A post by pbh4 in 2012 tells the story, and though the Howes book was first published in 1945 it remains an essential beekeeping tool. Abebooks.co.uk
have copies starting at £4.99 delivered. It was so good that William Kirk absorbed most of it into his
Plants for Bees in 2012, which is well worth the £35.
From F.N. Howes Plants and Beekeeping http://archive.org/details/plantsandbeekeep031830mbp
BUTTERCUP Ranunculus spp.: Ranunculaceae
The numerous buttercups so prevalent in pastures are of little as bee plants. The flowers of many species seem never consequence to be visited by honey bees at all but those of others, e.g. the lesser celandine (R.ficaria) and bulbous buttercup (R.bulbosus) both common species, may be worked for pollen on occasions.
Buttercups are, in general, unpalatable plants, owing to the presence of an acrid poisonous principle, and have caused poisoning in livestock. It is of interest, therefore, to note that in recent years the pollen of buttercups has been proved to be actually injurious to bees in Switzerland and elsewhere in Europe and responsible for a form of 'May sickness'. Bad outbreaks of this malady have occurred in seasons when cold weather has retarded the flowering of the usual early pollen plants, like cherries and dandelions, but not the more hardy buttercups, causing the bees amounts of buttercup pollen.
In Britain there is usually an abundance of other 'wholesome' to collect larger pollen plants in flower at the times so presumably this when form of bee malady buttercups are in bloom, may be less likely to occur. The harmful nature of buttercup pollen, or at any rale that of of Ranunculus, may be the reason why the flowers are species so often completely neglected by hive bees. Their instinct warns some them to leave the flowers alone. (Bee World, 1942, 47, 78.)
