374 



used this character to distinguish the pupae of Asilidae from those of 

 Bombyliidae, the latter having alternating stout thorns and long 

 slender hairs in the transverse armature of the abdominal segments, 

 but owing to the occurrence in Leptogaster fiavipes of an armature 

 that differs almost as decidedly from that of other Asilidae as it 

 does from Bombyliidae I have had to re-draft the statement of dis- 

 tinctions. In all the Bombyliidae known to me there are 2 closely ap- 

 proximated thorns on the lower central portion of the face, which are 

 in some species fused almost to their apices; these thorns I have not 

 found present in any species of Asilidae, not excepting Leptogaster. 

 It is not improbable that further revision will be necessary as the 

 pupae of more genera are obtained. 



Imago. — The synoptic key to imagines of Brachycera presents a 

 summary of the characters for the recognition of the imagines. The 

 generic key in Williston's "Manual of North American Diptera" is 

 sufficient for the identification of the genera. 



HABITS OF LARVAE 



All of the larvae of this family that I have found, are predaceous, 

 feeding upon other insect larvae, either in decaying wood or in the 

 ground, and may thus be considered generally as beneficial. Several 

 species, such as Promachus fitchii, P. vertcbratus, Deromyia discolor, 

 D. winthemi, ProctacantJuts milbcrti, Brax maculatus, and E. 

 aestnans are instrumental in reducing the numbers of white-grubs in 

 cultivated ground. Asilus notatus and Leptogaster fiavipes I have 

 found only in or near woods, and especially in or under decaying 

 wood, and it is very probable that they confine themselves to attacks 

 upon species that are found in such situations — Tenebrionidae and 

 Cerambycidae particularly. 



The transformation to the pupal stage is preceded by four or five 

 days in a semi-quiescent condition, during which the gradual develop- 

 ment of the imaginal parts may be clearly seen through the transpar- 

 ent skin of the larva. The pupa is capable of making its way through 

 the ground either backward or forward, and prior to the exclusion 

 of the imago makes its way to the surface, where the exuvium is left 

 projecting half-way out of the ground after the imago has flown 

 away. 



HABITS OF IMAGINES 



Like the larvae, the imagines are predaceous as a general rule, but 

 very often some species may be taken on flowers, where they undoubt- 

 edly partake of the nectar. Some of the genera I have taken only on 



