by Jeanne McRight
When reading about the ecological benefits of native plants, you may have encountered descriptions of the plant species' special appeal to bees with long or short tongues. "Wait – bees have tongues?" you might be wondering...so here's a short dive into the curious and as scientists make surprising discoveries, amazingly complex world of bee tongues!
Curiouser and curiouser: adaptive evolution at its finest
First, the mouth structure of a bee is a wonderland of cleverly engineered parts, divided into main components of mandible, proboscis, and tongue, and then further into categories and subcategories each with its own name and function. A bee's entire body but especially its mouth parts are adapted to match the structure of the flowers that provide its sustenance. This adaptive process is not always in balance, and occasionally either the flower or the insect gains an advantage, upsetting the equilibrium, calling for ecological interventions if both species are to survive. In the case of the image above, a large-bodied bumblebee has such a long tongue that it is able to mop up the foxglove beardtongue's (P. digitalis) nectar without climbing into the blossom. Therefore, the flower does not get pollinated. Luckily the beardtongue also attracts smaller bees species such as mining bees who are its main pollinators. Once inside the blossom, mining bees have evolved the ability to vibrate their bodies (sonification aka buzz pollination) and the pollen showers down onto the bee's body hairs.
Tongues length matters
The earliest bee species to evolve had short tongues. Primitive flowers were shallow and their nectar was easily accessible to insects. As ancient flower species evolved, the corolla (petals that enclose the reproductive system) became deeper to protect their nectaries, so certain bee species adapted their tongue length as well.
Bees with long tongues are typically larger than their shorter-tongued counterparts. They are much more aggressive when defending their food source, proving that these adaptations help them survive better in the wild.
Some types of long-tongued bees include:
Apidae – The largest family of bees with more than 5,000 species, Apidaes include honey bees, such as the western honey bee (Anthophora affabilis) and bumblebees. Fun fact: bumblebees (Bombus) have the longest tongue of all bees!
Megachilidae – This family of bees includes leaf-cutting bees.
Anthophoridae – Pesky miner bees, carpenter bees, and parasitic bees are in the Anthophoridae family.
The short-tongued bees are a fascinating group to study because of their unique adaptation. Short-tongued bees must feed on flowers with shallow-to-medium-depth corollas requiring less effort and energy.
Therefore, those in the short-tongued bee family enjoy more diverse nectar sources.
Some short-tongued bee families include:
Colletidae – Includes cellophane bees (a.k.a. polyester bees, or plasterer bees) so-called because of the plastic-like substance used to line their brood cells.
Halictidae – This family includes sweat bees, which have some of the shortest tongues of all bee species.
Andrenidae – This family includes large, ground-burrowing solitary bees, called snowy miner bees (Andrena nivalis).
Slurp, sip, or lap?
Long tongued bees' tongues, seen under a microscope, look like a mop and function like a straw with a tubular handle and hair-like projections splayed at the end. They unfurl their mop-tongue into a flower and slurp up the nectar from the blossom’s depths, then fold them accordion-style under their body when not in use. Short-tongue bees have different tongue anatomies and may lap rather than suck up nectar.
Above, bumble bees like this common wool carder, have long tongues that fold under the abdomen when flying.
But what happens when the flowers disappear? A eureka moment...
Flowers and bees must continue to successfully co-evolve as they adapt to the pressures of climate change. Today’s bees face about 60 percent less food than their predecessors from the 1970s. For example, over the past 40 years, warmer, drier weather reduced flower populations in some regions of the Rocky Mountains in North America, forcing the prevailing species of long-tongued bees to work harder to find nectar. Over the same time period, something extraordinary happened: bee tongues in those regions became shorter, according to a 2015 study published in Science.
Bees are rapidly evolving to a warming world, in ways that threaten their intimate partnerships with long-tubed flowers. Fewer flowers meant not enough for long-tongued specialists to subsist on. So the long-tongued bees were forced to broaden their diets, drinking nectar from flowers of every length. Since they were now competing for resources that many other species could plunder, their long tongues no longer conferred any special advantages. So evolution, ever-thrifty and economical, selected for individuals with shorter tongues (Miller-Struttmann, et al. 2015).
According to Nicole Miller-Struttmann, the evolutionary ecologist who led the study, the change to the bees’ anatomy probably arose because longer-tongued bees tend to be picky eaters, dining mainly on nectar from deep flowers. When food became scarce, the bees adapted rather than move or starve.
Remarkable!
The results of the study were remarkable because they showed that the bees were capable of extremely rapid evolution.
Resources
The Interaction between Pollinator Size and the Bristle Staminode of Penstemon digitalis (Scrophulariaceae) Gregg Dieringer and Leticia Cabrera R. American Journal of Botany , Vol. 89, No. 6 (Jun., 2002), pp. 991-997
Stanley, Tim (2016). Digger Bees and the Beardtongue, Native Bee-ology https://nativebeeology.com/about/
Warmer temperatures and fewer flowers yield shorter bee tongues.
Ledford, H. Bee tongues tell a tale of climate change. Nature (2015). https://doi.org/10.1038/nature.2015.18430
Bee Tongues and Flowers Reveal Evolution in Overdrive
Changes in climate means there are fewer flowers. How will bees adapt?
GWEN PEARSON Wired, SCIENCE SEP 24, 2015
https://www.wired.com/2015/09/flowers-bees-no-longer-n-sync/
Miller-Struttmann, et al. 2015. Functional mismatch in a bumble bee pollination mutualism under climate change. http://www.sciencemag.org/lookup/doi/10.1126/science.aab0868