70 Second Report on Economic Zoology. 
Life-history of the Cabbage Root Fly. 
The fly Phorbia brcissicas (Fig. 9, a), the parent of the Cabbage 
Root-maggot, belongs to the family of two-winged insects (or Diptera) 
known as Anthomyidae. It in general resembles a “ house-fly,” but is 
rather smaller in size ; its body is about a fourth of an inch long. The 
male is dark ashy -grey with three broad dark stripes on the surface 
of the thorax and a wide dark dorsal stripe on the abdomen, dilated 
at the upper margin of each segment, which is marked with a narrow 
transverse dark stripe ; the whole body is bristly and the eyes nearly 
meet in the middle of the head ; the legs are black and very bristly, 
with a prominent tuft of bristles at the base of each hind femur 
below. The female is paler ashy -grey, with very indistinct thoracic 
and abdominal stripes, often absent, and the eyes are widely separate, 
and the apex of the abdomen is pointed. The female has not such 
marked characters as the male, and can only be identified by the 
specialist. 
The flies appear first of all at the end of April and on to May. 
I have seen them in warm weather as early as April 20th. They 
also occur in June, and successive broods appear later. Certainly 
two and probably three generations occur during the year. If there 
are no cabbages to oviposit on then they place their eggs on wild 
crucifer roots. 
The female creeps down into the earth around the plants and 
places her eggs in clusters close to or upon the roots, using the 
extensile ovipositor to aid her in this process. At other times they 
are laid (if the ground is firm and close) on the soil close to the 
plants. Apparently fifty-five is the normal number of eggs laid by 
each female (Slingerland). 
Fig. 9. 
a, The Cabbage Root Fly ( Phorbia brassicas, Bouche) ; b, the puparium. 
