THE HOLLY-FLY 17 



It is not difficult to rear leaf-mining insects in captivity. 

 A wide-mouthed bottle, with a little damp earth or sand, 

 suffices for some ; or you may stick the cut end of the 

 plant into wet sand, and cover all with a glass shade. 

 Some of the moths or flies will come out after a few 

 summer weeks ; others must be kept all through the 

 winter. Do not be satisfied with rearing the winged 

 insect and making out its name ; that is only a prelimi- 

 nary. Try to investigate the structure and habits of the 

 larva. Think over the various difficulties which it has to 

 face, and then see for yourself how those difficulties are 

 overcome. The work, though not to be called easy, has 

 a fascination which is strengthened by experience. In- 

 stead of giving more advice, a drug of which the patient 

 soon tires, I will give, an example. The next lesson con- 

 tains an account of what I have been able to make out 

 concerning the history of a very wide-spread leaf-miner, 

 the holly-fly. 



V. THE HOLLY-FLY. 



The holly- trees in my garden and in the hedges around 

 are regularly mined by the larva of a two-winged fly. In 

 spring, summer and winter many a holly-leaf is seen to 

 be blistered, the blister sometimes extending over a con- 

 siderable fraction of the upper surface. When the blister 

 is opened with a needle, one or two minute yellowish- 

 white larvae, with black heads and tails, are found within. 

 They pupate in April or May, and form flattened oval 

 cases, of a rusty colour, and smooth, shining surface. 

 Each case shows a number of regular transverse lines, 

 which mark the segments of the larva, for this is one of 

 the very numerous Dipterous insects which form their 

 outer pupa-case from the dry and contracted larval in- 

 tegument. 



In June the fly is ready to become free and lay its eggs 

 in the young leaves. But how can the fly, which is minute 



B 



