SOLITARY INSECTS. 181 



otherwise it could not exist. Reaumur discovered that air 

 actually penetrated through this seemingly compact mason- 

 work. 



As soon as the first cell is completed, the mason-bee lays 

 the foundation of another. In the same nest she often con- 

 structs seven or eight cells, and sometimes only three or four. 

 She places them near each other, but not in any regular order. 

 This industrious animal, after all her cells are constructed, 

 filled with provisions, and sealed, covers the whole with an 

 envelope of the same mortar, which, wher^dry, is as hard as 

 stone. The nest now is commonly of aiTioblong or roundish 

 figure, and the external cover is composed of coarser sand 

 than that of the cells. As the nests are almost as durable as 

 the wall on which they are placed, they are often, in the fol- 

 lowing season, occupied and repaired by a stranger bee. 

 Though inclosed with two hard walls, when the fly emerges 

 from the chrysalis state, it first gnaws with its teeth a passage 

 through the wall that sealed up the mouth of its cell ; after- 

 wards, with the same instruments, it pierces the still stronger 

 and more compact cover which invests the whole nest ; at last 

 it escapes into the open air, and, if a female, in a short time, 

 constructs a nest of the same kind with that which the mother 

 had made. To all these facts, Du Hamel, Reaumur, and 

 many other naturalists of credit and reputation, have been re- 

 peatedly eye-witnesses. 



From the hardness of the materials with which the mason- 

 bee constructs her nest, from the industry and dexterity she 

 employs to protect her progeny from enemies of every kind, 

 one would naturally imagine that the young worms were in 

 perfect safety, and that their/ castle was impregnable. But 

 notwithstanding all these favorable precautions, the young of 

 the mason-bee are often devoured by the instinctive dexterity 

 of certain species of four-winged insects, distinguished by the 

 name of ichneumon-flies. These flies, when the mason-bee 

 has nearly completed a cell, and filled it with provisions, de- 

 posit their own eggs in her cell. After the eggs of the ich- 

 neumon-flies are hatched, their worms devour not only the 

 provisions laid up by the mason-bee, but even her progeny 

 whom she had labored so hard, and with so much art and in- 

 genuity, to protect. But the mason-bee has an enemy still 

 more formidable. A certain fly employs the same stratagem 

 of insinuating an egg into one of her cells before it is com- 

 pleted. From this egg proceeds a strong and rapacious worm, 

 armed with prodigious fangs. The devastations of this worm 

 16 



