76 
HOP-FLY. 
this it will appear that, in duty alone, a little, insignificant 
looking fly has control over 450,000/. annual income to 
the British Treasury ; and supposing the hop-grounds of 
England capable of paying this duty annually, which they 
certainly are, it is very manifest, that in 1 825, these crea- 
tures were the means of robbing the Treasury of 426,000/. 
This seems a large sum, but it is not one-twentieth part of 
the sums gained and lost by dealers during the two years 
in question. 
The hop-fly makes its first appearance generally about 
the 12th of May, sometimes two days earlier, but almost 
invariably between the 10th and the 30th ; and it is worth 
noticing, that it usually appears on the same day in the 
four districts of Kent, Sussex, Farnham, and Worcester. 
It always makes its first appearance in the winged state, a 
solitary fly being found settled very quietly here and there 
under the young leaves. If the weather is warm, with 
mild, kind rains during the last twenty days of May, these 
flies begin to produce young ones, which are very small, 
and are called deposit, or knits. These grow very fast, 
and in a few days become green lice, which is merely a 
larger form of the same animal. These lice very soon be- 
gin to breed, and so keep on, knits and lice, knits and lice 
only, to so great an extent as to destroy the plant, when 
they appear to die with it. I have never found that the 
deposit of the hop -fly leaves the plant at all, or ever be- 
comes a fly while there : in this respect diflering from the 
Aphis of the rose, guelder-rose, bean, &c., of which I have 
spoken above. Frequently, when the weather in May has 
been dry, and cold, and windy, the fly has been known 
to leave the plant, and entirely disappear, even after re- 
maining several days ; yet whilst it tarried showing very 
