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APPENDIX. 
APPENDIX B. 
Account of the Black Canker Caterpillar, which destroys the 
Turnips in No? folk. By William Marshall, Esq. Pub- 
lished in the 'Philosophical Transactions' of the Royal 
Society for 1783. Vol. LXXTII. p. 217. 
Among the numerous enemies to which turnips are liable, 
none have proved more fatal here than the black canker, a spe- 
cies of caterpillar, which in some years have been so numerous 
as to cut off the farmer's hopes in a few days. In other years, 
however, the damage has been little, and in others nothing. 
About twenty years ago the whole country was nearly stripped, 
and this year it has been subjected to a similar fate. Many 
thousands of acres, upon which a fairer prospect for a crop of 
turnips has not been seen for many years, have been ploughed 
up ; and as from the season being now far spent, little profit 
can be expected from a second sowing. The loss of the farmers 
individually will be very considerable, and to the country im- 
mense. 
It was observed in the canker-year above mentioned, that 
prior to the appearance of the caterpillar, great numbers of yel- 
low flies were seen busy among the turnip-plants ; and it was 
then suspected that the canker was the caterpillar-state of the 
yellow fly ; and since that time it has been remarked, that can- 
kers have regularly followed the appearance of these flies. 
From their more frequently appearing on the sea-coast, and 
from the vast quantities which have, I believe, at different times 
