H Y MEN OP TERA . 629 



side to the cup-like scale covering the base of the fore 

 wing ; the wings have no closed cells ; and the ovipositor is 

 usually hidden, issuing before the apex of the abdomen. 

 Figures 759 and 760 represent Chalcis-flies greatly enlarged. 



It is to this family that the great majority of the para- 

 sites of the smaller insects belong. Thus scale-bugs are 

 preyed upon by many species of Chalcis-flies. But Chalcis- 

 flies also attack large insects, for many caterpillars are de- 

 stroyed by them. The most efficient parasite of the cab- 

 bage-butterfly is a Chalcis-fly, Pteromalus puparum (Pte- 

 rom'a-lus pu-pa'rum). In the case of these larger insects 

 hundreds of Chalcis-flies may reach maturity within a single 

 individual. 



The larvae of Chalcis-flies usually feed within their vic- 

 tims, but a few live attached externally. Some Chalcis- 

 flies, like the members of the next family, are egg-parasites,, 

 and certain others are developed within the galls produced 

 by members of other families (Cynipidae and Cecidomyidae),. 

 and are doubtless merely inquilines, instead of parasites. 



The members of one subfamily closely approach the 

 gall-flies (Cynipidae) in structure and in habits. One of 

 these, the Joint-worm, Isosoma hordei (Is-o-so'ma hor'de-i),. 

 is a well-known pest, which infests the stalks of growing 

 grain. It causes a woody growth, which fills up the cavity 

 of the stalk, and sometimes also causes a joint to swell and 

 the stalk to bend and lop down. The presence of this insect 

 is often indicated by pieces of hardened straw coming from 

 the threshing-machine with the grain. There is but a single 

 generation of the joint-worm in a year. The insects remain 

 in the straw during the winter, the adults emerging in the 

 spring. Obviously the best way to destroy this pest is to 

 burn the infested straw before the insects emerge. 



The Chalcis-flies of the genus Leucospis (Leu-cos'pis) are 

 very remarkable in form. They agree with the true wasps, and 

 differ from all other Hymenoptera in having the fore wings 

 folded like a fan when at rest. They are also peculiar in 



