I don’t know about you, but as a kid, I always associated that lovely word, proboscis, with elephants…well, maybe later on with tapirs, aardvarks, echidnas, and other such exotic creatures I read about, too.  Those are all vertebrate animals, and the term refers to their particular and peculiar type of nose.

In contrast, among invertebrates such as bees and butterflies, the term describes the tubular, usually extendible mouthparts for sucking nectar and water. 

In popular parlance concerning insects, the terms “proboscis” and “tongue” are often used interchangeably—a convention that we shall follow here.

THE HONEY BEE PROBOSCIS—In bees, the proboscis is a rather complicated item with various layers of structural sheathing that form a sturdy sucking tube, which, when in use, is reinforced and held in place by the clamp of the bee’s strong mandibles.

When not being used, the many-jointed appendage folds up neatly in a special groove on the underside of the head.

The inside of the proboscis consists of a smaller, narrower, extendible tube, the glossa, that could be called the “functional tongue.” It is covered with over 10,000 hairs that are especially dense on the bowl-like tip.

How does this specialized, double drinking-straw system work? 

When the bee is feeding on tiny amounts thick, syrupy nectar in a flower, the bristly tongue is thrust up and down at a rapid pace to quickly lap up the droplets that glom onto the densely packed, 100- μm-long hairs at each dip into the pot.

Every time the tongue is pulled back into the proboscis, a hollow, muscular bulb in the bee’s head works like a pump to suck the nectar off the tongue and pass it on toward the honey crop.

When the bee consumes a thinner nectar or water, the tongue remains quietly extended while the pump works to suck the pool of liquid to the same destination.

FEEDING AND TALKING THROUGH THE TUBE—Bees in the hive transfer food and water to nestmates by the process known as trophallaxis, using the proboscis to directly deliver the liquids from one bee to another. At the same time, bees pass on information in the form of pheromones.

For example, attendants that have licked and groomed the queen transfer a bit of the queen substance pheromone to nestmates when they pass on nectar and other liquids by this type of mouth-to-mouth contact.

Another kind of information is provided to workers by the quantity and quality of food in trophallactic circulation within the hive. This could influence the subsequent activity level of both foragers and hive workers to keep the colony appropriately supplied.

COMMUNING WITH FLOWERS—Features of each bee species’ proboscis developed over time as the bees coevolved with the flowering plants in their environment, ultimately arriving at a length and form that allows successful access to certain floral types. Some bees are specialists, with a narrow repertoire; others are generalists, with a broader range of flowers they can exploit.

The honey bee’s proboscis is nearly 7 mm long (¼ in.) fully extended—about half the average-sized worker’s body length. That puts Apis mellifera into the category of “long-tongued bees,” although it’s on the shorter end of that particular spectrum.

With this length of proboscis, honey bees are able to take nectar from a large variety of flower species from APPLE to ZINNIA and all the letters in between …. but they are limited when it comes to blossoms with longer floral tubes, such as fuchsia or campion.  

As a comparison, the various bumble bee species span the range of short, medium, and long-tongue categories with corresponding floral preferences, which helps them to partition the nectar sources in their habitat and thereby reduce competition.

Perhaps the most far-reaching bumble-tongue to be found is that of the small garden bumble bee, Bombus hortorum, to a maximum stretch of 20 mm (¾ in.).

However, considering all kinds of bees, not just bumbles, there is no contest when we look at the very farthest long-end of the scale: a small, colorful bee species discovered recently in the Colombian rainforest has a tongue that is twice as long as the bee: that is, the tiny bee is 16 mm in length, and its extended tongue is about 30 mm long.

This metallic-green bee, Euglossa natesi, coevolved as a pollinator for particular orchids with extraordinarily long floral tubes. A specialist, indeed!

GOOD GROOMING—Because of the fundamental importance of its function, the proboscis must be kept in perfect working order by frequent cleaning. Fortunately for the bees, the cleaning tool is built right in. They use their bristly-edged front legs to brush and polish this essential bit of equipment, a behavior that is readily observable if you watch the bees as they forage. 

So must the bees themselves and their queen be kept clean! The workers have that task “licked,” as well. Not only do they employ all their legs for brushing and grooming themselves, removing pollen from the body hairs and cleaning the sensory receptors on the body and eyes, etc., but the bees’ long tongue works perfectly well to complete the self-rubdown—also for grooming the queen, drones, and nestmates.

And finally, even the ol’ hive needs cleaning now and then. For this chore, there is a bee behavior known as “washboarding,” in which groups of workers gather on the hive exterior and landing platform and rock back and forth to give the floor a good group-scrub, scraping the surface with their mouthparts (read more on this topic on honeybeesuite.com/washboarding-bees-arockin-and-alickin/).

Conclusion: a matter of taste. No matter one’s taste in the style or length of a bee’s proboscis, the basic functions of every model of this wonderful tool are (a) to lap and to suck liquids and pass them on toward the honey crop; (b) to exchange such liquids with nestmates by trophallaxus; (c) to groom and clean oneself, the queen, and fellow workers; and (d) to communicate. 

But wait, there’s more! The mouthparts—especially the long, hairy glossa with its even hairier curved tip for lapping—also have taste receptors on their surfaces: tiny hairs to detect sweet tastes, primarily.

These are not the most sensitive, versatile, or numerous of the bee’s taste receptors, by far……but that is a matter for another Bee Biology article you can find on this blog: “The Honey Bee’s Good Taste.”

In the meantime…..proboscis, anyone?