188 THE BLOWFLIES OF NortH AMERICA 
length; first sternite large, following sternites successively 
smaller. Fifth sternite (pl. 21, B) as illustrated. 
Genital segments with internal anatomical features (pl. 21, 
A and C) as illustrated. 
Female. Head height 11.5; eye height 7.6; head width 15.5; 
length at antenna 8.0 and at vibrissa 7.0; bucea 0.34 eye height; 
front at narrowest (at vertex) 0.30 head width, 0.42 at lunule; 
frontale approximately 0.70 frontal width, and usually with 
interfrontal bristles; parafrontale and parafaciale usually with 
dull bronzy golden pollen; outer vertical bristles about two- 
thirds as long as inner ones; frontoorbital bristles two proclinate 
and one reclinate; parafaciale at middle one-half as wide as 
elypeus and wider than distance between vibrissae in proportion 
2.4:1.8 opposite lunule. Abdomen usually with heavier white 
pollen than in male. Otherwise similar to male except for normal 
sexual differences. 
Length. 6-10 mm. 
Distribution. Nearetic: Northern United States and southern 
Canada; apparently most abundant in the northeastern Great 
Plains region. 
No differences have been found to support the distinctness of 
the variety avium asiovora Shannon and Dobrosecky, which was 
based upon one male from the state of Washington in the U. S. 
National Museum. As stated by Shannon, this variety is darker 
in color than the typical avium, the basicosta is lighter in color, 
the mesonotal hairs are longer, and the outer forceps are some- 
what truncate apically. A long series of specimens from Mon- 
tana exhibit characters intermediate between the typical avium 
and its supposed variety asiovora. Northwestern and northern 
specimens of most ecalliphorids often are darker in color, the 
orange parts therefore appearing lighter by contrast. The hair 
of northern specimens is often longer, thinner, and more erect. 
In spite of these apparent differences I hesitate to use the varietal 
name until additional material has been examined. 
Biology, habits, and immature stages. Eggs are deposited in 
small masses in newly constructed nests of passerine birds. The 
individual egg is apparently undescribed. 
Larva. Third instar: Length 10-15 mm., greatest diameter 
3-5 mm., of typical blowfly larva habitus, creamy white to 
slightly brownish in color, usually with an internal reddish 
tinge when first collected due to presence of avian blood. Each 
segment with integument covered with numerous minute single- 
pointed spines, these longer on anterior segments and especially 
abundant and longer along segmental margins; first segment 
