SUBFAMILY POLLENIINAE 347 
somewhat (from 0.44 to 0.50 in the female and from 0.29 to 0.42 
in the male). In most specimens the length of the head at the 
antenna is somewhat greater than the length at the vibrissa in 
the male, but several specimens have these lengths nearly equal. 
It may be possible, by extensive rearing, to show that more than 
one form of Pollenia occurs in North America; but it is difficult 
to prove specific limits with collected material. As stated by 
Townsend (1935, pp. 104-105), ‘‘What is ealled Pollenia rudis 
shows a great range of variation in several characters that are 
ordinarily of generic value, which condition may be interpreted 
as the probable result of an intermixture of two or more closely 
related forms long kept apart, but later fluxed as they spread 
and met on removal of the barriers that formerly existed between 
them.’’ 
Distribution. Holarctic: Central and northern Europe; North 
America, common from Virginia and Tennessee to Nova Scotia 
and British Columbia. It may be collected as far south as 
northern Florida and southern Georgia during warm winters. 
Séguy (1934) stated that rudis is common in middle Europe, 
rare in north Africa. 
Biology, habits, and immature stages. The species has been re- 
ported as a parasite of the following species of earthworms: 
Helodrilus roseus (Sav.), Allolobophora caliginosa (Sav.), and 
Allolobophora chloroticus (Sav.). It apparently will parasitize 
many species of earthworms, but the first named has been found 
to be the favored host in North America. Parasitism by Pollenia 
rudis upon earthworms was first recorded by Hoffmeister (1845). 
Egg. Described by DeCoursey (1927) (pl. 46, A and B) as 
follows: ‘‘ About 1 mm. long, 0.3 mm. in length, the ventral side 
convex, dorsal side flat or slightly concave; two carinae extend 
along the dorsal side almost to posterior end; surface with ex-. 
ception of two ridges and groove between them, is finely etched 
into irregular figures.’’ ; 
The duration of the egg stage in the vicinity of Washington 
was found to be approximately three days, according to Webb 
and Hutchinson (1916). 
Larva. The larva of Pollenia rudis has been described and 
figured by Keilin (1915) and DeCoursey (1927). 
First instar: 1.0 to 1.5 mm. in length, 0.2 to 0.25 mm. in 
diameter, with complete spinose bands anteriorly on segments 
1 to 4 and 11, and ventral anterior and posterior bands of larger 
spines on segments 4 to 12. Cephaloskeleton (pl. 46, C*) with 
*Redrawn from Keilin (1915, plate 7, figures 31, 32, 33, and plate 8, 
figures 36, 37, and 38) by the kind permission of Dr. Keilin. 
