ANTS, WASPS, AND BEES. 219 



billions, a number for the support of which all the 

 German forests would not be sufficient. 



The Saw-flies are so numerous and so common 

 that it would be easy to quote many examples, but 

 one or two instances must suffice. During the winter 

 months certain oval brown cocoons will be found 

 adhering to the twigs of the whitethorn. These are 

 the cocoons of an insect somewhat resembling a bee, 

 but with a longer body and legs. 1 It is of a blackish 

 colour, with ashy, orange hairs. By means of their 

 curious saw-like apparatus the females form small 

 channels in the tender branches where they deposit 

 their eggs, the larvae being hatched in August, when 

 they are of a pale dull-green colour. When alarmed 

 they discharge a clear, greenish, watery fluid from the 

 lateral pores, placed above the spiracles, to a con- 

 siderable distance. The object of this is evidently 

 to drive off parasitical enemies, in which it is not 

 always successful, for it is common to find the inside 

 of the cocoons filled with the small cocoons of an 

 ichneumon, sometimes of two different species, 

 which have flourished at the expense of their host. 



Another species with a black body and black legs, 

 frequents not only the plum and cherry, but also the 

 oak. 2 The slimy grub, after feeding to the full on 

 the leaves of these trees, descends into the ground to 

 undergo the change into the pupa state, and the 

 perfect fly makes its appearance at the end of July. 



In association with these may be named another 



1 Tenthredo ( Trichiosoma) htrorum. 



2 Selandria afra. 



