230 THe BLOowFLIES oF NortH AMERICA 
and about twice as large as the median, the two inner tubercles 
separated by a distance greater than the distance between the 
inner and median tubercles and approximately equal to distance 
between inner and outer ones (as in mexicana); outer and 
median pairs on lower border large, approximately equal in size 
and much larger than inner pair; inner pair on lower lip smaller 
than outer pair on upper border; tubercles on anal protuberance 
slightly shorter and less pointed than the two outer pairs on 
lower border of stigmal field; segment 12 generally smooth to 
finely scabrous on dorsal surface. Posterior spiracles (pl.39,H) 
comparatively large, heavily pigmented, and with usual form; 
peritreme prominent, with well-developed inward projection be- 
tween outer and middle slits. Cephaloskeleton (pl.39,G) large 
and heavily pigmented; dorsal cornua broad and widely sep- 
arated from ventral cornua; at posterior end and below ventral 
cornua with a pigmented porous area, possibly representing a 
more heavily pigmented portion of the pharynx which is not 
conspicuous in other species of Luciliini here described; labial 
selerites pointed slightly upward and curved downward. An- 
terior spiracles with comparatively large prominent branches; 
external portion equal to or only slightly longer than stigmal 
chamber (pigmented portion of trunk); anterior spiracles gen- 
erally with 6 to 8 branches. Of 80 spiracles, 5 had 5 branches, 
23 had 6, 20 had 7, 22 had 8, and only 2 had 9. 
Puparwm. According to Bishopp (1915) the pupal stage lasts 
from 5 to 16 days in Texas during fairly warm weather. During 
periods of fairly high temperatures in Texas he found that the 
larval period lasted from 2 to 5 days and that the puparia were 
formed from 38 to 12 days after the hatching of the eggs. During 
periods of low temperatures, however, the third larval stage was 
sometimes extended to several weeks. 
Adult. In the Middle West alustris appears on the first warm 
days of spring, although a few adults may be collected in favor- 
able situations during protracted warm periods in midwinter. 
Wardle (1930) stated that this species formed 24 percent of the 
total blowfly population in Minnesota during July, August, and 
September in 1927. Overwintering of illustris is supposedly in 
the larval or the pupal stage, although the appearance of adults 
during midwinter may indicate hibernation in that stage under 
certain conditions. The preoviposition period is from 6 to 20 
days, according to Bishopp (1915); the flying range of the 
species was tentatively fixed at 3.5 miles by Bishopp and Laake 
(1921). 
It seems that allustris is an open woodland and meadow species. 
