INTRODUCTION ; 17 
rect in his assumption that blowfly larvae could multiply by 
paedogenesis although Keilin (1924), after conducting careful 
and extended experiments, concluded that paedogenesis does not 
oeceur in Calliphora. 
EFFECT OF BLOWFLIES ON WILDLIFE. Certain spe- 
cies of blowflies are parasitic upon birds and others upon animals. 
Apaulina metallica is found in large numbers in nests of the bank 
swallow and Stoner (1936) stated that the bloodsucking parasitic 
larvae of this blowfly were the most injurious external parasites 
of the bank swallow in New York State. There are many refer- 
ences in the literature upon the effects of Callitroga americana 
and other blowflies upon game animals. No North American 
mammal, large or small, is exempt from myiasis caused by the 
larvae of this species. Pollenia rudis and species of the genus 
Onesia are obligate parasites of earthworms and the economic 
effect of such species is difficult to ascertain. 
FINANCIAL LOSS. In the southern part of the United 
States one species of blowfly (americana) causes a loss of from 
4 to 10 millions of dollars each year in the state of. Texas 
_ (Bishopp, 1934). According to Belschner (1937) the sheep blow- 
fly (Phaencia cuprina Wiedemann) costs Australia nearly 20 
millions of dollars annually. He states that ‘‘with the single 
exception of drought, the sheep blowfly is probably the biggest 
problem with which each Merino sheep breeder has to contend.’’ 
The advent of the automobile and the moving of stables and 
dairies into the country has caused a great reduction in the 
abundance of houseflies and stableflies in urban centers. Such 
flies are now of relatively minor importance in larger cities 
except in the vicinities of zoological parks, riding academies and 
markets. The reduction in the number of these flies is largely 
attributable to the excellence of modern systems of municipal 
sanitation and public health supervision. But the number of 
blowflies in urban centers has not been decreased in the same 
proportion. 
It has been estimated by Hyslop (1938, p. 48) that 26 millions 
of dollars are spent each year in the United States for the control 
of flies. This total included only sums spent for screen wire 
and sprays. The public does not differentiate between different 
species of flies. These 26 millions of dollars wo:th of wire 
screening and sprays are purchased for the purpose of keeping 
all sorts of insects from buildings. A considerable proportion of 
this amount is spent obviously for the purpose of keeping blow- 
flies from homes, stores, and packing establishments. 
The discarding of maggot-infested meats in packing industries 
