568 Animal Biology 



a great variety of plants that it is difficult ever to destroy all of them in 

 a certain locality. The Mediterranean flour moth is a very common 

 and injurious pest, especially in flour mills. The cotton worm and the 

 cotton boll worm cause millions of dollars' damage annually to cotton. 

 The various types of tussock moths attack numerous forest, shade, and 

 fruit trees. The larvae of the grain moth bore into the grain of corn, 

 wheat, and rye. The larvae of the black swallow-tail butterfly eat 

 celery and parsley. 



licT^^ 



Pupa 



Ecjqs 



/VIqIg moth 



Larva 



Fig. 302. — European corn borer [Pyrausta nubilalis) of the order Lepidoptera. 

 The larva is the true borer in corn stalks and many other plants. The larva de- 

 velops into the pupa, which in turn develops into the adult moth. The eggs laid 

 by the female develop into the larvae. 



Order 20 — Diptera: The tachina flies are valuable enemies of leaf- 

 eating beetles, locusts, and caterpillars, particiilarly those of the army 

 worm. The common housefly, besides transmitting disease germs, such 

 as typhoid and tuberculosis, carries the eggs of several species of para- 

 sitic flatworms. They also destroy foods by depositing their eggs in 

 them. The horseflies attack horses, cattle, and human beings. The 

 flesh flies and blow flies deposit eggs in meats. The eggs under proper 

 conditions develop into maggots (larvae) which feed on the meat, thus 

 rendering it unfit for use. The bee flies resemble true bees somewhat. 

 Their larvae eat young grasshoppers, wasps, and bees, while the adults 

 feed on the nectar of flowers. The banana flies (one of the fruit flies) 

 are of great value for experimental studies in heredity. The adult flower 



