286 INSECT ARTIZANS AND THEIR WORK 



out in this connection. The first is the possibility 

 of so fine an instrument being capable of piercing 

 solid wood ; the second is the exactitude with 

 which the boring is made so that an egg can be 

 placed right in the tunnel of the Sirex. Unless 

 this could be accomplished all the labour of boring 

 would be in vain. Unless the Rhyssa grub on 

 hatching is in a position to get quickly to its prey 

 it must perish. It may happen that whilst the 

 Rhyssa is feeding upon its victim the Sirex grub 

 burrows deeply into the wood ; but having passed 

 through the intervening stages to the winged 

 condition it is then able to excavate a direct way 

 out to the air by means of its jaws. 



It is somewhat sad to relate that some species 

 of the honourable family of bees have fallen into 

 evil courses and are now to be reckoned permanently 

 among the insect criminal class. The bees of the 

 genus Osmia are industrious little insects that 

 construct their cells in blackberry-stems, empty 

 snail-shells, and similar retreats. Osmia leucomelana 

 when busy burrowing the blackberry-stem is 

 watched by another bee, Stelis minuta ; and wheri 

 Osmia is piling up her provisions Stelis slips in 

 and deposits an egg long before the heap is com- 

 plete. Osmia's own egg is not laid until the cell 

 is fully provisioned and ready for sealing up ; so 

 that the Stelis egg hatches first, and the two grubs 

 (Stelis and Osmia) are at opposite ends of the 

 pollen-mass. Ultimately, when the pollen is con- 

 sumed they meet, and Stelis, having always the 



