INSECT-ARCHITECTURE. 185 



feet, and when the sand accumulated so as to be in its way 

 it would retreat backwards and push the dirt still farther 

 back from the mouth of its cell with its hind legs. In this 

 way, working literally with tooth and nail, it dug a shaft 

 five or six inches deep, and then flew away after grass- 

 hoppers to store it, finally filling the mouth so that no dis- 

 tinct traces of its work would remain. 



A decided step upward is the home of 

 the mud-dauber. This wasp moistens 

 the dirt with its saliva, forming pellets 

 of mud, which it plasters on walls or 

 rafters, storing the cell with spiders, 

 etc. In our common yellow-legged mud- 

 dauber (Pelopceus flavipes) the cells are 

 built of long pellets of mud placed in 

 two rows, and diverging from the mid- FIG 234 _ An Afrjcan 



cQ0. mud-dauber. 



The wood -wasps excavate their burrows in the hollow 

 stems of pithy plants, such as the elder, syringa, raspberry, 

 or blackberry, the idea seeming to be to save as much labor 

 as possible; some species going so far, or rather doing so 

 little, as to refit old nail-holes for their nesting purposes. 



Coming to the true solitary wasps, we find species of 

 very different nest-building habits. While one kind of 

 Odynerus builds separate cells of mud, placing them in 

 oak-galls or in deserted nests of the tent-caterpillar, another 

 builds several cells together under a common covering of 

 sandy mud fastened to a stack of grass. More of an archi- 

 tectural effort is seen in the flask-shaped cells of mad which 

 Eumenes fraterna, builds, attaching several of them in a 

 row to a branch, filling the interiors with little caterpillars. 



Of a more advanced order is the nest of Icaria, which 

 shows that each cell is built independently in regular hex- 

 agons; sometimes the cells are arranged in two or three 

 rows; while in the nest of our Pollutes annularis, often to 

 be found attached to bushes, the cells are crowded together 

 in one plane or story. But in a delicate nest of a South 



