THE BLUE SAND-WASP. 363 



adopt in performing this important business. They 

 first moisten the clay, then temper it into a little lump 

 of the size and shape of a swan-shot, and apply it 

 to the walls of their nest. They commence their 

 operations at the upper part, and work downwards, 

 till the cell is long enough to contain the chrysalis. 

 After having spread out this little lump in a pro- 

 per manner, they return tor fresh materials. 

 They cease their humming noise the moment they 

 depart from their cell, but always commence it im- 

 mediately on putting together the materials thev 

 have been out for. When a cell is finished, they are 

 always very careful to render it perfectly smooth on 

 the inside. 



The insects that this fly secures for its young are 

 principally spiders, which will in some measure ac- 

 count for its generally forming its cell under roofs of 

 buildings, and other places where spiders are usually 

 found. It does not kill them, but only in some 

 manner so disables them that they cannot escape; by 

 which means they are preserved alive and uncor- 

 rupted till the young larva is produced, which is not 

 long after the egg is deposited. They sometimes 

 seize and fly off with spiders that are equal in size 

 to themselves ; and when one of them proves too 

 weighty to be carried off, if it is not at a great distance, 

 the insect drags it to her nest. Mr. Catesby once 

 saw an exceedingly large spider dragged up a wall 

 by one of these Hies to its nest ; and both of them 

 being caught and weighed, it was found that the 

 spider was eight times the weight of the fly. 



By the time the larva has devoured all its provi- 



