DIPTKRA OF xMINNESOTA. 23 



are described at greater or less leng-th, emphasizing the two-winged 

 pests of Alinnesota. A very common misatke of the uninitiated, 

 when large and small flies are observed together, — on a window, 

 for example, — is to regard the small flies as the young of the larger 

 ones. This is not so, like insects of other orders, flies never in- 

 crease in size after having attained the winged or perfect stage, 

 and the small flies observed are the adults of species different from 

 the larger species. In other words, flies only increase in size dur- 

 ing the larval or "maggot" stage, at which time they, like other 

 larval forms, have a voracious appetite. They are maggots, there- 

 fore, which the farmer squeezes out of the small holes on the back 

 of his cattle, maggots which issue from a horse with the droppings 

 when he has the "bots," and maggots which are sometimes found 

 in open wounds of stock running in pasture. We are all familiar 

 with the maggot or larval stage of the blow fly, seen on meat which 

 has been exposed to its attacks. It should also be recognized that 

 it is in the maggot stage in which the Hessian fly, joint worm fly and 

 frit fly work injury. Maggots are footless, and many are provided 

 with two tiny hooks in the mouth, probably the mandibles or jaws. 



With a few exceptions where maggots are produced alive di- 

 rectly from the parent, or where, very rarely, a maggot brings 

 forth living maggots, or a pupa lays eggs, every maggot comes 

 from an egg laid by the adult female fly upon the plant or animal 

 or other substance which is to furnish food for the larva. Familiar 

 examples of flies' eggs are seen on meat, as intimated above, and in 

 the "nits" which the bot fly so skillfully fastens to the hair of horses. 

 We also see the white eggs of parasites attached to caterpillars, 

 from which eggs the tiny maggots hatch, and at once bore into 

 the tissues of their host. 



When a maggot has attained its full growth, it changes to what 

 is known as a "pupa," in which, with a few exceptions, it remains 

 inactive for a period, until it transforms to the perfect fly. Fre- 

 quently in forming this pupa the skin of the maggot contracts, 

 turns brown and hardens, thus forming a pupal case or puparium, 

 in which the maggot transforms to the pupa, and from which the 

 changed pupa, or perfect fly, emerges later. It is these puparia 

 which one sees in the earth about stalks and cabbages or cauli- 

 flowers — elliptical, brown bodies from which the perfect cabbage 



