The Mason-Wasps 



nests, but sparsely inhabited it is true, on 

 the trunks of trees, in the seams of the 

 rough bark of oaks. Among those whose 

 support was a living plant, I will mention 

 two that stand out above all the others. 

 The first was built in the grooves of a Pe- 

 ruvian torch-thistle as thick as my leg; the 

 second rested on a stalk of the opuntia, the 

 Indian fig. Had the fierce armour of these 

 two stout cactuses attracted the attention of 

 the insect, which looked upon their tufts 

 of spikes as furnishing a system of defence 

 for its nest? Perhaps so. In any case, 

 the attempt was not imitated; I never saw 

 another installation of the kind. There is 

 one definite conclusion to be drawn from my 

 two discoveries. Despite the oddity of 

 their structure, which is unparalleled in 

 the local flora, the two American importa- 

 tions did not compel the insect to go through 

 an apprenticeship of groping and hesitation. 

 The one which found itself in the presence 

 of those novel growths and which was per- 

 haps the first of its race to do so took pos- 

 session of their grooves and stalks just as it 

 would have done of a familiar site. From 

 the start, the fleshy plants from the New 

 World suited it quite as well as the trunk 

 of a native tree. 



166 . 



