348 THE BLOWFLIES oF NortH AMERICA 
single labial sclerites, elongate, not strongly curved, the basal 
portion only lightly selerotized, and with a _ well-developed 
‘‘hatehing spine.’’ Amphipneustic, posterior spiracles lightly 
sclerotized, each with two more or less united slit-like apertures. - 
Second instar: Length 2-5 mm. Cephaloskeleton (pl. 46, D) 
strongly sclerotized, the labial sclerites short, strongly hooked 
and paired; the dorsal cornua anteriorly prolongated. Anterior 
spiracles each with four apertures, posterior spiracles (pl. 46, F) 
each with two well-separated slitlike apertures. 
Third instar: Length 6-12 mm. Mostly smooth. Anal segment 
with eight protuberances, only the anal pair strong. Cephalo- 
skeleton (pl. 46, E) strongly sclerotized, the labial sclerites 
strong, long, and curved; dorsal cornua weak, elongate, both an- 
teriorly and posteriorly prolongated; ventral cornua heavily pig- 
mented and strongly sclerotized. Anterior spiracles (pl. 46, G) 
each with four apertures, posterior spiracles (pl. 46, H) each 
with three well-defined slithke apertures, rather lightly sclero- 
tized, the ‘‘button’’ in peritreme. 
Keilin (1909 and 1915) stated that eggs of Pollenia rudis are 
deposited in soil toward the latter part of August or early in 
September and hatch in from 4 to 6 days. The first-instar larva 
enters the earthworm host by the male genital orifice and then 
passes into the body cavity of the genital segments, probably 
during copulation. The parasite then supposedly remains dor- 
mant in the body cavity of the host from September or October 
until the following April or May, when it becomes active and 
migrates to the anterior end of the host. When it arrives at the 
prostomium, the posterior spiracles become exposed to air and 
the larva begins feeding upon the anterior segments of the worm. 
Six to 10 days later, it molts. The second stage requires 9 days. 
In the final instar, the parasite feeds aggressively on all tissues 
of the host, then leaves the host, which is still alive, and pupates 
in the soil. The pupal stage lasts from 39 to 45 days. 
In the United States, phases of the biology of this species 
have been reported as follows. Eggs are deposited in suitable 
locations in soil by over-wintering females as soon as spring tem- 
peratures have reached 80° F. Two or three eggs are usually 
deposited within a few inches of each other. Individual females 
have deposited as many as 97 eggs in one day according to 
DeCoursey (1932), who stated that there is apparently no ovi- 
position stimulus derived from the presence of earthworms in 
the soil. He found that adults deposit eggs upon many different 
materials but never upon carrion. 
| DeCoursey (1927) found that the larva enters the host through 
