18 THE EARLY STAGES OF TABANID.E 



The newly hatched larvae drop into the water or onto the ground, 

 according to the egg-laying habits of the species, and little is known 

 about them. The young larvae resemble the full grown in appearance, 

 but are generally more transparent, showing the internal organs, a 

 pair of black eye-spots, and Graber's organ in its primary condition, 

 which is later described. The chordotonal organs have been described 

 in young tabanid larvae. The nervous system is clearly visible. The 

 young larvae may be fed on tiny crustaceans, crushed insect larvae, etc., 

 but are not always successfully reared. 



Of the young larvae some have strongly developed tracheal trunks 

 which enable them to float, while others sink to the bottom. 



All tabanid larvae are highly predacious, feeding on other insect 

 larvae, earthworms, and probably all animals they can get hold of, 

 not sparing their own kind. Wahlberg found them, according to 

 Brauer, semiparasitic in lepidopterous (noctuid) larvae. Perris 

 reports that he has found them under stones feeding on larvae of 

 Rhizotrogus and on Melolontha (imago?). According to Brauer, 

 young larvae burrow into other larvae (of beetles) and leave these 

 only when they completely fill the skin of the host. Brauer once 

 obtained the larva of Hamatopota from the larva of Helops lanipes, 

 from which, as it seemed to be molting, the tabanid larva made its 

 way. Walsh states that they feed on snails; Hine and others fed them 

 on earthworms. Young larvs can be fed on small crustaceans 

 (King). It is not known what food they take in nature, and also 

 whether they can subsist on vegetable food. Del Guercio's statements 

 on this point are probably erroneous. Mitzmain and others have 

 observed their cannabalistic tendency, at least in captivity. As Pat- 

 ton and Cragg have stated, the larvae of the large species and of 

 the nearly allied full grown stages of the smaller species feed almost 

 exclusively on earthworms whose body juices they suck out; this 

 explains why gregarine cysts {Monocystis) are not uncommonly found 

 in the alimentary tract of the imago. Malloch says that the food of 

 the species occurring in rivers is mostly tipulid and other larvae which 

 burrow in the soft banks of the rivers or occur in the river bottom or 

 in drift. 



Structure of the Mature Larva. — All the known larvae of tabanids, 

 with the exception of the somewhat aberrant Gonoips, are elongate, 



