Maybe this was all a big mistake. Each time I research bee tongues, I find a cursory review, perhaps two or three paragraphs making the structures sound plain and spartan. So I set out to learn more, an unfortunate choice. I should have known there was a reason everyone avoids the subject.
If you look in a mirror and examine your tongue, it looks simple enough. It’s front and center, all of a piece, and just long enough to fit.
The same is not true for bee tongues. On the contrary, they are intensely complicated, having multiple moving parts with names no one can remember. And the parts have subparts, as do the subparts. But bee tongues are vitally important, especially to bees, so it’s worth thinking about them occasionally.
As I read more and more, I decided to cover less and less in this article. You could make a lifetime study of bee tongues if you wanted to — but I trust you don’t — so this will be a summary.
The long and short of it
No doubt, you’ve heard of long-tongued bees and short-tongued bees. They forage on different plants and collect nectar using slightly different methods. But it turns out that their tongues are structurally different, and the actual length of the tongue has little to do with anything.
Worldwide, there are seven families of bees. Of those seven, just two are long-tongued: the Apidae and the Megachilidae. Since honey bees are in the Apidae, they are by definition long-tongued bees.
The long-tongued bees have a stunning range of tongue lengths, from relatively short, like honey bees, to inexplicably long, like orchid bees. The specialist bees, those that forage on particular plants or plant families, generally have tongues designed to fit their favorite plants. Generalist bees, those that forage on a wide range of plants and plant families, have all-purpose tongues that work in many situations.
The five-part proboscis
In long-tongued bees, the proboscis — the thing we usually call the tongue — is supple and hairy. But more to the point, it’s made of multiple parts, only one of which is the true tongue. The other parts offer structural support — a scaffolding of sorts to protect the real thing.
The true tongue, a flexible central tube, is called the glossa or the salivary canal. The glossa has some internal support of its own, a type of flexible rod running end to end. It also has a groove that runs the entire length.
At the tip of the glossa is a small structure called the labellum. This appendage is crazy hairy on the top side and shaped like a tiny bowl. The bee uses the labellum to lap up refreshment and the hairs keep the food from sloshing out of the bowl.1
Four other parts, two labial palpi and two galeae, come together to form a sturdy sheath around the glossa. The labial palpi and galeae fit together with Lego-like precision, forming a watertight cylinder. This outer tube, known as the food canal, securely protects the inner salivary tube. So, yes, the proboscis is made from a one-part tube inside a four-part tube — at least in the long-tongued bees.2
Help from the mandibles
To keep the proboscis from swaying from side to side as the bee eats, the mandibles extend forward from each side of the bee’s face and brace the entire structure.
Mandibles serve all kinds of functions in a bee’s life, but stabilizing the proboscis is not one we normally consider. Despite that, stabilization is the one function that’s common to nearly all bees. The other uses vary, depending on the species. Females use mandibles for chewing, cutting nesting materials, collecting mud, shaping wax, or removing debris. Males may use them for fighting or mating.3
Regardless of their use, bee mandibles are powerful. They are activated by a pair of oversize muscles that pull them in and out, taking up much of the space inside a bee’s head.
All the subparts
Most references stop here, but this simple explanation doesn’t quite cover the complexity of all the mechanical connections. What I’ve missed in prior discussions is the relationship between the maxilla and the labrum to the proboscis.
In bees, the maxillae (one on each side of the mouth) and the labrum (an upper lip of sorts) fuse to form — deep breath — a labiomaxillary complex.4 You didn’t need to know that, right?
But it’s cool. The labium is in the center and includes both the labial palpi and the glossa. It also includes a bunch of fiddly little parts leading to the glossa called the submentum, mentum, and prementum. The maxillae are on either side of the central labium and include the cardines (stabilizing rods), stipes, maxillary palpi, and the galeae. In all, the labiomaxillary complex comprises 17 moveable parts.
You don’t need to memorize the details, but it’s good to recognize that a bee tongue is not a simple thing. In summary, the proboscis is derived from parts of the maxillae and parts of the labrum, all fused into one extremely intricate structure designed for collecting liquids such as honey, nectar, and water.
The sucking pump
At the base of the glossa is a series of specialized muscles surrounding an empty cavity. This structure, called the cibarium or sucking pump, siphons food from the tip of the glossa through the length of the food canal. Just as pumping your smoker sucks air into the firebox, pumping the cibarial chamber sucks liquid into the bee’s mouth.
Liquid food or water begins its journey through the narrow food canal by capillary action. As it begins to move upward, it’s aided by the action of the pump and by rapid back-and-forth oscillations of the glossa itself.5
To eat, the bee immerses her tongue in the food and spits saliva down through the center of the glossa. At the same time, she sucks food through the food canal. It’s a two-way process — the spit goes down while the food goes up. In a way, it’s like eating a lollypop — you spit as you go. By the time the food hits the bee’s mouth, it is already partially digested.
Packing it away
The ongoing problem is one of storage and convenience. The stabilizing structure formed by the labial palpi and galeae cannot be easily retracted and stashed away. So it must be dismantled whenever the bee is not using it and reconstructed whenever it’s needed. Each of the parts is folded into a Z-shape and warehoused in a compartment called the proboscidial fossa.5
The point to remember is the proboscis is not a permanent structure.2 Instead, it’s a temporary assemblage of parts, sort of like your car jack. You take several metal pieces and join them together to form something that pumps. Once the job is complete, you dismantle the pump and stow the parts.
As the bee extends her glossa, she simultaneously wraps it in the four-part food canal. All the parts must be more-or-less snapped together so the food canal is watertight like a straw, and it all must happen at warp speed.
Remember, when you extend your tongue, you have only one part, one thing to go wrong. The bee employs many moving parts before she’s even tasted her find, and all that hardware must interact perfectly thousands of times per day. If she gets the timing off, I can imagine her biting her tongue — ouch! — much like a human does. Leave it to a bee to make life complicated.
Trophallaxis is the bee-to-bee transfer of liquids. After returning from a foraging trip, a nectar-laden honey bee enters the bustling hive and opens her mandibles to the house bees, displaying a drop of glistening nectar. A receiver bee then extends her proboscis toward the precious drop and vacuums it up.
The receiver adds more saliva to the nectar, a necessary stage in the manufacture of honey. The nectar may move from bee to bee more than once. Eventually, the partially-digested liquid will make it into a honey storage cell where it will be dehydrated by fanning until it’s concentrated enough to cap.
Water moves throughout the colony in the same fashion, except instead of offloading the water to just one or two bees, the water carrier spreads it among many. Like a bottled water dispenser, the water carrier allows the house bees to sip as needed.
In summer, bees also use water for temperature regulation. With their proboscises, the house bees spread water in a thin layer along the comb edges. Working like an air conditioner, the evaporating water cools the interior of the hive.
Highly social species such as honey bees also spread pheromones through trophallaxis, sharing social cues along with a treat. For example, queen substance is often distributed in this way, signaling the workers that their queen is alive and well. With the addition of pheromones, the mouthful of sweets functions like a fortune cookie, delivering sustenance as well as a message.
Forever blowing bubbles
The tongue and all its related parts can be useful in other ways. Just as honey bees spend a lot of time drying nectar to increase the sugar content, some solitary bees do the same. Even though they are not making honey, these bees often need a thicker, more syrupy nectar for brood rearing.
Solitary bees mix nectar with pollen when provisioning for their young. This mixture yields a type of bee bread nearly identical to that of honey bees. The nectar helps to keep the pollen moist, guards against spoilage, and likely makes the pollen more palatable. But if the nectar contains excess water, it is less protective of the pollen and can encourage mold growth.
While honey bees are busy passing nectar from bee to bee or fanning, the solitary bees are bubbling. The bee collects nectar until she has a full load, then she finds a comfortable place to sit such as a leaf, twig, or blade of grass. Once settled, she regurgitates a big bubble of nectar and exposes it to the air where it can dry. When the consistency is just right, she re-swallows it for transport back to her nest.6
If ever you see a female bee sitting idle in the sun, it pays to take a closer look. I saw one just last week, covered with pollen yet busily bubbling on a sunlit shaft of grass. She displayed an array of mouthparts with the shiny bubble right on top. The wind whipped her perch from side to side, yet she stayed put for over 15 minutes.
The extent of bubbling in the bee world is unknown, but it definitely seems more common in some species than others. Also, some regurgitate clear bubbles that are pure nectar, while others have cloudy bubbles that contain lots of pollen. If you’re looking for bubblers, try the green sweat bees (Augochlorini) and the masked bees (Hyleaus).
A sticky situation
Although we seldom think of a proboscis as a pollen-collecting tool, it is extremely hairy. The downy surface, especially after it’s been submerged in sugary nectar, is a pollen magnet.
We’ve all seen honey bees apparently grooming an extended proboscis with their forelegs, rubbing and stroking the entire length. Solitary bees do it too, often approaching a flower with both forelegs wrapped around a fully extended proboscis.
An incredible number of beekeeping books — maybe all of them? — say this is how honey bees remove errant pollen from the proboscis. However, according to Danforth et al., both long-tongued and short-tongued bees have brushes built into the labiomaxillary complex. These specialized brushes are designed for grooming the pollen from the forelegs. In other words, the bee moves pollen in the opposite direction, cleaning the legs instead of cleaning the proboscis.
Do we have that all wrong? Do our eyes deceive us? Probably. But that’s a story for another day.
Honey Bee Suite
Notes and References
- Mattingly RL. 2012. Honey-Maker: How the Honey Bee Worker Does What She Does. Portland, Oregon. Beargrass Press.
- Graham JM ed. 2015. The Hive and the Honey Bee. Hamilton, IL: Dadant & Sons.
- Burlew DA. 2019. The Marval of Mandibles. American Bee Journal. 159:6.
- Danforth BN, Minckley RL, and Neff JL. 2019. The Solitary Bees: Biology, Evolution, Conservation. Princeton, NJ. Princeton University Press.
- Winston ML. 1987. The Biology of the Honey Bee. Cambridge, MA: Harvard University Press.
- Houston T. 2018. A Guide to Native Bees of Australia. Clayton South, Victoria, Australia: CSIRO Publishing.