THE RUBY-TAILED fUES. 331 



hy a very sliort foot-stalk. In consequence of the mode by 

 which tlie abdomen is attached, the insect is able, when alarmed, 

 to roll itself up into a ball, in which it is aided by the shape of 

 the abdomen, the under surface of which is concave so as to 

 receive the tliorax. At the end of the retractile tube, is a 

 small, sting-like ovipositor, capable, as I can testify from ex- 

 perience, of inflicting- a emart prick when the insect is moved 

 to anger. There is, however, no poison-gland, so that the prick, 

 though it may startle, cannot injure. 



The Ruby-tailed flies are among- the most beautiful of our 

 insects, and if they were only enlarged, might challenge the 

 most gorgeous productions of the tropics for brilliant splendour. 

 The head and thorax are coloured with vivid blue or green, 

 and the abdomen is of a fiery ruby, looking, as the insect flits 

 about in the sunshine, as if made of burnished metal. Five 

 genera of these insects are known to inhabit England, contain- 

 ing altogether about twenty-four species. They are all para- 

 sitic upon other insects, mostly affecting- the larvjE of solitary 

 Hymenoptera, among which the well-known Sand-wasp (Ody- 

 n&riis) is so frequently the victim that Dr. Chapman, who has 

 paid great attention to the Chrysididse, states that 'the de- 

 struction caused by Chrysididse amongst the young brood of 

 Odynems spinipes, roughly measured by the cocoons collected 

 last winter, is in the proportion of one to three of those of the 

 wasp.' The mode in which these paiasitic insects achieve their 

 task is so well narrated by Dr. Chapman that I cannot do better 

 than quote his own words. 



' On July 1 7th I observed a nest of Odynems paiietum, with 

 one cell open, and containing a nearly complete supply of 

 Lepidopterous larvos. A Chrysis ignita, flying about, settled 

 beside the cell ; and, after a brief examination with her 

 antennoe, wheeled round, and introducing her abdomen into 

 the cell, rested for about twenty seconds, doubtless in the act 

 of oviposition. I now regret that I did not then examine the 

 contents of the cell, in order to ascertain the fate of the egg 

 of Odynerus parietum. Three-quarters of an hour later, 

 Odynerus parietum had closed the cell with the usual earthen 

 pellets. Two days afterwards I examined this cell, when I 

 found a larva of Chrysis ignita a quarter of an inch long, 

 together with the Lepidopterous larvne stored by the wasp, but 



