A NATURAL CEMENT 



made of mud or dust are not very durable structures even 

 when strengthened with a cement of adhesive saliva, and it 

 has occurred to them to introduce rubble as an additional 

 material. In spite of the circumstance that it is very diffi- 

 cult for them to fly about burdened with pieces of grit, they 

 have succeeded very well in their enterprise, and the sub- 

 stance of their buildings may be compared to that mixture 

 of cement and gravel which is known as ' rough-cast.' 



A very good example of this is found in the Mason 

 Bees called Chalicodoma, whose cement-built houses are some- 

 times so firm that it is necessary to use iron instruments if 

 you want to break into them. These nests are placed on 

 rocks, or more usually on old walls, those which face south 

 being preferred for the purpose, and they have the appear- 

 ance of big splashes of mud made by the wheels of passing 

 vehicles, or thrown up from the horses' feet. The builders 

 are so particular about the solidity of their dwellings that 

 they carefully avoid attaching them to plastered walls or to 

 mortar between the stones, but build them on the stone 

 itself; and, as if not content with this precaution, they 

 nearly always choose in addition the place in which they can 

 be most securely .fixed, preferring especially the angles formed 

 by copings, plinths, window-sills, and so on. 



As M. Fabre has told us, the mason bee's building material 

 consists of chalky clay mixed with a little sand and hardened 

 with the insect's own saliva. Damp soil, which would not 

 only be easier to work but would also require less saliva for 

 making the mortar, is passed by disdainfully ; a Chalicodoma 

 rejects moist earth for building as certainly as a bricklayer 

 would reject old plaster or 'spent' lime. Such materials, 

 sodden with water, would not take a good hold. What the 

 insect wants is perfectly dry dust which will readily soak up 

 the saliva which is poured upon it, and form, with the 



