LIFE HISTORIES OF MUSCA AND ALLIES. 39 



are required for tlie entire developiiient from egg to 



imao-o. 



These stages are illustrated in Plate IV., Figs. 8 and 9. 



The rapid changes following so rapidly in generation 

 after generation make it impossible for the student to sep- 

 arate broods, and it is therefore easj to account for the 

 immense numbers of house flies Mhich are everywhere and 

 always present. Even in years when flies are, by com- 

 parison with former seasons, said to be scarce, they are 

 still present in sufficient numbers to be safely considered 

 the most plentiful insect in America. Harrington ^^ in a 

 readable, popular account quotes Linne to the effect that 

 three flesh flies "with their progeny could eat up a dead 

 horse as quickly as a lion could." This truth, impossible 

 as it seems at first, coming as it does from the great nat- 

 uralist, explains why, when the season ftivors and its 

 natural enemies are greatly abated in numbers, these in- 

 sects — the whole tribe of ]\Iuscina? — are to be found in 

 swarms defying computation. S. A. kStewart ^^^ speaks of 

 a "plague of flies" in Ireland in 1878, so extensive that 

 stones and plants for about one and a half miles along 

 the Bann were completely covered Avith the pupa cases, 

 from which "they issued in millions and attacked both 

 men and cattle." In a few days the ground was strewii 

 with the dead flies, in some places lying three inches deep. 

 J. H. Smith ^^® writes of a column of flies, thought to be 

 M. domestica, issuing from a crack in the wall of the 

 palace at Delhi, India. In a band about seven inches 

 wide they marched out of the shadow of the building, 

 and as soon as their wings dried in the warm sunlight 

 took flight. They could not be made to alter their course 

 by any form of tormenting or destruction which occurred 



