Sugar on the Tongue

This could be serious. Dry sugar may not be so great for bees after all, in contrast to liquid syrup.

A brief summary in the May 2022 issue of American Bee Journal 1 describes the findings of a study of the way bees handle dry sugar versus syrup, and the full report of this research can be found in an article noted below.2

It turns out that bees must dissolve a piece of solid sugar by licking it with very rapid back-and-forth tongue movements until a groove is made, while moistening it with saliva. 

Remember the hairs on the bee’s tongue? (See “Proboscis Anyone?” in the BEE BIOLOGY section of this blog.) Here’s where they are located (a) and (b), and how they appear (c), intact.

A honey bee’s tongue (glossa) is housed in the proboscis and is extended and moved rapidly up and down for lapping or licking fluids: (a) bee with tongue extended; (b) diagram showing proboscis closed, then spread open to reveal the glossa; (c) extended glossa (images: J. Chen[3])
 

Well, the research reveals that due to the friction involved in scraping away at the hard surface of sugar, those small tongue hairs―which are adapted to lapping liquid nectar―are worn down 4 times faster when the bee is feeding on dry sugar crystals than they are in their normal use for sipping fluids.1,2

Not only that! Consider the energy cost involved, as well.  A bee must work so hard to process a “mouthful” of dry sugar by scraping the tongue back and forth like a piece of rough sandpaper that “the net energy intake rate of feeding on dry sugar is 50% lower than when feeding on liquid solutions.”1,2

Photographic and corresponding drawn sketches showing a single cycle of a bee’s tongue extension from and retraction into the proboscis for lapping liquids. Timing of the cycle is shown in milliseconds (image: J. Chen[3])

That is, a bee must work twice as hard, expending twice the energy, to get the same number of calories from dry sugar as from liquid nectar or syrup.

Typically, we beekeepers only use dry sugar as an emergency food for our bees, particularly during late autumn and winter months if we have insufficient honey to offer.  

Regardless of the form of dry sugar provided—whether granulated, cubes, or even “candy”—it must be dissolved in water before bees can actually EAT it. 

That means it has to be dampened for to process it either by the bees’ saliva and licking, water condensation in the boxes, or droplets brought into the hive by water-foragers.

Otherwise, it is simply trash that will be carried outside to discard or be left in place, untouched.

What can we conclude from these research results?

In every case the beekeeper should decide carefully when and what to feed the bees.  The best- to worst-case choices are as follows:  the best is to feed honey (your own—not purchased from sources unknown) because it is the most healthful for the bees to consume. 

Crystallized honey is next, even though it also requires water to reliquefy.  Use sugar syrup when the honey runs out, particularly in spring/summer. And as a last resort, employ dry sugar in some form for late autumn or wintertime.

And finally, I wonder whether there might be some old Bee Proverbs handed down through the generations, such as  “Don’t wear out your tongue on useless stones, or “A spoonful of water helps the sugar go down” ….

Do you think so?

Notes:

1J. Ellis, 2022, The Classroom [Q&A: How do bees feed on table sugar?], American Bee Journal 162(5): 495.

2C. Liao et al. 2020, Feeding behavior of honey bees on dry sugar. Journal of Insect Physiology 124: 104059. https://doi.org/10.1016/j.jinsphys.2020.10459.

3J. Chen, J. Wu, and S. Yan. 2015, Switchable Wettability of the Honeybee’s Tongue Surface Regulated by Erectable Glossal Hairs, Journal of Insect Science 15: 10.1093.

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