dilated as to form a cavity in the posterior part of the abdo- 

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

 ovipositor, which thus becomes perpendicular under the insect, where it is 

 guided and supported by the sheaths which bend up in loops over her 

 back. By vigorous muscular contractions of the sac, the delicate ovi- 

 positor is slowly forced down the larva's burrow, often to its full extent. 

 If a larva be reached an egg is deposited in it, and the ovipositor is 

 slowly withdrawn in a similar manner. This, however, the insect is 

 frequently unable to accomplish, and remains struggling until some bird or 

 tree-toad snaps her up, or she perishes from exhaustion. 



I have seen a large R. atrata with her ovipositor (five and one-quarter 



inches long) inserted four and one-half inches into a beech, so firmly that 



it was only by careful and vigorous pulling that I extracted it uninjured. 



The insects are to be found during the latter part of the summer ; R. 



Iwiator, as already mentioned, being much the more abundant. 



On the last day of June, 1879, while collecting in a grove just beyond 

 Rideau Hall, I stopped to examine a dead tree for bark and fungi beetles, 

 and was bottling a fine Penthe pimelia, when the rustling of insect wings 

 above me attracted my attention. Looking up I saw several specimens 

 of Imiator flying about the trunk, and a circuit of the tree with closer 

 inspection showed many others walking about on the bark or in various 



