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Method of Oviposition of Tachina. 

 By Archibald C. Weeks. 



An opportunity to observe a female Tachina in the act of oviposit- 

 ing is, I presume, of comparitively rare occurrence and as such an oppor- 

 tunity was vouchsafed me, I may, perhaps, without trenching upon what 

 has been previously noted, describe the process. 



On September 3d of this year, noticing a small Hickory almost en- 

 tirely denuded of foliage by a brood of Datana larvae, I stopped to watch 

 the industrious feeding of a cluster of them. 



Upon one of the leaves near the heads of the larvae was a female 

 Tachina standing unusually erect and regarding the larva; very intently. 

 Divining her purpose I remained quiet. After the lapse of several 

 minutes she cautiously approached the head of the nearest and there- 

 after constantly adjusted her position so as to face the larva as it 

 moved in feeding at a distance of rather less than a quarter of an inch. 

 Seizing a moment when the head of the larva was likely to remain statio- 

 nary the fly stealthily and rapidly bent her abdomen downward and ex- 

 tended from the last segment what proved to be an ovipositor. This 

 passed forward beneath her body and between the legs until it projected 

 beyond and nearly on a level with the head of the. fly and came in con- 

 tact with the eye of the larva upon which an egg was deposited in addi- 

 tion to five already there. So gently was this done, that the larva did not 

 at first appear to be disturbed, but presently the adhesion of a foreign 

 substance seemed to annoy it and it scraped its eyes against the bitter 

 edge of the leaf in a vain effort to rub off the barnacledike ova. The fly 

 then proceeded to several other larvae, which had been previously simi- 

 larly stung, and repeated the process, always ovipositing on or between 

 eyes at which place at least a dozen had been attacked, and nowhere else. 

 The presence of other ova did not deter the fly from adding to the num- 

 ber. The ovipositor was viscous of a pale yellow, tapering, and elastic 

 to such a degree that the entire abdomen could hardly have contained it 

 as expanded. 



It was interesting to note that the fly carefully avoided allowing her 

 ovipositor to come in contact with the fine long hairs of the larvae which 

 hung over the eyes, withdrawing it instantly upon their slightest move- 

 ment. Judging from the fact that no ova appeared to have been deposited 

 on the segments it is safe to assume that even the sparse hairs of the Da- 

 tana larvae constitute a barrier which the moist and highly sensitive ovi- 

 positor of the Tachina can not overcome. 



We have here an additional proof that even the slightest hair or spine 

 development adds to the safety of its possessor. 



