142 Flies [cH. 
withers. On pulling up one of these plants we find 
that the main root is decaying and very few fibrous 
roots are left; burrowing in the decaying root or at 
the base of the stem are a number of fly maggots. 
These are about 4 inch long when full grown, and 
whitish in colour. The front end is pointed and carries 
a pair of hook-like jaws. Behind the head are a pair 
of much branched spiracles. The tail end is blunt and 
carries a number. of projections which enable us to 
recognize it (see Fig. 43.4). The eggs from which the 
maggots hatch are laid just below the surface of the 
soil, on or very close to the plants. On hatching they 
begin to eat the outer layer of the root and reaching 
the inside feed on the softer portions. They also make 
it possible for other organisms to enter, thus hastening 
the decay of the roots. 
When fully grown the maggots change to brown 
puparia (see Fig. 43 B) usually in the soil, but occasion- 
ally in the roots. In about a fortnight or more the flies 
come out of these pupae. They resemble the ordinary 
house fly, but are considerably smaller. The first flies 
usually appear towards the end of April. There are 
two or three broods a year and the winter season is 
usually passed as pupae in the soil, but also as adult 
flies. From the pupae ichneumon wasps and small rove- 
beetles may be hatched out; these are parasitic and 
help to keep down the number of flies. 
Remedial Measures. 
In America these flies have been successfully kept 
in check by preventing them from laying their eggs in 
the soil near the cabbage roots. This is done by 
means of tarred cards about 3 inches across. They 
