Rhododendron ponticum is known as a source of toxic nectar which causes bees to produce ‘mad honey’, used by European armies through the ages as a weapon of war.
Just two to three teaspoons of the spring honey made by Himalayan Giant honey bees (a subspecies of Apis dorsata) can result in temporary paralysis for a day or so, according to Mark Synnott’s article ‘The Last Honey Hunter‘ in National Geographic.
A market for the honey exists because some people believe it improves sexual performance
Which bees visit Rhododenron ponticum?
R. ponticum was introduced to Ireland in the 18th century and has invaded large areas of the countryside, where it is regarded as a pest. Yet research led by Prof. Jane Stout, Professor in Botany and Dr Erin Jo Tiedeken, Research Fellow at Trinity College Dublin, has found that its flowers are visited almost exclusively by bumblebees, with occasional visits from solitary bees, flies, ants and wasps.
Professor Stout and Dr Tiedeken found that the nectar’s grayanotoxins cause palpitations, paralysis and death within hours – for honey bees.
They also tested the grayanotoxins on an Irish species of mining bee, Andrena scotica; this species did not suffer increased mortality but had its behaviour severely affected, for example becoming paralysed or spending increased time grooming.
In contrast the nectar has no apparent effect on worker buff-tailed bumblebees. Professor Stout suspects that the subspecies of honey bee that makes mad honey in the rhododendron’s native range has probably evolved to resist the toxins in a similar way to the bumblebees.
Rhododendrons are an excellent source of food for bumblebees. “They do provide floral resources in areas where perhaps there might not be very much,” Professor Phil Stevenson, Royal Botanic Gardens at Kew.
The researchers suggest that within their invasive range (as studied in Ireland) the plants “reduce or stop entirely the production of nectar toxins to ensure sufficient pollination success (Egan et al., 2016)“. That makes sense – it’s in the best interests of the plants to attract pollinators.
Should beekeepers worry?
Rhododendrons are unlikely to cause British beekeepers many problems. Research carried out by Professor Stout and Dr Tiedeken suggests that honey bees will probably avoid R. ponticum. Others rhododendron are likely to be less toxic too.
Rhododendrons may only be a problem for beekeepers surrounded by large areas of R. ponticum, which could smother out other plants and reduce the amount of forage available for honey bees.
See more:
- Grayanotoxin Poisoning: ‘Mad Honey Disease’ and Beyond
A scientific paper on mad honey. Contains a fascinating description from the Greek warrior-writer Xenophon in 401 BC on the effects of the honey on an army – “those who had eaten a great deal seemed like crazy, or even, in some cases, dying men”. - Mad honey
A 2018 post by Scottish beekeeper & scientist The Apiarist, who has a particular interest in rhododendrons because he’s surrounded by them. - Hallucinogen Honey Hunters documentary
A tribe in Nepal hunt wild rhododendron honey with natural psychoactive properties. One falls unconscious after overdosing on the honey. - The strange history of ‘Mad Honey’
Emma Bryce writes about Turkey’s hallucinogenic rhododendron honey (deli bal), produced on remote mountainsides smothered with vast fields of cream and magenta rhododendron flowers. - ‘The Last Honey Hunter‘ by Mark Synnott (National Geographic, July 2017, p.80-97)
Stunning photos of 57 year old Mauli Dhan harvesting ‘mad honey’ from steep Nepalese cliffs. Mauli climbs for the honey since a spiritual dream many years ago set him on his path. In his people’s tradition it is bad luck for anyone who has not had this dream to take the honey. - ‘Poisons in rhododendron nectar‘
Philip Stevenson (Plant Chemist) and Alison Scott-Brown (Plant/Insect Ecologist) from Kew’s Natural Capital and Plant Health department report on the toxicity of natural chemicals in the nectar and leaves of Rhododendron.
