r iv SOCIAL HOMES 147 



by small oval apertures. In some cases the walls are 

 reduced each into two pillars, rendering the apertures 

 larger and rounder. When the work is still more 

 advanced the holes become square, and the pillars 

 originally arched at both ends are hewn into straight 

 regular columns, giving a palatial aspect to the excava- 

 tion. Further progress transforms these partitions 

 into light cylindrical columns possessed of a base and 

 capital which are arranged in colonnades, leaving a 

 free communication throughout the whole extent. The 

 rooms on or about the same plane when complete 

 necessarily form a storey, but since they are hollowed 

 out separately, though on similar plan, and the sides 

 are chiselled away as time goes on, saving material 

 sufficient to sustain the ceilings, the flooring cannot 

 possibly be very level. This seems a boon rather 

 than a disadvantage, for the irregularities appear 

 to answer as cradles for the larvae. In roots 

 sometimes, as in Australia, the nests look like 

 charming net-work. The material carved be- 

 comes black, as if smoked, due to exposure of 

 the wood to the atmosphere, to some emanation 

 from the ants, or to the action of formic acid (see 

 Fig. 22). 



Wood-carving ants also infest the beams of houses, 

 and imperil their safety. 



Two other tribes of Carpenters, F. cethiops and F. 

 flava> the yellow ant, have the ingenuity to utilise 

 the saw-dust that they chisel away. The former 

 applies it to stopping up chinks and to the 

 building of walls ; the latter, more skilled and in- 

 ventive, composes entire stories of it stiffened and 



L 2 



