180 ZOOLOGY. 



emerges in August. Very considerable damage may 

 be done by the first generation, of which the habits 

 have just been described. During 1869 in Silesia, 

 from two-thirds to five-sixths of the ears in many 

 fields remained hidden in the leaf-sheaths, and conse- 

 quently gave no increase. The first generation of the 

 ribbon-footed corn fly can also develop in the way 

 described in the haulms of several grasses, e.g. in 

 species of Poa and Holcus. 



The flies, emerging in late summer, lay their eggs, 

 here, too, separately, on the leaves of grass or com. 

 Wherever possible, they seek out for the purpose the 

 winter wheat plants then present in the fields, but 

 also content themselves with rye, or even with wild 

 or meadow grasses ; they have to be satisfied with 

 grasses if, at the time of egg-laying, the winter corn 

 is not yet up. The maggot, when hatched, works its 

 way to the inner side of the leaf-sheath, and thence 

 to the apex of the still very small haulm ; there it 

 remains during the winter. The damage becomes 

 apparent the following spring. The growth in length 

 of the haulm in question is extremely small, while 

 growth in thickness increases to an abnormal ex- 

 tent. Almost all the leaves completely surround 

 the haulm, which swells to an enormous extent (Fig. 

 119), together with the enclosing leaf-sheaths, which 

 are much broader than usual. The unattacked plants 

 are naturally much larger than the sickly ones, and 

 deprive these of air and light, so that they die down, 

 being overshadowed, not only by the sound haulms, 

 but also by their own secondary shoots. The result- 

 ing damage may be tolerably great, especially at the 

 edges of the field. It may happen that both summer 

 and winter generations of the ribbon-footed corn fly 

 are harmful in the same distiict; but it frequently 

 happens that only one or the other is complained of 

 in a particular spot. It is only natural that the flies 

 which swarm around in May, and again in August' 



