VIII, B, 3 Mitzmain: Biology of Tabanus stnatus Fabricus 205 



tight place or in capturing food when it retreats into a channel 

 previously made in the sand. , 



The larvae readily adapt themselves to a watery medium. 

 They can remain submerged for several minutes at a time 

 without apparent discomfort. When placed in deep water the 

 movements of the body are a general struggling without ap- 

 parent definite purpose. At any rate, there is little or no 

 progression, the body doubles like a bow, the head and tail 

 meeting, then straightens with a whipping action. In swim- 

 ming, the body is held along the surface of the water and the 

 siphon is extended toward the air in a manner very suggestive 

 of the larva of an anopheline mosquito. The principal move- 

 ment observed is that of simple telescoping of one segment into 

 another. When speed is required or an obstruction is to be 

 passed, there is a vigorous whipping movement of the siphon 

 laterally, toward and away from the head. This latter move- 

 ment is also noted when the insect is disturbed. 



When a young larva is placed in water containing entomos- 

 tracans or other minute animals, a barely perceptible churning 

 of the liquid occurs in the region of the mouth. This disturbance 

 is no doubt caused by the movements of minute tentacles which 

 assist in procuring food. These tentacles form the armature 

 of the stomal disk, consisting of a process arranged like a turn- 

 stile mounted on a pitted chitinous plate at the base of the 

 great hook or mandible. In the very young larva the stomal 

 disk appears as a chaplet of delicate chitinous rods. When a 

 larva is treated with strong caustic potash, the stomal disk 

 appears to be the only structure which resists its action, the 

 other chitinous structures, even the heavy pharyngeal apophyses, 

 are bleached. In common with the other chitinous portions of 

 the head capsule the stomal disk is shed at each of the three 

 ecdyses. 



GENERAL DEVELOPMENT OF THE LARVA 



The young larva shows in its form and behavior its adapti- 

 bility to an aquatic life. This is well illustrated when a larva 

 is turned adrift in an aquarium containing mosquito wrigglers. 

 The Tabanus has no difficulty in keeping afloat with them and 

 foraging at will upon the active culicid larvae. Tabanus larvae 

 have been observed capturing wrigglers, holding them by 

 their jaws under the water, and actually killing the culicid 

 through drowning. In one instance a Tabanus larva held its 

 victim, which was fully five times its size, suspended beneath 

 it in such a manner that the culicid was unable to project 



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