THE INSECT WORLD. 385 



very few, except small forms, which are quite usually metallic 



black, bronze, or green. The wings are without venation, except 



for a strong vein running parallel to the costal margin, but not 



reaching quite to the tip, and 



the antennae are geniculated Fig. 443. 



or abruptly bent at the end 



of the long first joint. Few 



of these have the ovipositor 



visible, and usually it lies in 



a groove on the under side 



of the tip of the abdomen, 



issuing before the apex. These 



Chalcidid flies are exceedingly , ,. ... 



. . Aphehnus mytilasptdis, parasite on scale 



numerous, and are parasitic on insects; much enlarged. 



a great variety of other insects. 



They are rather more robust in build than the other small para- 

 sites, and this fact, with their usually brilliant metallic coloration, 

 is a tolerably good guide to the family, of which the species in- 

 festing the common cabbage butterfly may serve as a good 

 example. If, early in the spring, a large number of chrysalids 

 of the cabbage butterfly be collected, — which can be easily done 

 along the fences bordering last year's cabbage-field, — it will be 

 found that some of them have a rather warm gray color and 

 move the joints of the abdomen freely, evidently showing life. 

 Others will have a peculiar, dead, straw-yellow color, and the 

 abdomen is brittle and will break rather than move. If it does 

 break, the interior of the chrysalis will be found completely filled 

 with little, greenish-gray, maggot-like larvae, in which the seg- 

 ments are well marked and a little darker in color. If such 

 infested chrysalids be removed to a warm room and kept in a 

 covered vessel, there will emerge in due time dozens of Pter^- 

 viahis pupariun, a greenish-bronze Chalcidid, instead of the 

 common white cabbage butterfly. 



Though these insects are minute, being scarcely one-eighth of 

 an inch in length, yet they are giants compared with others 

 which live in scales and even in the eggs of other insects. Very 

 frequently such Chalcidids are bred from galls, and they are here 

 either parasitic upon the actual gall-maker, or they may live in 

 '.he abnormal tissue produced by the Cynipid larvae. We find 



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