The Theory of Parasitism 



I call for a scion of the Mason-bee of the 

 Sheds who shall live by the art of breaking 

 through ceilings. Until they show me one, 

 the theorists will only make me smile when 

 they talk to me of erstwhile workers relin- 

 quishing their trade to become parasitic slug- 

 gards. 



I also call, with no less insistence, for a 

 descendant of the Three-horned Osmia, a de- 

 scendant given to demolishing party-walls. I 

 will describe presently how I managed to 

 make a whole swarm of these Osmiae build 

 their nests on the table In my study, in glass 

 tubes that enabled me to see the inmost se- 

 crets of the work of the Bee. For three or 

 four weeks, each Osmia is scrupulously faith- 

 ful to her tube, which is laboriously filled 

 with a set of chambers divided by earthen 

 partitions. Marks of different colours painted 

 on the thorax of the workers enable me to 

 recognize individuals in the crowd. Each 

 crystal gallery is the exclusive property of one 

 Osmia; no other enters it, builds in it or 

 hoards in it. If, through heedlessness, 

 through momentary forgetfulness of her own 

 house in the tumult of the city, some neigh- 

 bour so much as comes and looks in at the 

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