Following up on the structure and function of the mouthparts, this week’s blog features the marvellous mandibles. All the best for everyone sitting beekeeping exams tomorrow.
In common with lots of other animals, we humans have one continuous moveable mandible or lower jaw which holds our bottom teeth in position. and helps us to bite and chew food. Our top set of teeth is embedded in our maxilla which is our immobile top jaw. Honey bees have two moveable lower jaws known as mandibles that swing in and out like the doors of a lift, unlike our jaw which moves up and down to connect with our maxilla. Powerful honey bee abductor muscles draw apart the mandibles, and equally powerful adductor muscles pull them together again1. When not in use, honey bee mandibles fold away in front of the labrum where they are barely noticed. Some of the hairs covering mandibles are involved with the sensory system and enable the bee to register contact between the two mandibles and other surfaces that they come in contact with.
Although the mandibles of queen, worker and drone differ slightly, their inner surfaces are essentially similarly shaped like a spatula, or the small scoop for eating ice cream at the cinema. They all use their mandibles for stabilising their proboscises, but the other uses are determined by the roles the bee plays within the colony.
Let’s look at the functions and the differences between the colony member’s mandibles.
The worker mandible has a set of channels in the depression of the spatulate inner surface which enables brood food, transported from the hypopharyngeal and mandibular glands, to run out into the cells when the nurse bee feeds larvae.
Have you ever had the hairs on your arm tweaked by a bee? It is a strange sensation but demonstrates another use of mandibles in defence and housekeeping work. Hair pulling goes on in colonies along with other defensive behaviour. You might see a dead bee being dragged out of the hive. If you look closely, you will notice the worker grasping it with its mandibles. I’ve seen drones being hauled out by their legs. Guard bees can release mandibular gland alarm pheromone to attract other nestmates to help them repel robbers, and they may use their mandibles in the fight as they grapple with the enemy.
The mandibular alarm pheromone 2-heptanone has been discovered to have anaesthetic properties enabling some invaders to be temporarily immobilised and evicted by honey bees. 2-heptanone acts like the local anaesthetic given before you have that cut stitched up by the nurse. A honey bee can pierce a wax moth larva and anaesthetise it for just long enough to be able to grasp it with her mandibles and remove it from the hive.
Mandibles are needed for nest building and the construction of wax cells, and wax flakes are manipulated and kneaded by the forelegs and mandibles together till they are pliable enough for moving into position for cell making or capping.
Outside in the field, honey bees use their mandibles to bite off sticky resin from plants to make propolis. Mandibles are not used in the field to manipulate pollen grains but back home inside the hive they are. When pollen is needed and taken from a cell, the worker uses her mandibles to move it.
Have you noticed how easily bees chew things up and remove them from the hive? Newspaper from uniting two colonies is the most obvious and you often see piles of finely shredded paper on the floor only hours after uniting two colonies. Bees will chew almost anything that you leave behind in the hive so best keep your notes below the roof well protected!
The queen’s mandibles are similar in size to those of the worker but the surfaces that come together at the front have a jagged projection like a pick. If you’ve ever examined closely a queen cell you will know that it has tougher layers of wax and larval cocoon casings than a worker cell. This requires hard physical work for the queen to enable her to emerge from her cell, and she uses her sharp mandibles like a saw to neatly cut a round exit hole. You may have seen how the round cover often remains attached and sometimes it closes over trapping a worker inside. If you ever find a queen cell that is still sealed long after day 16, when she should have emerged, check it out by opening the end and you might find a worker inside that has gone to clean up the remains of the royal jelly and been imprisoned with fatal results.
Have you ever wondered how it can be that a newly emerged queen can go round and sting her rivals through their protective wax armour plating? It’s simple; she uses her sharp mandibular tools to pierce an opening in the side of the cell before inserting her sting for the fatal blow.
During a flight with a rival queen in the hive, a queen uses her mandibles to grasp her opponent. She steadies her in a firm grip as and curves her abdomen round lining up her sting to deliver the final assault.
Although the queen has well developed mandibular glands, she has no groove running from these glands to the inner mandibular surface because she is not involved with feeding duties.
The drone mandibles are smaller and narrower than queen or worker jaws and are used primarily for stabilising his proboscis. The drone has no need for developed mandibles given his role which is limited to mating and passing on genes. There are small toothlike projections at the apex of each mandible but these are not used for hacking a way out of their cells because mostly drones are helped by their sisters during that final stage. Their mandibles have a good covering of plumose hair though there are fewer sensory hairs. Drones have small mandibular glands which produce a pheromone during the first nine days of adult life. Apparently it is stored and used during mating to attract other drones and, perhaps the queen,by marking the drone congregation areas 2 but the details remains unclear.
1 Goodman, L., (2003) Form and Function in the Honey Bee, IBRA, Cardiff.
Stell, I., ((2012) Understanding Bee Anatomy, The Catford Press.
2 Winston, M.L., (1987) The Biology of the Honey Bee, Harvard University Press.
Supporting Ukraine Through Bees.
This week I found a way to directly help the women and children fleeing the war against humanity in Ukraine. Our bees produced a bumper crop of honey last year and I’m about to sell a colony so I’ve just sent money by bank transfer to a close friend whose mother lives in Poland not far from the border with Ukraine. Karolina’s mother Ola will go out and buy whatever is needed for the people sheltering in her town. She will provide food and pharmacy goods which will bring a little comfort to their lives for now. Thank you Karolina and Ola for helping me help Ukraine.
In 2013 two of my beekeeping friends and I had a memorable adventure in Ukraine when we attended Apimondia in Kiev. I didn’t take a camera because sometimes I just want to be lost in the moment enjoying what I’m seeing without the need to record everything. I’m sorry now that I can’t share images of the most beautiful churches and other buildings with you, but here is my favourite photo of a honey market showing bright yellow sunflower, and brown buckwheat honey. Both are delicious and I bought little chunks hacked off the blocks and bagged. Both these pictures were taken by Cynthia May.
Waiting to register for Apimonida was unforgettable because it took a long time; many hours. We were in long snaking queues outside the conference centre and the weather threw suprises at us. We had sunny spells separated by rain and sleat showers but it was a good time because we made friends with people all round us and we kept meeting them again throughout the week. Local beekeeper Genardy lent me his umbrella when the rain came, and Cynthia, Helen and I huddled gratefully below it for some shelter. We met the late Norman Walsh and family and I forged a friendship with Norman whom I was to meet again several times over the years at beekeeping events in Ireland. When Norman stopped teaching he sent me all his lectures on pen drives which I keep safely in a biscuit tin and refer to from time to time.
Like everyone else in the civilised world, I think about what is going on today in Ukraine and hope for a end to this soon for the sake of the brave and kind Ukrainian people, and the Russians who do not want this war either.