“In the summer, in the College garden, the woolly foxglove, Digitalis lanata, is visited by little bees which become stuporose and lie upside down in the flowers, seeming unable to fly away when disturbed.” –Dr Henry Oakeley, Garden Fellow at the Royal College of Physicians (RCP) Medicinal Garden.
I became fascinated with the idea of ‘poisonous honey’ when I worked at the College. Watching bees foraging on the intoxicating inhabitants of the physicians’ Medicinal Garden, my imagination ran wild with thoughts of insects tempted by sinister sweetness, putrid pollen and foul fruit. What seductively dark nectar would the bees return to the hive to convert into undesirable honey? When I asked Henry, he told me the story of the bees in the woolly foxgloves and he kindly sent two beautiful photographs taken in the College garden.
The colour and flavour of honey comes from the variety of nectar sources visited by the bees. From spring mint and summer blackberry to autumn woods and bitter ivy, the taste and smell of honey can evoke intense reactions, not always good. The strong flavour of privet honey, for example, is described as ‘objectionable’ in Collins Beekeeper’s Bible, while Ted Hooper in A Guide to Bees & Honey confesses: “I cannot say I have ever found much wrong with it”. But whether you like ivy, heather or rapeseed, ‘unpalatable’ honey is a matter of personal taste.
What, then, of honey with truly ‘undesirable’ qualities from the nectar that is gathered, being harmful to bees or humans, or both? In this post, I’m going to look at the possible toxicity of honey from the nectar or pollen of plants rather than artificial contamination.
“Just when you thought that honey was always a wonderful health food,” says Henry, pointing me in the direction of rhododendron – a common culprit of toxic honey that can be harmful to bees and humans. According to Wikipedia, a chemical group of toxins called grayanotoxins found in rhododendrons and other plants of the family Ericaceae may, very rarely, cause a poisonous reaction of ‘honey intoxication’ or ‘rhododendron poisoning’.
Xenophon and his Greek army retreated ill from Persia in 399BC as a result of ‘toxic honey’ and Pompey’s soldiers fell foul of ‘maddening honey’ in the Third Mithridatic War in 65BC. These historical accounts name varieties of rhododendron honey as causing a “feeling of drunkeness, to vomiting and purging, and madness that lasted for days” (Collins). A botanist’s tale of poison honey is given by Frank Kingdon-Ward (1885–1958), during his travels in northern Burma towards Tibet. He recounts symptoms similar to acute alcohol poisoning, suffered along with his travelling companions, after eating honey produced in the rhododendron season. The local Tibetans ate the honey without ill effects (Collins).
Piers Moore Ede vividly describes sipping the ‘wondrous toxic honey’ of rhododendron flowers collected by the honey hunters of Nepal: “It resembled drunkenness at first, but then became visual, like a magic mushroom trip I remembered from university. Painted dots were dripping across my irises like technicolor rain. My body felt light and tingly, filled with warm rushes and heat-bursts. It was wild and strangely wonderful” (Honey and Dust: Travels in search of sweetness).
An incident of poisoning reported in honeybee colonies on Colonsay Island off west-coast Scotland in 1995, referenced in Yates Beekeeping Study Notes (Modules 1, 2 & 3). “The bees had died out completely in 2–3 days after starting to collect nectar from Rhododendron blossoms (Rhododendron thomsonii) caused by the poison andromedotoxin or acetylandromedol.” Ted Hooper writes on the case of Colonsay Island’s bees: “The West of Scotland College of Agriculture Study showed that the poison andromedotoxin was involved”.
It sounds like rhododendrons are not a desirable source of forage for bees! However, to put the risk of honey poisoning from rhododendron, or any other toxic plant, into perspective, I asked John Robertson of The Poison Garden website: “Put simply, something has to go wrong for toxic honey to be produced and then it has to go wrong again for it to cause human poisoning.” OK, so what can go wrong?
“The first thing that has to go wrong is to have a lack of species diversity. Generally, bees visit so many different plants that they don’t get a concentration of any particular toxin. This can go wrong, as in the west of Scotland, where Rhododendrons are almost the only thing in flower early in the spring. But, nectar from Rhododendron is toxic enough to kill the bees so they tend not to return it to the hive. Experienced beekeepers know not to let their bees out at this time of year. I haven’t seen any reports of poisoning from honey made from Rhododendrons.” John writes more on The poison garden blog, entry for Tuesday 27 September 2011.
Both John and Henry brought my attention to honey from the tutu tree (Coriaria arborea) in New Zealand, which could cause harm to humans, but this is due to the unusual way in which the honey is produced by insects. John says:
“Bees collecting nectar directly from the plant do not produce poisonous honey. But, a vine hopper insect also feeds on the nectar of the plant and excretes a sweet ‘honeydew’ containing a high concentration of plant toxins. Especially in times of drought, bees may gather this honeydew rather than nectar from the plants. Because this is a well-known problem, however, there have been no instances of poisoning from commercially produced honey since 1974. When four people were taken ill in 2008, the source was traced to honey produced by an amateur who was not aware of the problem. Another instance of the flaw in the belief that the more ‘natural’ something is the better it is for you.” Read more on The poison garden blog, entry for Thursday 30 June 2011.
Rhododendron is not the only mischievous plant in the garden. Yates lists common ragwort (Senecio jacobaea) in its section on unpalatable honey as “an injurious weed in the Weeds Act 1959, is poisonous to cattle and horses causing damage to the liver with pyrrolizidine alkaloids“. However, bees work the blossom for nectar and pollen with no ill effects to produce a bright yellow honey with an unpleasant smell.
What other mutinous plants, then, produce nectar and pollen that is harmful to the bee?
The innocent-looking buttercup that pops-up in spring has bitter tasting leaves from a toxin called protoanemonin present in the sap. In 1944 in Switzerland, spring dwindling, or ‘May disease’, occurred after bees brought home pollen from the Ranunculaceae family (buttercup): “Nurse bees appeared at hive entrances trembling and unable to fly, excitedly moving on the landing board, losing control of their legs, rotating violently on their backs, becoming paralysed and dying. The leaves of most species of buttercup are poisonous and avoided by livestock” (Yates).
As the reference to this case is old, I dug deeper for something more recent. I found a study in the journal Functional Ecology, published by Wiley-Blackwell, which showed the contradictory effects of buttercup pollen and viper’s bugloss pollen in two closely-related species of mason bees: “While the larvae of Osmia cornuta were able to develop on viper’s bugloss pollen, more than 90% died within days on buttercup pollen. Amazingly, the situation was exactly the opposite with the larvae of Osmia bicornis” (Science Daily press release). The researchers suggested that some flowering plants used chemical defenses to prevent all their pollen being used by the bees to feed their larvae, rather than to pollinate the flower.
In 1951 another account of bee poisoning was reported in Switzerland, this time from the silver fir (Abies alba), which is a source of honeydew toxic to bees. “Thousands of returning foragers, with a waxy black appearance, were reported dying outside hives.” It was thought that sap-sucking insects feeding on the silver fir had converted the plant sap into sugars toxic to the bees (Yates). I was unable to find a more recently reported incident of silver fir honeydew poisoning in bees, although I came across a website that said silver fir honeydew honey is an “excellent table honey that goes well with cheese”. Is Abies alba still foraged for honey? If anyone has further information, I’d be interested to know.
In California, the pretty blossom of the buckeye chestnut tree (Aesculus californica) wickedly beckons bees to feed from its nectar and pollen: “The bees become black and shiny, trembling and paralysed. Non-laying queens, dying brood and infertile eggs have also been reported. As this species covers 14 million acres in North America its effects on honeybees are well known to local beekeepers” (Yates). You can read more about the buckeye chestnut tree and the honeybee in this interesting article by the University of California’s Bug Squad.
Then there is the mountain laurel (Kalmia latifolia), native to eastern US, introduced to Europe as an ornamental plant, and toxic to bees, humans and livestock due to the presence of andromedotoxin which could accumulate in the honey (Yates). However, the honey is reportedly so bitter that it’s unlikely to be eaten and cause poisoning (Wikipedia).
All in all, it seems you’re more likely to come across a ‘poison honey’ in an episode of Poirot than find it on your breakfast table. John comments that the taste and texture of ‘bad’ honey, such as from common ragwort which “is waxy and unpleasant”, is probably enough to prevent anyone from eating too much of it. That, then, puts the lid on a fascinating topic.
With thanks to
A huge thanks to Dr Henry Oakeley and John Robertson for generously sharing their vast knowledge of plant lore for this post. If you’re interested in reading more about poison gardens or exotic plants, check out the links in the reading list below.
EDIT 19.01.15: And if you enjoyed reading my post, thank you. I’ll be making some edits to the information given here in due course in light of further information.
• A tour of the medicinal garden of the Royal College of Physicians by Dr Henry Oakeley, published by RCP
• A year in the Medicinal Garden of the Royal College of Physicians by Dr Henry Oakeley, published by RCP
• Rhododendron yakushimanum ‘Grumpy’ from RCP Medicinal Garden online plant database by Dr Henry Oakeley
• The Poison Garden website posts by John Robertson from Thursday 30 June 2011 and Tuesday 27 September 2011
• Toxic honey entry in Wikipedia
• Collins Beekeeper’s Bible by Philip Et Al Mccabe, published by HarperCollins
• A Guide to Bees & Honey by Ted Hooper MBE, published by Northern Bee Books
• Yates Beekeeping Study Notes (Modules 1, 2 & 3) by JD & BD Yates, published by BBNO | (Yates recommends further details on undesirable nectars can be found in Honey Bee Pests, Predators and Diseases by RA Morse and R Nowogrodski, published by Cornell University)
• Honey and Dust: Travels in search of sweetness by Piers Moore Ede, published by Bloomsbury
• Claudio Sedivy, Andreas Müller, Silvia Dorn. Closely related pollen generalist bees differ in their ability to develop on the same pollen diet: evidence for physiological adaptations to digest pollen. Functional Ecology, 2011; DOI:10.1111/j.1365-2435.2010.01828.x | sourced via Science Daily press release.
• University of California’s post on buckeye chestnut tree and the honeybee from the Bug Squad
• Mad honey poisoning‐related asystole from US National Library of Medicine | National Institutes of Health
• Emily Scott of Adventuresinbeeland’s Blog has written a brilliant post on 1st Honey bee products and forage revision post: a list of floral sources of unpalatable honey;
Further winter studies for bees can be found in my blog index.
Slight discrepancy in the identification of the bee. Anthophora bees are active very early in the year only Furcata the fork tailed flower bee is active in summer. The bee in the image quoted as a Anthophora bee is actually an Anthidium manicatum a summer active bee which collect the hairs of plants to build its nest.
Ah, I had wondered as I read that Anthophora bees have green eyes, although my bee ID skills are limited to honeybees and a few bumbles and solitary bees. I’ll have to look out for Anthidium manicatum next summer.
Very interesting post
Thanks, I had it mind as a plot for a murder mystery novel but decided to blog it instead 😉
you could still write the murder mystery 😉
What a superb piece of writing. I never knew that the poor bees suffered so from bad flowers. As if their lives aren’t already hard enough.
And yes, do please write a murder mystery 🙀
Yes, I thought that too. It seems there are alot of poison perils out there for bees as well as pesticides. Poor bees!
Love this post and especially the role of poisonous honey in history. It makes me rethink my post on ‘bad honey.’ Could that be a reference to poisonous honey? Something to think about…
I was trying to look that up, which of your posts on ‘spoiled honey’ was it? Although I’m no botany expert, The poison garden website http://www.thepoisongarden.co.uk/ and RCP online plant database http://garden.rcplondon.ac.uk/ look like great resources to find out more about exotic plants and their effects.
Emma, if you will permit the links, the posts can be found at https://mylatinnotebook.wordpress.com/2013/10/08/spoiled-honey-made-good/ and https://mylatinnotebook.wordpress.com/2013/10/29/but-can-honey-be-spoiled-more-on-mel-malum/. Thanks for your links, they look interesting. Have you seen the discussion on sugar solution on the BBKA site: about the boiling of sugar solution being poisonous to bees? That’s if they don’t get dysentery from being fed it at the wrong time of year. Rough life these bees lead!
I’ll read those later thanks!
Ah yes, I did read those. I think this sounds like spoiled honey that has fermented or from having the lid left off reabsorbing moisture from the air (hygroscopic).
Yes, I see most of the discussions on BBKA forums – the boiling of sugar solution causing bees to be sick is well known. Best to stir patiently on a low heat when making syrup. Although many beekeepers in London, ourselves included, have fed syrup later this year due to warmer weather. I’ve learned over the years the beekeeping calendar is more guidance and you have to feel the rest of the way from observing the seasons and the bees.
Fascinating! Great post. There are quite a few Rhododendron in the neighborhood but I think there’s enough diversity that time of year that they aren’t any threat to our bees or us. The worst we get is reports of foul smelling honey, probably from the hawthorns that are so numerous in the cemetery up the hill.
Foul smelling honey from hawthorns in the cemetery, my imagination could run wild with that one too. I suppose cemetery plots are a good source of tree-and-flower forage for bees. Yes, I think there must be such a variety of plants in London parks and gardens that, like in your area, bees are unlikely to be affected by a particular plant. In fact, it’s the variety in colour and flavour of honey from different hives at the same apiary that I’m also curious about.
I adore those photos of the rhododendron flowers. Thanks for sharing your winter studies!
Creative Commons is a great resource, as is Wikipedia, although I must remember to take more flower photos next year.
Nice post. I loved the historical references. In some parts of New Zealand honey is tested for turin content before sale, especially during droughts – warm dry weather brings heaps of the tutu vine hoppers, and less available nectar. Manuka honey has its own toxins – but they affect bacteria, not people, so make it an antibiotic/antiseptic.
I guess we’re lucky here not to have those complications with our honey – no tutu trees or vine hoppers! I like the comparison with manuka though, I’ve read research papers on manuka and as an aromatherapist I haven’t noticed a significant difference in using manuka or other types of honey in therapeutic recipes. It’s all a fascinating topic, however – the ‘good’ and ‘bad’ chemistry of the natural world.
Great post!! I knew about rhododendron, but the other poisonous flowers that bees could visit were a surprise to me. And I followed the link to The Poison Garden and that is fascinating!! He mentions the recent story about the alleged poisoning of someone in England that was thought to be due to rubbing against Aconitum. I read this story on line when it happened and was very skeptical as I have touched it often when cutting the flower for arranging. But I had wondered if gathering nectar from Aconitum which I grow a lot of and love would taint the honey. But not to worry, from your post, I gathered that the bees visit so many flowers, it wouldn’t be a problem.
I’m not a plant expert but it seems the risk of poisoned honey from a toxic plant is rare and unlikely. I was more interested in effects on bees as they drink direct from the source. Glad you enjoyed the poison garden blog too, it’s just fascinating!
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Thanks for referencing my post, I’m glad you enjoyed it 🙂
Extraordinary and fascinating, EST. Not something I knew about at all. How interesting that the ancients experienced the toxicity so significantly. I must say the list of symptoms in that para take me back a good few years to undergraduate days… I just thought that was what a normal week felt like. RH
Thanks RH. Historically it sounds like the ancients knew well the effects of poison honey and used it as an early biological warfare. That is, if accounts are taken literally, after all the armies could’ve stopped to drink mead at a rave along the way then claimed to have been poisoned! 😉
Fascinating post, I found myself checking I did not have any dubious plants in my garden. I did notice that my friend Michel was very happy when his neighbour’s privet hedge flowered and he asked him not to cut it as his bees loved the flowers. However, privet is not so common in this area so there would be no risk of it becoming a major source of his bees nectar. Amelia
Privet must be ambrosia to the bees! I haven’t tasted privet honey though what I’ve read suggests it’s a bit like marmite.
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I was asked if winter aconite could be safely planted around a friend’s bee hives in zone 5b. I have been unable to confirm or deny the safety. Could you help me out? Thank you.