91 
asilid larvae differ noticeably from tabanid larvae in their feeding habits, 
the latter using their mandibles to tear the skin of the host and being 
exceedingly quick in their operations, while the asilids are slower in 
their movements and pierce their host by a puncture rather than by a 
cut or tear. The pupal form, and especially the brown chitinized spines 
and the stigmal spots, can be seen beneath the larval skin several hours 
Fic. 21. Promachus vertebratus Say, pupa. 
before pupation actually takes place. As the larval skin splits the pupa 
rapidly emerges, requiring less than a minute and a half to complete its 
exit. The head and body segments of the pupa are well armed with 
rigid spines (Fig. 21) which it uses to advantage in pushing itself to the 
surface of the soil just before the emergence of the imago. Pupation 
occurs, according to our records, from May 26 to July 18, and the adults 
issue from June 15 to August 18, the pupal period varying from 19 days, 
in rare instances, to 39 days, with an average from 55 examples of 32.++ 
Fic. 22. Promachus vertebratus Say, male. 
days. Of the 59 adults reared and recorded as to sex, 29 were males 
and 30 females. The fly is very characteristically shown in Figure 22 
and in Plate VII, Figure 26. The female lays its whitish, elliptical eggs 
in fall in cracks in the soil or in little earthen cavities which the female 
makes, usually several eggs being laid together. The larvae upon 
hatching search the soil for food, probably feeding at first on small 
