284 INSECT ARTIZANS AND THEIR WORK 



masonry. The time required for this operation 

 depends upon the thickness of the masonry at the 

 spot selected. It may be accomplished in a quarter 

 of an hour ; it may take three hours ! Fabre has 

 watched this burglar at her work, and marked her 

 incision of the masonry and put the date against 

 it. On opening the nests later he has found that 

 she has invariably hit upon the right spot and has 

 penetrated to a cell. 



But although she has this marvellous sense, a sort 

 of second-sight, that enables her to see, as it were, 

 what lies on the other side of the masonry, it is 

 disappointing to find that in one respect her sense 

 is defective. It cannot tell her that in some of 

 the cells her intended prey has already perished 

 and its food-supply dried up or gone mouldy. Nor 

 does it protect her from making the mistake of 

 piercing a cell that has already been penetrated, 

 once, twice, or thrice, either by herself or another 

 of her kind. Perhaps it is a necessity of the case, 

 in order that some Chalicodoma grubs should 

 survive and come to the winged btate. For it 

 must be explained that if a Leucosfis egg hatches 

 and brings forth a grub, that grub sucks the right- 

 ful occupant of the cell and leaves only an empty 

 shrivelled skin. 



In those cases where several Leucosfis eggs have 

 been placed in one cell, it is the care of the first- 

 hatched grub to search for the other eggs and 

 destroy them, for a Chalicodoma grub only serves 

 for the nourishment of one Leucospis. 



