EUBY-TAILED FLIES. Ill 



nlack insect, measuring less than an inch across the fore wings, 

 with a very small abdomen on a long petiole, and enormous hind 

 legs, nearly twice as long as the whole body. On the other hand, 

 several other genera are remarkable for the extraordinary length 

 of the abdomen of the female ; thus the North American Pelecinus 

 Politurator, Drury, is a shining black insect, measuring about an 

 inch and a half across the wings ; but the abdomen is very slender, 

 and composed of very long joints, the last only being short and 

 pointed ; the entire insect not measuring much less than three 

 inches in length. The hind legs are also long, and the tibise dilated. 



Family VII. — Chrysididce. 



Body nearly cylindrical ; abdomen with a very short peduncle, 

 and composed of from three to five segments, one of which is often 

 much larger than the others, and the last of which is often fur- 

 nished at the extremity with a series of large teeth, varying in 

 number according to the species ; the terminal segments of the 

 abdomen form a retractile tube, furnished at the extremity with a 

 small imperfect sting ; and the body is hard, and the abdomen 

 concave beneath, so that the insect, when alarmed, doubles its 

 abdomen beneath it, and rolls itself up into a more or less globular 

 form. 



The Ruby-tailed Flies are among the most brilliant of all the 

 Hymenoptera, most of the species being either of an intense green, 

 blue, or fiery red. They are small or moderate-sized insects, 

 which are found on walls or flowers in the full heat of the sun ; 

 for, as a rule, the most brilliantly coloured insects are diurnal in 

 their habits. As far as their habits are known, they deposit their 

 eggs in the nests of other insects (chiefly Hymenoptera), on the 

 larvse of which their own oiFspring feed. The European species 

 are very numerous, and are divided into a considerable number ot 

 genera; but the exotic Clirysididcc are still rather imperfectly 

 known. Chrysis Ignita, Linn., the commonest of the European 

 species, varies very much in size and colour, as well as in the 

 length and position of the four teeth at the extremity of the 

 abdomen. It is either blue or green, or suffused with copper, 

 or even considerably varied with black. The late Mr. F. 

 Smith suggests that its extraordinary variability may be 

 due to variation in food, as it is parasitic on several genera 

 of Hymenoptera of different sizes and habits {Vespa, Odynerus, 

 Cerceris, etc.). 



