Inside: A look at a rare but well-documented type of honey poisoning that comes from the nectar of rhododendron flowers.
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A recent trio of foodborne poisonings
An article in today’s Seattle Times (2011) reports that three King County residents fell victim to food-borne toxins. Unfortunately, one came from a sample of local honey.
According to the article, a man became ill after eating a portion of honey he had purchased at a local farmer’s market. He reported vomiting and “intestinal difficulties” which began about an hour after consuming the honey. Doctors sent the honey sample to the state Department of Agriculture, but tests could not confirm a toxin.
However, the man’s symptoms led officials to believe the honey contained grayanotoxin, a material found in rhododendron nectar. The condition, also known as “rhododendron poisoning” or “honey intoxication,” is well-documented but rare.
Grayanotoxin in rhododendron nectar
Grayanotoxin is a naturally-occurring neurotoxin found in the nectar of rhododendrons. According to Wikipedia, symptoms include salivation, perspiration, vomiting, dizziness, and low blood pressure. The condition is rarely fatal and usually abates within 24 hours.
In a cruel hit to small honey producers, the author of the Seattle Times piece writes that local honey is much more likely to contain toxic levels of grayanotoxin than honey coming from large commercial producers because commercial producers mix honeys from many sources—a variation on “dilution is the solution to pollution.”
The ABC & XYZ of Bee Culture mentions that both the nectar and pollen of rhododendron are poisonous to bees as well as humans. Although the toxin can kill bees, it is well diluted with water in the nectar. But as the water is driven from the nectar to produce honey, the grayanotoxin concentrates to poisonous levels.
Honey poisoning is extremely rare
I didn’t find any references to how frequently honey intoxication occurs but the numbers must be low. The Puget Sound area teems with rhododendrons—in fact, it is the Washington state flower—but few cases of poisoning get reported.
My own property has many hives of bees and many rhododendrons but I have never seen a honey bee on a rhododendron flower. These observations lead me to believe that rhododendron is not a preferred forage for honey bees and they probably collect it only in rare circumstances when other more favorable blooms are not available.
Other food-borne toxins in local news
If you want to know more about food-borne toxins, the Seattle Times article is interesting. Besides honey intoxication, you can read about toxic squash syndrome and scombroid fish poisoning. So, what’s for dinner?
Rusty
Honey Bee Suite
OK —- related to this, the Slow Foods Ark of Taste includes Italian rhododendron honey. I have friends who brag about eating this and my reaction has always been “omg poison!” So, are their rhododendrons different? Or is the standard for poisoning not so high in heirloom foods? I have been trying to figure this out for like, six months so I’m really glad you wrote about this.
Jess,
Wikipedia says, “Honey from Japan, Brazil, United States, Nepal, and British Columbia is most likely to be contaminated with grayanotoxins, although very rarely to toxic levels.” Also, The ABC & XYZ of Bee Culture says that there are several species and hybrids of rhododendron, including R. ponticum, that produce the toxin. So it looks like just certain species are bad and those species don’t seem to have come from Italy.
The bees must be able to tell the difference, at least most of the time. Interesting. I’d like to try Italian rhododendron honey.
Here in the Bellingham area of northwestern WA we have lots of beautiful rhododendron in our neighborhood. Bees love them! I have personally seen honey bees, bumblebees and other smaller bees, as well as other flying insects (but not butterflies) collecting nectar and pollen from the large deep pink rhodie bushes flanking our driveway!
Joyce,
I have lots of rhododendrons as well, but I’ve never seen a single honey bee on them. However, the bumbles love them, as do many of the larger ground-dwelling bees and even some of the masons. Solitary wasps seem to like them too.
Hallo Rusty, I could do with some advice from you. Last Saturday was the national Bio-dynamic beekeeper day in The Netherlands, a real red letter day so to speak. In the foyer van de school where the event takes place there are people who have products and plants to sell specifically of interest to beekeepers. I bought 3 Aesculus Californica young trees. €10,00 per tree.
When I got home late that night I looked up in Wkipedia information about my trees. I was dumbfounded to read that the nectar and the pollen of these Calfornian Chesnut trees are fatally poisonous to European and Asian honey bees. I contacted the grower on the monday morning and he in turn was quite shocked. He reimbursed me half the money and told me to destroy the trees. His nursery is too far away for me to take them back and he didn’t want to drive half way either…
I feel bad about throwing these, otherwise healthy, trees in the bin but all my friends are bee keepers too so they won’t appreciate such a ‘present’. As well as this aspect of the problem, most legislative councils are pro active in having useful bee forage plants in public areas these days so I don’t know what to do and would appreciate some input from you. My terrain is 1ha or approx 2 acres if I include the piece we hope to buy in the future. Would my bees avoid it if there was plenty of other forage available or is the risk too great? Thanks for your thoughts anyone else too.
Lindy,
Wow, that is unreal. Apparently, honey bees go nuts over the flowers which produce lots of nectar and pollen, but reports of poisoning seem to occur in dry years more than in wet ones. The old adage, “Dilution is the solution to pollution” seems to be at play here. In other words, if the colony has plenty of food sources, the amount of poison coming into the colony is diluted by all the good stuff. On the other hand, in dry years when these trees are more productive than other sources, there can be significant brood damage. This UC Davis article explains it well.
If it were me, I think I’d give the trees to someone without honey bees. Having them so close to home would be something to worry about every year, and there is enough to worry about the way it is.
I was hoping to add a hive to my property which borders a forest that has a mixture of trees, maple, birch, fir, pine and cottonwood among others. It also has a few rhododendrons and blackberries in the area. The native honey bees have vanished over the last few years. Would this mix of foliage be harmful to the bees or their honey?
Thank you for your help!
Fred,
That sounds like a pretty standard complement of foliage. Honey bees don’t like rhododendron, so unless there is nothing else around, they stay clear of it. I have rhododendrons all around my hives, and I don’t think I’ve ever since a honey bee on it.
I love your work – approachable, informative, and always rigorously accurate. I have never noticed a spelling or grammatical error before, but I believe the word you wanted was “teems”.
Bill,
Thanks! How embarrassing.
I suspect that if/when honeybees visit a rhododendron, they die from their own nectar consumption without taking any home to the hive to be mixed with the other nectars and made into honey. Research shows that bumble bees can tolerate the toxin but honeybees die when exposed to it.
https://www.kew.org/read-and-watch/hidden-poison-rhododendron-nectar
LizzyBee,
I agree about bumble bees and I see them on rhododendrons all the time. Also, Andrena mining bees seem to like it. But how do we get occasional cases of honey intoxication if honey bees didn’t live long enough to transport it back to their hive?
Rusty,
Here in the midwest we are dealing with “poison hemlock” which has been termed the most poisonous plant in America and is spreading like wildfire. It is a relative of Queen Anne’s Lace, with many white flower clusters. Any research into bees creating poisonous honey from visiting these plants. It’s scary enough to make me quit selling at farmers markets.
Dwight,
According to the US National Park Service, poison hemlock (Conium maculatum) is found in all but four US states: Alaska, Florida, Hawaii and Mississippi. It especially loves wet or swampy areas, which is why I have huge swaths of it near my home. My apiary sits within yards of big patches of it and has for over 20 years.
Even though 46 states and most of the Canadian provinces have thousands of acres of this stuff, I’ve never heard of a case of honey poisoning because of it. Having watched it bloom for many seasons, I can’t say I’ve ever seen a bee on it. Actually, I don’t see any pollinators on it, which leads me to believe it’s not producing nectar.
I fully realize this isn’t proof, but I think if it were a problem, we would have heard something by now. The one issue that bothers me is it’s in the carrot family, and I know carrot plants produce a honey crop (horrible stuff). It’s also related to queen anne’s lace, which attracts a fair number of pollinators (because of the pollen, I think).
I can’t tell you what to do. I can only tell you that 1) I’ve never heard of poison hemlock honey, 2) I’ve never seen honey bees on the flowers, and 3) I’ve never had personal issues with hemlock honey even though it grows adjacent to my apiary.
If anyone out there has any knowledge on this scary plant, please write.
My taxonomic skills are notoriously suspect, but I googled up your poison hemlock and it looks like a plant we have all around. With no trouble.
However, I’m just here to say I’ve had honey that claimed to be carrot, and it was perfectly fine, if not something I’d go out of my way to buy again.
Roberta,
A few years ago I was visiting a friend in Oregon. I had to drive through miles and miles of fields of carrots that were being grown for seed, and several growers were selling carrot honey by the roadside. So I bought some. Until then, I never met a jar of honey I didn’t like, but that stuff was inedible.