HOW CAN AN " ACULEATE BE RECOGNIZED ? 93 



They are known by a combination of many, 

 and these are frequently small structural details 

 which do not appeal to the field observer ; in 

 fact, which are unappreciable except under 

 magnification. One of the chief difficulties 

 experienced by an observer who is not versed in 

 classification is to avoid being deceived by various 

 flies, which in many cases greatly resemble bees, 

 and especially wasps or the wasp -like fossors. 

 They may mostly be known by their flight, and, 

 when they settle, by their behaviour. A fly is 

 more sudden in its movements those wasp -like 

 flies, for instance, which poise themselves in the 

 air and appear quite stationary but dart of! in a 

 second when approached, betray themselves at 

 once by their alertness. Anthophora and Saropoda 

 poise in the air and dart somewhat after the same 

 fashion, but they never remain poised for long, and 

 do not get away from their position so rapidly. 

 Also, a fly when it settles remains quiet, whereas 

 an aculeate if in a flower sets to work collecting 

 pollen, or if basking in the sun on a leaf rarely 

 rests for many seconds without moving in some 

 way. On a flower, if an insect is seen quietly 

 sitting with its head away from the centre of the 



