218 LEAF-MINING INSECTS 



to bluish-gray and sometimes tinged with yellow. The 

 thoracic legs are four- jointed with a broad basal and a 

 narrower second segment. The seven pairs of prolegs are 

 short, blunt and little used. At least on the younger larvae 

 are brown to black, chitinous spots on the dorsal side of the 

 prothorax and on the ventral side of all the thoracic seg- 

 ments. In the later instars the larvae are rather stout and 

 dilate the upper sides of the mines. 



When about full-grown they eat out the parenchyma from 

 a part of the leaf at one border of the mine making an out- 

 pushing a little more than 6 mm. in diameter. There they 

 spin lens-shaped cocoons which on one side are applied to 

 the upper cuticle of the leaf. This cuticle is gradually cut 

 through at the border of the cocoons and presently the cases 

 with their covering of leaf epidermis on one side and their 

 thin sheet of weaving on the other are freed from the leaves 

 and fall to the ground. All the frass and cast skins are left 

 outside the cases which are semi-transparent, revealing the 

 larvae within. Somewhat flattened though the larvae be 

 they cause the walls of the cocoons to bulge. On the ground 

 the cases look not unlike little seeds. The deserted leaves 

 present a peculiar appearance with mines of which the lower 

 walls are intact, while the upper walls have every one a neat 

 round piece removed. 



In these cases on the ground the larvae remain until the 

 following season in late March or early April when they 

 assume the pupal state. In the months after leaving the 

 leaves they are said to be able to cause their cocoons to 

 hop on the ground by their powerful movements within. 

 Professor Ritzema Bos says that they sometimes jumped 5 

 to 10 mm. off the ground and C. Healy makes the statement 

 that they move on the ground by little hops. They are 

 also moved passively by the wind. That they are some- 

 times very abundant locally is suggested by the somewhat 

 remarkable statement of Mr. McLachlan (Proceedings 



