58 



TROPICUS 



Garrey observed that when the lower halves of the 

 eyes of the robber fly are blackened the position of the 

 legs of the two sides is symmetrical, but the anterior and 

 middle pairs of legs are extended forward to the maximal 

 extent, producing a striking posture in which the anterior 

 end of the robber fly is pushed up and back from the sur- 

 face of the table. The body is in opisthotonus with the 

 abdomen concave on the dorsal side, while the head is 

 tilted far up and back (Fig. 21). 



Fig. 22.— Position of robber fly when upper halves of both eyes are blackened. Head down, 



body convex above. (After Garrey.) 



When walking these robber flies gave the impression of trying to 

 climb up into the air. The wings are frequently somewhat spread and 

 the animal may push itself up and back until poised vertically on the 

 tips of the wings and abdomen. The tendency to fly is very pronounced 

 in this condition and upon the slightest disturbance the fly soars upward 

 and backward, striking the top of a confining glass dish or completing 

 a circle by " looping the loop " backward. If it falls upon its back 

 it rights itself by turning a backward somersault. Unequal blackening 

 of the lower parts of the two eyes results in a combination of the effects 

 just described, with those described for blackening one eye, for the 

 animal also performs circus motions. 



With the upper halves of the eyes blackened the attitude is the 

 reverse of that described in the preceding section (Fig. 22). The an- 

 terior and middle pairs of legs are flexed. The anterior and posterior 



