FORMS INJURIOUS TO HUMAN INDUSTRIES 351 



eggs " of this generation survive, lie dormant during the winter, 

 and wingless females hatch out from them in the following 

 spring. 



Scale- Insects {Coccidcs), of which one kind has already been 

 described (see vol. iii, p. 381), are particularly harmful in fruit- 

 culture. Well known in Britain are— Apple Scale {Mytilaspis 

 pomo7'nm), white woolly Currant Scale {Pulvmaria ribesicB), and 

 Gooseberry and Currant Scale {Lecanium ribis). 



Fringe -Winged Insects {Thysanoptera). See vol. i, p. 355. 



Flies {Diptera). — The most familiar pests belonging to this 

 group are the Crane-Flies or " Daddy- Long- Legs " {Tipulidcs), of 

 which there are at least some thirty 

 British species. The larvse, known 

 as " leather - jackets ", are very de- 

 structive to the roots of grasses and 

 cereals (fig. 1248). A species which 

 has been responsible for great damage 

 to cereal crops in America is the 

 Hessian Fly {Cecidomyia destructor), 

 so called because it is supposed to 

 have been introduced into the New 

 World in 1778 by means of straw 

 brought by Hessian mercenaries. 

 The female fly lays her eggs in 

 pairs in the angles where the leaves 

 of wheat, barley, or rye join the 

 stem. The maggots feed upon the juices of the haulm, causing 

 this to bend or break, and interfering greatly with the develop- 

 ment of the grain. The Wheat- Midge {Cecidomyia tritici) is 

 chiefly destructive to wheat and rye, the eggs in this case being 

 laid in the flowers. The Frit-Fly {Oscinis frit) is injurious to 

 cereals in much the same way as the Hessian Fly, but its eggs 

 are here laid on the under sides of the leaves. Some flies lay 

 their eggs on food, and cause great annoyance. The Blow- Fly 

 or Blue-Bottle {Musca vomitoj^id) and the Cheese-Fly [Piophila 

 casei) are well-known examples. 



Moths and Butterflies [Lepidoptera). — Almost everyone has 

 noticed the way in which the caterpillars of these insects vora- 

 ciously devour plants of various kind, and a mere list of destructive 

 species would occupy a considerable space. Among injurious 



■Cran^-FXy [TiJ/ula olerac{s). i, Larva; 

 2, pupa; 3, adult: 4. eggs. 



