38 The Ohio Naturalist. [Vol. VII, No. 2^ 



NOTE ON HABITS OF SENOTAINIA RUBRIVENTRIS MACQ.* 



Herbert Osborn. 



This species of tachinid has been observed on several different 

 occasions at Cedar Point, and its habits are of such interest that 

 the record of some of these observations may be in place. In 

 the vicinity of the laboratory certain pompilid wasps are quite 

 common and may very frequently be seen dragging spiders with 

 which to provision their nests. On several occasions during 

 the summers of 1905 and 1906, I have observed these tachinid 

 flies following the wasp as it drags its burden along the sand. 

 The flies may vary in number from two to as many as nine, the 

 highest number noticed, and in following the wasps hover at a 

 very constant distance, about six or seven inches, progressing 

 and halting almost mechanically with the movement of the 

 spider. If the spider is dropped, the flies remain stationary, 

 hovering an inch or tw^o above the surface of the sand or, if the 

 spider is left for some minutes, they may rest upon the sand, but 

 always with the head directed toward the spider, and apparently 

 with the attention concentrated fixedly upon it. So intent are they 

 upon this object that they may be pushed about with a stick or 

 otherwise interfered with, with scarcely any diversion from their 

 intentness. Immediately upon the return of the wasp and move- 

 ment of the spider ,they are on the wing and maintaining the 

 constant distance noted. The wasp appears to pay but little 

 attention to them, although if approached too closely, it may 

 show some slight indication of annoyance and the flies appear to 

 be on the alert for any oft'ensive action on the part of the wasp. 



On one occasion I had the opportunity to see the actual en- 

 trance of the flies into the burrow. The flies hovered at about 

 the usual distance froin the spider while it was resting at the 

 mouth of the burrow, but appeared unusually excited, making 

 quick movements sidewise in maintaining attention upon the 

 spider and when finally the spider was dragged into the burrow 

 a very quick movement was made and some of the flies were seen 

 to actually pass down in the burrow but apparently only one 

 or two succeeded in entering and remaining; perhaps the one 

 first getting opportunity to enter being recognized as the rightful 

 inhabitant. Clearly the entrance of the burrow was for the pur- 

 pose of depositing eggs and we cannot doubt that the species 

 is parasitic within the nest of this pompilid. A related species, 

 Senotainia trilineata, is recorded as being reared from the nest 

 of Sphecius speciosa. The species was kindly determined for me 

 by Prof. J. S. Hine. 



♦Read at the meeting of the Ohio Sla'.e Acud. of Science. 



