620 DIPTERA. 



Some two-winged flies deposit their eggs in the stems, 

 buds, and leaves of plants, thereby producing large tumors 

 or galls, wherein their young reside. Others lay their eggs 

 in fruits, on the pulp of which their maggots live. These 

 gall and fruit flies belong to a family called Ortalidians 

 (ORTALIDIDJE), from a word signifying to flap or shake the 

 wings ; for they keep their wings in motion nearly all the 

 time, jerking them up and down, and twisting them round 

 so that the thick outer edges often come together. Some 

 of them are in the habit of suddenly raising their wings 

 perpendicularly above their backs, and running along a few 

 steps with them spread like the tail of a peacock. These 

 insects, together with several other groups of flies, differ from 

 all the foregoing in many respects, although they agree with 

 them in their transformations. The forehead is broad in 

 both sexes ; their winglets are very small or entirely want- 

 ing ; their powers of flight are feeble ; and they are rarely 

 found sporting on flowers in the sunshine, but seem generally 

 to prefer shady and damp places. 



The wings of the Ortalidians are often beautifully varie- 

 gated, striped, or spotted with shades of brown or black. 

 The hind body in the female generally ends with a pointed 

 tube, wherewith the eggs are deposited. The little white 

 maggots often found in over-ripe whortleberries, raspberries, 

 cherries, and other fruits, are the young of some of these 

 insects. Swellings, or galls, as large as a walnut, are often 

 seen on the stems of some of our native asters or starworts. 

 They are caused by the punctures of a fly, which lays its 

 eggs, singly, in the stem, when the latter is tender. The 

 puncture is followed by a spongy swelling, wherein the 

 maggot, hatched from the egg, lives, and passes through its 

 transformations. The insect finally comes out in the fly 

 state, through a small hole previously made in the gall by 

 the maggot. This fly may be called the gall-fly of the star- 

 wort (Tepkritis Asteris). Its body is about one fifth of an 

 uich long ; it is of a light yellowish-brown color, with paler 



