THE ADVENTURES OF A GRUB 109 



establishment is used by two kinds of Bee, the Anthophora 

 and the Osmia. 



The Anthophorae are the actual pioneers. The work of 

 boring the galleries is wholly theirs, and their cells are right 

 at the end. If they, for any reason, leave the outer cells, 

 the Osmia comes in and takes possession of them. She divides 

 the corridors into unequal and inartistic cells by means of 

 rough earthen partitions, her only idea of masonry. 



The cells of the Anthophora are faultlessly regular and 

 perfectly finished. They are works of art, cut out of the 

 very substance of the earth, well out of reach of all ordinary 

 enemies ; and for this reason the larva of this Bee has no 

 means of spinning a cocoon. It lies naked in the cell, whose 

 inner surface is polished like stucco. 



In the Osmia's cells, however, means of defence are required, 

 because they are at the surface of the soil, are roughly made, 

 and are badly protected by their thin partitions. So the 

 Osmia's grubs enclose themselves in a very strong cocoon, 

 which preserves them both from the rough sides of their 

 shapeless cells and from the jaws of various enemies who 

 prowl about the galleries. It is easy, then, in a bank in- 

 habited by these two Bees, to recognise the cells belonging 

 to each. The Anthophora's cells contain a naked grub : 

 those of the Osmia contain a grub enclosed in a cocoon. 



Now each of these two Bees has its own especial parasite, 

 or uninvited guest. The parasite of the Osmia is the black- 

 and-white Fly who is to be seen so often at the entrance to 

 the galleries, intent on laying her eggs within them. The 

 parasite of the Anthophora is the Sitaris, the Beetle whose 

 corpses appear in such quantities on the surface of the bank. 



If the layer of Osmia-cells be removed from the nest we 

 can observe the cells of the Anthophora. Some will be 

 occupied by larvae, some by the perfect insect, and some 

 indeed many will contain a singular egg-shaped shell, divided 

 into segments with projecting breathing-pores. This shell is 

 extremely thin and fragile ; it is amber-coloured, and so 



