20 : TRANSACTIONS OF THE 
fibres and tiny stones which forms a plug one-half to 
three-fourths of an inch long. 
But however efficacious her precautions may be 
against certain members of the parasitic hymenoptera, 
they are unavailing against her own relatives, little grey 
bees of the family Stelididae which enter the burrow 
while the bee is away after pollen and deposit their eggs 
in the mass of pollen intended for the Osmia larvae. 
