328 



CHAPTER OF VARIETIES. 



the place, from which I conceived that, probably, it was a widowed 

 mate, and if so, that circumstance might account for the eggs being 

 laid in a hollow trunk, instead of a nest being built to receive them in 

 a bank, as it might have found the task of nest-building impossible for 

 itself to accomplish without assistance ; and it might, therefore, have 

 sought a depository ready made. I am sorry that I have no redbreast's 

 nest containing oak-leaves in my possession, to send herewith, but 

 should I hereafter meet with a specimen I will forward it to you, that 

 the question may be at once decided by occular demonstration, which 

 is always, to the naturalist, more valuable than a thousand printed 

 affirmations. 



SOLITARIUS. 



London, April 1833. 



On microgaster alvearius. — In addition to the facts connected 

 with the history of this very interesting parasitic fly, with which I have 

 already furnished you, I am now enabled to add the following : — On the 

 15th of last October, I observed upon a wall at Hampstead, several 

 caterpillars of the cabbage-white butterfly (Pontia Brassicce) most of 

 which were resting upon the yellow silken cocoons spun by those 

 parasitic grubs which had previously inhabited and fed upon their bodies. 

 There were, I should suppose, about twenty caterpillars which had 

 been thus attacked, and 1 could only find three which appeared t& have 

 escaped. The latter I brought home with me, expecting to rear the 

 perfect insects, but in this I was disappointed, for they had not 

 been many days in my boxes before they died, having disclosed several 

 similar parasitic grubs, which immediately spun their cocoons, which I 

 kept until they hatched. On the 15th of the present month (May) 

 they appeared in their winged state, and upon comparing them with 

 those which came out of the spider's egg (figured at page 180), I found 

 them to be of the same species. Now, it is a very extraordinary cir- 

 cumstance that those grubs which were deposited in the eggs of the 

 spider never spun any cocoons, but were disclosed as perfect flies, and 

 we may ask what became of the silk with which nature supplies them 

 for that purpose ? Is it probable that the reason of the fly's undergoing 

 its transformation inside the eggs instead of coming out for that purpose 

 as is usual, was in consequence of its not having the strength, when in 

 the state of a grub, to force its exit through the shell, owing to its 

 being bound round with silk, and obliged patiently to remain within 

 until it acquired the power or implements necessary to remove the 



