58 Tur Buowruies or NortH AMERICA 
necessary for their development, and they occasionally oceur in 
mixed garbage and other kinds of refuse. Although they develop 
normally in decomposing media, they are often injured by ex- 
cessive putrefaction. Thus, upon emerging from the egg, the 
larva feeds for a short time upon the surface of the food in the 
vicinity of the egg mass, then it bores into the comparatively 
fresh food within, preferring that to the putrid decomposing ma- 
terial outside. Wounds in which such species occur are usually 
old, pustular, and suppurative. With only few exceptions they 
have a tendency to feed outside a myiasis wound if the wound is 
in a long-fleece animal. 
Larvae of blowflies are extremely sensitive to ight and react 
negatively to it. The response becomes more marked with age. 
Ellsworth (1933) found that larvae of sericata were protected — 
from overstimulation by light through the retraction of the en- 
tire photoreceptor organ and the infolding of the chitinous 
-eollar. 
The effects of temperature and humidity upon larval develop- 
ment of several species were studied by Bishopp (1915), Herms 
(1928), Smit (1928), and Wardle (1930). Larvae of sericata be- 
come active when careass temperature reaches 50° to 55° F., 
according to Deonier (1940), and it is possible that the larvae of 
most species react similarly. 
Hydrogen ion concentration in the digestive tract of larvae of 
blowflies was studied by Hobson (1931) and Waterhouse (1940). 
These authors found the pH to be 7.0 in the crop, 6.5 in the an- 
terior portion of the midgut, 3.0-3.5 in the middle portion of the 
midgut, 7.5-8.3 in the posterior portion of the midgut, and 8.0- 
8.5 in the hindgut. The latter author found these pH values 
to be essentially similar in all species studied. 
DIAPAUSE. When fully developed, blowfly larvae leave 
their food and enter the prepupal stage. According to Mellanby 
(1938, p. 392) ‘‘The prepupa is externally indistinguishable 
from a larva, but it does not feed and it possesses other physio- 
logical properties.’’ After several days of favorable conditions, 
the larva becomes rounded and the skin becomes hardened to 
form the puparium. Under unfavorable circumstances, such as 
low temperature or lack of sufficient moisture, they are able to 
suspend pupation and may remain active for months without fur- 
ther apparent development. This cessation of development is 
called ‘‘diapause.’’ The diapause presumably ends when the pre- 
pupa has acquired sufficient water to overcome any effects of desi- 
cation and is stimulated to pupation by suitable temperature. 
