Before I became a beekeeper, I can’t remember ever learning about extra-floral nectaries. No-one goes to an extra-floral nectary show, or walks down the aisle clutching a bouquet of exquisite extra-floral nectaries. The world goes by without most of us ever thinking about them. Yet they are very useful to insects such as ants and bees.
So what the heck is a extra-floral nectary anyway? Well, it’s a patch of glandular tissue which secretes sugar but is not part of the plant’s flower, which is why it’s ‘extra-floral’, i.e. not floral. These glands have been observed in at least 2000 different species of plants, including broad bean, cherry, cherry laurel and plum. Below is a picture I drew showing where they are located on these four examples.
Since these nectaries aren’t near the sex parts of a flower, they obviously have no connection with pollination. So what are they for?
There are a couple of different theories about the function of extra-floral nectaries. One is that the nectaries may act as ‘sap valves’ to regulate sap pressure within the plant. The thought is that if the sap in the phloem tubes (which transport sap around the plant) become too concentrated with nutrients, the plant releases nectar from its extra floral nectaries to reduce osmotic pressure.
Another theory, which seems to be more commonly accepted, is that the nectaries are a defensive mechanism to reward ants, which will then stop other animals from eating the plant. In The Honey Bee Around and About, Celia Davis mentions an experiment which found that when broad beans had a proportion of their leaves removed to simulate damage by herbivores, the plant produced a lot more extra-floral nectaries within one week.
Extra-floral nectaries: the unobtrusive, unshowy nectar pools of the insect world.
References:
Books
- Beekeeping study notes (Modules 1, 2 & 3), J.D. & B.D. Yates (2013)
- The Honey Bee Around and About, Celia F.Davis (2009)
Websites
- Extrafloralnectaries.org – lists thousands of plants worldwide with extra-floral nectaries
- Module 2 study notes, Mid Bucks Beekeepers Association (2012)
- The secret of extrafloral nectaries, Rusty Burlew, HoneyBeeSuite.com (2016)
Adventuresinbeeland's Blog 
Thank you for another fascinating insight into the insect world Emily.The many varieties of Prunus seem to be particularly bountiful to the Bees, and I was particularly interested in the Cherry Laurel Prunus Laurocerasus, because I had always thought that bees were gathering products for Propolis from this plant as well as from Poplar ,Horse Chestnut etc. The bees certainly run up and down the veins on Laurel leaves.
Balsam and Busy Lizzies also have very visible sugar lumps on extrafloral nectaries.
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Thanks Jonathan. Fascinating that you’ve actually seen sugar lumps on the balsam and busy lizzies, shows what a great source of fuel they are for insects.
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Thank you very much Emily for sharing and I really like your drawings they add well to what you describe. I wish we had modules like you have in this country. From you I get to learn at 2nd hand. Would you like to know about the bee hives I have designed?
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I would love to hear about the bee hives 🙂
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Thiis is all new to me Emily, I hope you get to read it. The bee hives have 22 combs in one space. So you do not have a brood box with a separate honey box. There are no excluders for the queen. She can go where she likes. In a natural setting the bees do not mix up their pattersn. This hive hopes to let the bees live as natural as possible in a man-made habitat. They have to make their own wax combs right from the beginning. No other assistance is given other than a triangular wooden lathe on the top and one side to encourage them to build from. I have perspex windows on the top and two sides so that the bees can be observed without opening the roof. Eventually we hope to provide an educational aspect to where our bee sanctuary is located. The windows will allow people to see but the bees will have no bother I hope from the spectators. Hopefully the long window on the back side will allow me to see if the bees are building queen cells. I should then be able to monitor the swarming date and be ready with my skep to catch them in time.
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Thanks Lindy, it sounds intriguing and great that you’ll be able to show people the bees easily. Are the windows covered most of the time so that the bees are usually in the dark? I think they would prefer not to have sunshine going in all the time.
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The perspex is flush with the inside wall of the hive, the bee space between the wall and first hanging comb should, if all is well, not become joined with wax by the bees. In the aperture between perspex and wooden outside there are exactly fitting insulated blocks. These fall into their space and are kept there by turning little metal handles. Most times these doors are in place. Only when you want to show someone what is happening inside do you remove the wooden door. The perspex sees to it that the temperature does not change within the hive. Hope this answers your query Emily
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Sounds very fancy! I am impressed.
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Thank you Emily, I had no idea that these existed.
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Me neither before entering the world of bees!
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Fascinating! Are ants the only insects that collect sap from extra-floral nectaries? Or will bees work them, too? Do they produce sap all year?
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Other insects, including honey bees and bumbles, will collect the nectar too. There’s a nice photo here of a bumble on a bean e-f-n: http://s19.photobucket.com/user/WaterAid/media/Beans/bbee_extrafloral2.jpg.html
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I have often watched the bees working the Laurel leaves but did not know about the extrafloral nectaries on them.,
Busy Lizzies (Impatiens walleriana) have tiny sugar lumps on stalks behind the flowers and also fascinating spring loaded seed pods which explode when touched….,which I delight in demonstrating to my grandchildren!!
You have taught others so much by sharing your study drawings and comments and I wish you every success in your Saturday Exam . Well done and thank you..
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Plants are amazing! Thank you Jonathan.
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I’ve seen these and I never knew what they were! So if I understand correctly bees could be gathering nectar from these? Fascinating! Amelia
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You are observant to have spotted them! Yes, bees do visit them, although flowers are visited more often. There’s a good photo here of a bee on a e-f-n: http://s19.photobucket.com/user/WaterAid/media/Beans/bbee_extrafloral2.jpg.html
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Those are interesting photographs. I’ve never noticed the bees anywhere but on the flowers of my broad beans. That is a challenge for next year for me!
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He he!
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This is really interesting and I never heard of nectaries. I like your drawings showing them on different leaves, plus the reasoning on the ant reward. Fun to learn new things.
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Hallo Emily, two things…. Rusty Burlew of Honeybeesuite.com posted a text tonight regarding extra floral nectaries. It reminded me that you had told us such interesting things about them during your exam times and I remembered the drawings. I mailed this part of your blog to Rusty with your drawings because I thought she might enjoy them as I did.
2nd thing, baby, do you care to drink tea with ginger in it. It should calm your nausea. Also have you considered whether you might have a lack of magnesium. Often a woman has a lack of this mineral during pregnancy and again later at time of menopause. It wouldn’t hurt to check I think Emily and it can be of great help in carrying a child healthily right through. In this country it is very often prescribed for mothers to be, I don’t know if it is in England. P.S. You mustn’t add this one to your blog its just from me to you, Goodnight and God Bless Emily
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Hi LindyLou, thanks for your comment, I’m happy to have it on my blog if you don’t mind? If you’d rather it was deleted let me know. Thanks for remembering my post and emailing Rusty, I read her website and really like it. Will look into the lack of magnesium, I’ve not heard of it being prescribed here but I can try to eat more bananas and yogurt together, from reading online it sounds like that should help 🙂
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Rusty wrote back to me Emily, Emily’s drawings are great. I’m always jealous of those who can draw. Plus her site is a wealth of information. You know I do love being a beekeeper with internet access, it has opened up a gigantic world of knowledge and internet companions who all share a love of bees.
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That is so nice of her!
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