IZ 8 NORTH AMERICAN DIPTERA. 



ally furcate; anterior cross- vein very near the root of the 

 wing, often appearing as the beginning of the third vein, 

 the real origin of the third vein having the appearance 

 of a short cross- vein; only one basal cell present. 



The family Cecidomyidae includes a very large number 

 of frail, delicate, often very minute flies, but is of the 

 greatest interest to the biologist as well as the economic 

 entomologist. At present about 600 species are known 

 from Europe alone. 



The egg of the Cecidomyidae is somewhat elongated, 

 rounded at both ends, orange-yellow or white in color. 

 The time required for hatching is very variable and de- 

 pends upon the weather, sometimes requiring a very few 

 hours, but more generally a few days or even weeks. 

 The larval food is almost wholly vegetable. The larvae 

 of some species have been bred from decaying wood and 

 bulbs, others from under the bark of trees, or from fungi. 

 But the great majority prefer living plants, attacking 

 the soft and green parts. Most of the larvae are mono- 

 phagous, living almost exclusively on a single kind of 

 plant, or at least closely allied plants; but there are cer- 

 tain exceptions, such as C. sisymbrii, which is said to 

 form the gall in spring on the barberry, and later in the 

 season on a nasturtium. There are certain others which 

 are inquilinous, that is guests or parasites in galls formed 

 by other Cecidomyids. Finally, some live parasitically 

 in the society of plant lice. Not a few, such as the Hes- 

 sian fly, live upon the surface of plants, or in the axils 

 of their leaves; but the greater number penetrate inside 

 the plant, producing the so-called galls. Every part of 

 the plant from the root to the flower and the fruit is lia- 

 ble to such attacks. With a few rare exceptions, each 

 species attacks the same part of the plant and deforms it 

 in the same manner. The galls cause deformations and 

 excrescences attached to the stalk, stems, or flowers, de- 



