i, 
method could be found so effectually to stop their 
ravages as the employing women and children to 
pick them off, either by the day, or at three halfpence 
the pint. I have taken great pains to find out the 
fly which produceth them, but to little purpose. 
Albin has figured the caterpillar well, and says, 
“ These black caterpillars, of the Ichneumon kind, 
were found feeding on the turnip-leaves in the be- 
ginning of September 1719, they being so numerous 
at that time about London, that they destroyed 
whole fields of them: about the latter end of Sep- 
tember they went into the earth, and spun them- 
selves up in a transparent case, and changed into a 
chrysalis, and in May following came forth a small 
Ichneumon fly, as in the figure annexed *.” 
Now the figure of this fly is not of the Ichneumon 
kind; it has only two wings, and belongs to the 
genus AZusca ; but none of that genus spring from 
caterpillars, but from maggots. I have offered and 
given premiums to many persons to pick up and 
bring me all the different sorts of flies which they 
find upon the turnips, but can gain no satisfactory 
knowledge about them; they have all, or most of 
them, brought me a species of fly with four wings, 
with black and yellow intermixed upon their bodies 
and legs, which have been prodigiously numerous ; 
but I know not what it is, unless it be the Zen- 
thredo Rose. I have inclosed you two specimens, 
and beg you would get me the best information 
you can about it, and at the same time to find out, 
* Albin’s History of English Insects, tab. 62. 
