I have just been reading the most delightful book
'Sweet Thames Run Softly' by Robert Gibbings first published in 1940.
It's an account of his journey down the Thames in a punt in 1939 armed with a
sketchpad and microscope.
It's within these beautifully written pages that I found this little gem regarding
how leeches are used to foretell the weather...
" Mr Taylor writing in 1813 suggests that we should put a leech into a large phial
three parts full of rainwater, regularly change thrice a week and let it stand on a window frame fronting the north. In fair and frosty weather it will be motionless and rolled onto a spiral at the bottom of the glass; but prior to rain or snow it will creep to the top where, if the rain be heavy, and of some continuance,it will remain some considerable time; if trifling it will descend.
Should the rain or snow be accompanied with the wind, it will dart about its habitation with amazing celerity and seldom ceases until it begins to blow hard. If a storm of thunder or lightning be approaching, it will become exceedingly agitated and express its feelings in violent convulsive starts at the top of the glass."
So I have a suggestion to the Met Office that they purchase some leeches and try this method of weather forecasting, it sounds that it would be more accurate than theirs!